National Institute of Justice - NCJRS · National Institute of Standards and Technology (NIST) under the direction of A. George Lieberman, Program Manager for Communications Systems,

U.S. Department of JusticeOffice of Justice ProgramsNational Institute of Justice

National Institute of Justice

VIDEO SURVEILLANCE EQUIPMENTSELECTION AND APPLICATION GUIDE

NIJ Guide 201-99

Law Enforcement and Corrections Standards and Testing Program

ABOUT THE LAW ENFORCEMENT AND CORRECTIONS STANDARDS AND TESTING PROGRAM

The Law Enforcement and Corrections Standards and Testing Program is sponsored by the Officeof Science and Technology of the National Institute of Justice (NIJ), U.S. Department of Justice. The programresponds to the mandate of the Justice System Improvement Act of 1979, which created NIJ and directed itto encourage research and development to improve the criminal justice system and to disseminate the resultsto Federal, State, and local agencies.

The Law Enforcement and Corrections Standards and Testing Program is an applied research effortthat determines the technological needs of justice system agencies, sets minimum performance standards forspecific devices, tests commercially available equipment against those standards, and disseminates thestandards and the test results to criminal justice agencies nationally and internationally.

The program operates through:The Law Enforcement and Corrections Technology Advisory Council (LECTAC) consisting of

nationally recognized criminal justice practitioners from Federal, State, and local agencies, which assessestechnological needs and sets priorities for research programs and items to be evaluated and tested.

The Office of Law Enforcement Standards (OLES) at the National Institute of Standards andTechnology, which develops voluntary national performance standards for compliance testing to ensure thatindividual items of equipment are suitable for use by criminal justice agencies. The standards are based uponlaboratory testing and evaluation of representative samples of each item of equipment to determine the keyattributes, develop test methods, and establish minimum performance requirements for each essential attribute.In addition to the highly technical standards, OLES also produces technical reports and user guidelines thatexplain in nontechnical terms the capabilities of available equipment.

The National Law Enforcement and Corrections Technology Center (NLECTC), operated by agrantee, which supervises a national compliance testing program conducted by independent laboratories. Thestandards developed by OLES serve as performance benchmarks against which commercial equipment ismeasured. The facilities, personnel, and testing capabilities of the independent laboratories are evaluated byOLES prior to testing each item of equipment, and OLES helps the NLECTC staff review and analyze data.Test results are published in Equipment Performance Reports designed to help justice system procurementofficials make informed purchasing decisions.

Publications are available at no charge through the National Law Enforcement and CorrectionsTechnology Center. Some documents are also available online through the Internet/World Wide Web. Torequest a document or additional information, call 800-248-2742 or 301-519-5060, or write:

National Law Enforcement and Corrections Technology CenterP.O. Box 1160Rockville, MD 20849-1160E-Mail: [email protected] Wide Web address: http://www.nlectc.org

The National Institute of Justice is a component of the Officeof Justice Programs, which also includes the Bureau of JusticeAssistance, Bureau of Justice Statistics, Office of JuvenileJustice and Delinquency Prevention, and the Office for Victimsof Crime.

U.S. Department of Justice Office of Justice Programs National Institute of Justice

Video Surveillance Equipment Selection and Application Guide NIJ Guide 201-99

D.J. Atkinson, V.J. Pietrasiewicz, K.E. Junker Institute for Telecommunication Sciences Boulder, CO 80303 Prepared for: National Institute of Justice Office of Science and Technology U.S. Department of Justice Washington, DC 20531 October 1999


Jeremy TravisDirector

The technical effort to develop this Guide was conductedunder Interagency Agreement No. 94-IJ-R-004,

Project No. 97-029-CTT.

This Guide was prepared by the Office of Law Enforcement Standards (OLES) of the

National Institute of Standards and Technology (NIST)under the direction of A. George Lieberman,

Program Manager for Communications Systems,and Kathleen M. Higgins, Director of OLES.

The work resulting in this Guide was sponsored by the National Institute of Justice, David G. Boyd,

Director, Office of Science and Technology.

iii

FOREWORD

The Office of Law Enforcement Standards (OLES) of the National Institute of Standards andTechnology furnishes technical support to the National Institute of Justice (NIJ) program tostrengthen law enforcement and criminal justice in the United States. OLES’ function is to conductresearch that will assist law enforcement and criminal justice agencies in the selection andprocurement of quality equipment.

OLES is: (1) Subjecting existing equipment to laboratory testing and evaluation, and (2) conductingresearch leading to the development of several series of documents, including national voluntaryequipment standards, user guides, and technical reports.

This document covers research on law enforcement equipment conducted by OLES under thesponsorship of NIJ. Additional reports, as well as other documents, are being issued under theOLES program in the areas of protective clothing and equipment, communications systems,emergency equipment, investigative aids, security systems, vehicles, weapons, and analyticaltechniques and standard reference materials used by the forensic community.

Technical comments and suggestions concerning this document are invited from all interestedparties. They may be addressed to the Director, Office of Law Enforcement Standards, NationalInstitute of Standards and Technology, Gaithersburg, MD 20899-8102.

David G. Boyd, DirectorOffice of Science and Technology


Video Surveillance Equipment Selection and Application Guide

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v

A standard is not intended to informand guide the reader; that is the

function of a guideline

BACKGROUND

The Office of Law Enforcement Standards (OLES)was established by the National Institute of Justice(NIJ) to provide focus on two major objectives: (1)to find existing equipment which can be purchasedtoday, and (2) to develop new law-enforcementequipment that can be made available as soon aspossible. A part of OLES’ mission is to becomethoroughly familiar with existing equipment, toevaluate its performance by means of objectivelaboratory tests, to develop and improve these testmethods, to developperformance standards forselected equipment items,and to prepare guidelines forthe selection and use of thisequipment. All of theseactivities are directed towardproviding law enforcementagencies with assistance inmaking good equipment selections and acquisitionsin accordance with their own requirements.

As the OLES program has matured, there has been agradual shift in the objectives of the OLES projects.The initial emphasis on the development ofstandards has decreased, and the emphasis on thedevelopment of guidelines has increased. For thesignificance of this shift in emphasis to beappreciated, the precise definitions of the words“standard” and “guideline” as used in this contextmust be clearly understood.

A “standard” for a particular item of equipment isunderstood to be a formal document, in aconventional format, that details the performance

the equipment is required to give and describes testmethods by which its actual performance can bemeasured. These requirements are technical and arestated in terms directly related to the equipment’suse. The basic purposes of a standard are (1) to be areference in procurement documents created bypurchasing officers who wish to specify equipmentof the “standard” quality, and (2) to identifyobjectively equipment of acceptable performance.

Note that a standard isnot intended to informand guide the reader; thatis the function of aguideline. Guidelines arewritten in non-technicallanguage and areaddressed to the potentialuser of the equipment.

They include a general discussion of the equipment,its important performance attributes, the variousmodels currently on the market, objective test datawhere available, and any other information thatmight help the reader make a rational selectionamong the various options or available alternatives.

This video surveillance equipment guide is providedto inform the reader of the principles that can beused to select video surveillance equipment that willmeet the requirements of the application where itwill be used.

Kathleen HigginsNational Institute of Standards and Technology

August 1999


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CONTENTS

FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiBACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . vCONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . viiiList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . viiiCONVENTIONS USED IN THIS GUIDE . . . . . ix1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. Video Surveillance Requirements . . . . . . . . . . . 3

2.1 Typical Video Surveillance Assignments . 32.2 Other Survey Results . . . . . . . . . . . . . . . . . 42.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3. Description of Video Surveillance Componentsand Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 73.2 Video Cameras . . . . . . . . . . . . . . . . . . . . . . 7

3.2.1 Technology Summary . . . . . . . . . . . . 73.2.2 Video Camera Features . . . . . . . . . . . 93.2.3 Camera Lenses . . . . . . . . . . . . . . . . 113.2.4 Still Video Overview . . . . . . . . . . . 143.2.5 Low-Light Cameras . . . . . . . . . . . . 143.2.6 Infrared Cameras . . . . . . . . . . . . . . . 15

3.3 Camcorders and Recorder/Players . . . . . . 163.3.1 Video Tape Technology . . . . . . . . . 163.3.2 Camcorders and Video

Recorder/Players Features . . . . . . . . . 173.3.3 Camcorder Accessories . . . . . . . . . . 213.3.4 Format Applicability to Surveillance

Requirements . . . . . . . . . . . . . . . . . . . 223.4 Monitors/Televisions . . . . . . . . . . . . . . . . 23

3.4.1 Technology Summary . . . . . . . . . . . 233.4.2 Monitor/Television Features . . . . . . 27

3.5 Special Surveillance Systems . . . . . . . . . . 283.5.1 Specialized Camera Systems . . . . . 283.5.2 Patrol Car Surveillance Systems . . . 283.5.3 Retractable Surveillance Systems . . 293.5.4 Portable Systems . . . . . . . . . . . . . . . 29

4. Quality Parameters and the User – InterpretingManufacturers' Specifications . . . . . . . . . . . . 314.1 Technical Parameters' Relationship to Law

Enforcement and Corrections Needs . . . . 314.2 Parameter Definitions. . . . . . . . . . . . . . . 32

4.2.1 Resolution. . . . . . . . . . . . . . . . . . . . 324.2.2 Signal–to–Noise Ratio. . . . . . . . . . 334.2.3 Minimum Illumination. . . . . . . . . . 344.2.4 Shooting Below the Light Threshold364.2.5 Color Accuracy. . . . . . . . . . . . . . . . 364.2.6 Maximum Lens Aperture. . . . . . . . 384.2.7 Minimum Focusing Distance. . . . . 384.2.8 Zoom. . . . . . . . . . . . . . . . . . . . . . . . 384.2.9 Autofocus. . . . . . . . . . . . . . . . . . . . 394.2.10 Shutter Speed Control. . . . . . . . . . 40

5. The Ergonomic Aspects of Equipment . . . . . . 415.1 Time Needed to Learn Basic and Advanced

Operations . . . . . . . . . . . . . . . . . . . . . . . . 415.2 Controls – What Kinds Are Better?. . . . . 415.3 Camcorder Use With Gloves and Other

Heavy Clothing . . . . . . . . . . . . . . . . . . . . 425.4 Weight and Handling Versus Steadiness

When Operating . . . . . . . . . . . . . . . . . . . . 425.5 Equipment Compatibility. . . . . . . . . . . . . 435.6 Helpful and Useless Features. . . . . . . . . . 435.7 Viewfinders . . . . . . . . . . . . . . . . . . . . . . . 435.8 Battery Life and Replacement . . . . . . . . . 445.9 Tapes – Cost Versus Quality; Problems

Reading Tapes . . . . . . . . . . . . . . . . . . . . . 445.10 Maintenance for a Machine With Tape

Heads? . . . . . . . . . . . . . . . . . . . . . . . . . . . 455.11 Documentation/Instructions. . . . . . . . . . 45

6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Appendix A: Information Resources on the Web 57Appendix B: Effect of Low-Light Situations on

Cameras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59B.1 Working in Less-Than-Ideal Light . . . . . 59B.1.1 Enhancing the Images. . . . . . . . . . . . . . 62B.2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 68


viii

List of FiguresFigure 1. Example of a CCD camera . . . . . . . . . . . 8Figure 2. A CCD pickup device mounted in a

camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Figure 3. Controls for camera shown in Figure 1 10Figure 4. 50 mm, f-1:1.4 manual camera lens . . . 11Figure 5. Camera lens with aperture wide open (left)

and partially closed (right) . . . . . . . . . . . . . . . 12Figure 6. Typical microcamera system . . . . . . . . 13Figure 7. Wide angle (top) and telephoto pinhole

lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Figure 8. Example of a board camera . . . . . . . . . 14Figure 9. Left side of a typical digital video

camcorder . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Figure 10. Right side and rear of a typical digital

video camcorder . . . . . . . . . . . . . . . . . . . . . . . 19Figure 11. Example of a camcorder with both a

viewfinder and an LCD monitor . . . . . . . . . . 20Figure 12. Extracting useful data from videotape

shot in conditions below the light threshold . 37Figure B-1. Effect of diminishing light level on

image integrity (A, minimum distance) . . . . . 60Figure B-2. Effect of diminishing light level on

image integrity (B, minimum distance) . . . . . 61Figure B-3. Effect of diminishing light level on

image integrity (A, maximum optical zoom) . 63Figure B-4. Effect of diminishing light level on

image integrity (B, maximum optical zoom) . 64Figure B-5. Effect of diminishing light level on

image integrity (A, maximum digital zoom) . 65Figure B-6. Effect of diminishing light level on

image integrity (B, maximum digital zoom) . 66Figure B-7. Effect of diminishing light level on

ability of signal processing techniques toimprove image integrity (A, maximum opticalzoom) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

List of TablesTable 1. Video Surveillance Assignments . . . . . . . 3Table 2. Operating Conditions Affecting

Surveillance Performance . . . . . . . . . . . . . . . . 3Table 3. Subclassification of Select Usage

Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Table 4. Breakdown of Video Equipment Types . 8Table 5. Price Ranges for Various Video

Surveillance Equipment Formats . . . . . . . . . . 20Table 6. Surveillance Applications and

Recommended Equipment . . . . . . . . . . . . . . . 24Table 7. Equipment Recommendation for Various

Surveillance Resolution Requirements . . . . . 25Table 8. Test Parameters’ Relationship to Law

Enforcement and Corrections Needs . . . . . . . 31Table 9. Typical Light Levels Based on Outdoor

and Indoor Conditions . . . . . . . . . . . . . . . . . . 35Table 10. f-Numbers and Light Brightness . . . . . 38Table B-1. Cameras Used in the Low-Light

Experiment and Their Specifications . . . . . . . 59

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CONVENTIONS USED IN THIS GUIDE

To improve the readability of this document, several type-face conventions have been adopted. These are asfollows:

Bold type indicates equipment and technologies that are discussed indetail in the “Description of Video Surveillance Componentsand Systems” section of this guide.

Italic type indicates terms that are defined in the glossary.

Underlined type identifies brand names or specific equipment used in thedevelopment of this guide.


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COMMONLY USED SYMBOLS AND ABBREVIATIONS

A ampere H henry nm nanometerac alternating current h hour No. numberAM amplitude modulation hf high frequency o.d. outside diametercd candela Hz hertz (c/s) ohmcm centimeter i.d. inside diameter p. pageCP chemically pure in inch Pa pascalc/s cycle per second ir infrared pe probable errord day J joule pp. pagesdB decibel L lambert ppm part per milliondc direct current L liter qt quart C degree Celsius lb pound rad radian F degree Fahrenheit lbf pound-force rf radio frequencydia diameter lbf in pound-force inch rh relative humidityemf electromotive force lm lumen s secondeq equation ln logarithm (natural) SD standard deviationF farad log logarithm (common) sec. sectionfc footcandle M molar SWR standing wave ratiofig. figure m meter uhf ultrahigh frequencyFM frequency modulation min minute uv ultravioletft foot mm millimeter V voltft/s foot per second mph mile per hour vhf very high frequencyg acceleration m/s meter per second W wattg gram N newton wavelengthgr grain N m newton meter wt weight

area = unit2 (e.g., ft2, in2, etc.); volume = unit3 (e.g., ft2, m3, etc.)

PREFIXES

d deci (10-1) da deka (10)c centi (10-2) h hecto (102)m milli (10-3) k kilo (103)µ micro (10-6) M mega (106)n nano (10-9) G giga (109)p pico (10-12) T tera (1012)

COMMON CONVERSIONS (See ASTM E380)

0.30480 m = 1ft 4.448222 N = lbf2.54 cm = 1 in 1.355818 J = 1 ft lbf0.4535924 kg = 1 lb 0.1129848 N m = lbf in0.06479891g = 1gr 14.59390 N/m = 1 lbf/ft0.9463529 L = 1 qt 6894.757 Pa = 1 lbf/in2

3600000 J = 1 kW hr 1.609344 km/h = mph

Temperature: T C = (T F 32)×5/9

Temperature: T F = (T C×9/5)+32


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1

1. Introduction

In this era of rapid technical advancement, themarketplace is flooded with a tremendous variety ofvideo equipment. This can be both good and bad. Itis good from the standpoint that a potential purchaserof video equipment can almost certainly find acommercially available video unit or package that willmeet perceived needs and desires. However, whenthose needs are not clear, or are changing, and thecharacteristics of the equipment are not understood,the number of equipment choices can lead thepurchaser to a feeling of confusion or helplessness.Video equipment salespeople can confound the issuefurther by advocating the purchase of products whichhave attractive (but unnecessary) features andcapabilities, or by simply recommending the morewell-known manufacturers’ products, which tend to bemore expensive.

Personnel in the law enforcement and correctionsagencies wishing to utilize video surveillance systems(for collecting evidence and promoting officer safety,for example) are challenged when required to confrontthese equipment choices and sales pressures whilestaying within an established budget. The purpose ofthis guide is to assist those law enforcement andprocurement officials who are not technically trainedin video equipment in the selection and application ofvideo surveillance equipment that will satisfy theirneeds. This guide primarily addresses general-usevideo equipment, including separate video cameras,self-contained camcorders, video recorders/players,and video display systems (monitors). However,special-purpose video equipment is also described,such as the Patrol Car Surveillance System.1

The guide begins with a discussion of typical videosurveillance assignments, that is, a definition of userrequirements for the law enforcement and correctionscommunities. This requirements definition serves asa jumping-off point and reference base for allsubsequent deliberations in later sections of the guide.An overview of the available video technology ispresented next, along with a summary of tape formats.A delineation of the technical parameters that mostinfluence operational performance for the varioustypes of gear follows. Guidance is provided regardingthe application of specific types of video equipment tomeet functional requirements. Another importantelement of the guide is information on the latestadvancements in video technology and the effectsthose advancements will have on surveillance work.With cost information, the functional requirementsdata will help sort out the lowest cost equipment thatcan effectively satisfy at least the minimallyacceptable surveillance requirements established bythe law enforcement and corrections community.

The appendices offer detailed experimental methodsand results that are summarized in the main text. Thiswill assist advanced users in determining what typesof tests might be appropriate when evaluating newequipment for use in their application environment.

1 Certain commercial companies, equipment, instruments,materials, and organizations are mentioned in this report toadequately explain the experiments and their results. In no casedoes such identification imply recommendation or endorsementby the National Institute of Justice, or any other U.S.Government department or agency, nor does it imply that thoseidentified are necessarily the best available for the purpose.


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2. Video Surveillance Requirements

2.1 Typical Video Surveillance Assignments

In order to develop a guide that would be useful to thelaw enforcement and corrections community, it wasfirst necessary to determine the community’s videosurveillance needs. This was accomplished throughthe development of a survey to which state and locallaw enforcement agencies responded. The surveyfocused on uncovering the kinds of video surveillanceassignments required of a typical police department.Those assignments (and the particular users’ needs toaccomplish the assignments) would lead naturally tothe specifications for equipment. Table 1 presents aset of representative surveillance assignments basedon results from the survey.

Table 1. Video Surveillance Assignments

Building or area access Record forensic data

Building or areasecurity

Operation/protectivedetail coordination

Crowd monitoring Video mug shots

Monitor officer onroutine stops

Record physicalevidence

Search and rescue Indoor surveillance

Monitor officer/suspectin dangerous situation

Record interrogations/polygraphexaminations

Monitor confinementareas

Record bomb squadwork

Outdoor surveillance Vehicular surveillance

Record crime scene Airborne surveillance

Besides the basic functional assignments, a completedescription of video surveillance applications mustaddress performance under certain operatingconditions. One of the most obvious of theseconditions is the environment to which the equipmentwill be subjected. However, there are other operating

conditions that can affect the usefulness of theequipment and the success of the surveillanceassignment. They can be placed into two broadcategories – usage and power requirements. Table 2contains a list of environmental, usage and powerconditions that can potentially affect the performanceof a surveillance system.

Table 2. Operating Conditions AffectingSurveillance Performance

Environmental

TemperatureMoistureCorrosive elementsShock/Vibration

Heat and/or coldPrecipitation, humiditySalt air, dust, sandTolerance

Usage

LightDistanceClarityRecord timePhysicalShutter speed

Minimum requirementsUseful rangeFaces or figures/activitiesMaximum time unattendedSize/weightSensitivity to motion

Power

Source

Battery life

Recharge cycles

AC only/car battery/ battery packOverall life/maximum number of chargesDischarge/recharge time

It is necessary to define in finer detail the scope ofthree of the most important usage requirements: light,clarity, and distance. The range of values for eachusage condition will help determine the feasibility ofusing certain types of video equipment and theminimum equipment specifications required of them.For example, lighting levels must be classified toreflect various indoor and outdoor settings.


4

Clarity, as a usage condition, is meant to relate howexplicit the surveyed image has to be to satisfy theintended use of the user. From a law enforcement andcorrections perspective, clarity can be subdivided intotwo quality levels – being able to identify faces, andbeing able to identify figures and activities. Distanceclassifications are related to the clarity of images andto typical scenarios of police operations (i.e., wherethe police are and where the subject is). Table 3summarizes the subclassifications of light, clarity, anddistance conditions.

Table 3. Subclassification of Select UsageConditions

Parameter Subclassifications

Light Daylight, indoor, nightwith dim light, nonoticeable light

Clarity Facial detail, figuresand activities

Distance Less than 50 yards, 50to 200 yards, greaterthan 200 yards

2.2 Other Survey Results

The survey revealed that there are several areas ofinterest to the law enforcement and correctionsagencies. The area that elicited the most interest wasstill video, a newer technology that shows muchpromise for the surveillance community. Agenciesbelieve this will be particularly useful in recordinginformation at the scene of a crime, but it will also beuseful for video mug shots and forensic datacollection. Also of great interest was low-light,amplified-light and infrared video equipment for usein night surveillance. This would be used primarilyto provide a means to track the movements ofsuspects, and to better perform building and areasurveillance. The third significant area of interest wasidentification of suspects at distances greater than200 yards. Where equipment is concerned, slightly

more agencies currently procure more general-purpose equipment than specialized equipment. Themost common piece of equipment in use is aconsumer quality (VHS, S-VHS, 8 mm, or Beta)videocassette recorder. The other two most commonpieces of equipment in use are low to mediumresolution color cameras and low to mediumresolution camcorders. The frequency of use of thesetypes of equipment is logical in that they are theeasiest to obtain and use. However, they are not theonly type of equipment in use. The only piece ofequipment that the surveys did not indicate was in usewas a camera concealed on a person. In light of thissurvey result, body cameras are not included in thisguide.

The physical treatment of video equipment can varygreatly. Many pieces of equipment are subjected tovibration, moisture, and both heat and cold, whileothers are only used in environmentally controlledareas. The field storage conditions of the equipmentalso vary greatly. They range from custom mounts invehicles to car trunks and seats. The temperatures inthese surroundings can vary more than the usage(outside) conditions, especially if the car isunoccupied for more than 30 min at a time. Thepermanent storage space for the equipment, however,is fairly consistent: usually an office environment orair-conditioned room.

Also of interest is the agencies’ video equipmentoperators. Survey responses indicate that most of theagencies have video specialists who are the only onesto operate video equipment. There is also, however,a significant number of responses from agencieswhere everyone is required to operate at least somevideo equipment.

One area of possible concern is the amount of trainingavailable for the video equipment operators. Only oneagency reported that it had more than 2 percent of itstraining budget available for training on themechanics and techniques of video equipment usage.Several reported that no budget was available for thistype of training.

Video Surveillance Requirements

5

2.3 Summary

Video surveillance requirements for law enforcementand corrections span a number of different appli-cations but may be cataloged into a fundamental set ofsix areas. These requirements areas are:

1. Identifying subjects (including persons) atvaried distances and at varied light levels. Differentquality levels of identification are required fordifferent applications (e.g., positive facial identifi-cation of persons under surveillance versus identifi-cation of persons breaking into a building to promptsecurity forces to respond).

2. Recording/documenting data and/or evidenceduring or after a crime. Exact color may be veryimportant to immediately apprehend a suspect basedon what he/she was wearing, or it may be necessary torecord precisely the hue of mud at a crime scene.

3. Handling scenes/locations with multiple act-ivities and/or multiple subjects. The responsivenessof cameras or camcorders may make the differencebetween capturing on film only one illegal act orseveral.

4. Covering indoor and outdoor activities indifferent geographic areas. No two police depart-ments deal with exactly the same environment.

5. Establishing multi-purpose flexibility so as toallow selected equipment to operate with otherexisting or new equipment. Equipment suites requirephysical and functional compatibility.

6. Promoting operational effectiveness. The bestequipment in the world will not produce results if itcannot be used by law enforcement and correctionspersonnel effectively when it is required. Limitationson training budgets make it mandatory that equipmentoperation also be straightforward.


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3. Description of Video Surveillance Componentsand Systems

3.1 Overview

When selecting equipment for video surveillanceapplications, there are a number of choices to make.This section reviews the four basic types of videosurveillance equipment – cameras, camcorders(camera-recorders), recorders/players, and videodisplays (monitors/televisions) – that can be used (insome combination) to form a complete video system.Cameras are presented first. In the technologydescription, the difference between tube and solid-state (i.e., charge coupled device [CCD]) cameraunits is explained, as well as differences betweenanalog and digital cameras and camcorders. After asummary of video camera features and an outline oflenses, two special camera types are described. Still-video cameras and low-light cameras are addressed inthe context of continuing and emerging lawenforcement applications.

Since magnetic tape is the primary storage mediumused in video equipment, a description of videotapetechnology and quality has been included at thebeginning of the discussion related to tape machines(i.e., camcorders and recorders/players). Wheretaping is concerned, there are six video tape formats(and their derivatives) that are applicable to videosurveillance: D1, D5, DV, Betacam™ (analog anddigital), VHS, and 8 mm. In many cases, the tapeformat and its inherent capabilities will stronglyinfluence equipment selection.

Any discussion of video surveillance equipmentbecomes confusing immediately unless the equipmenttypes (camcorders, etc.) are categorized into smaller,similar groups based on quality levels. There are twoprimary performance parameters that can be used todifferentiate quality levels for each video equipmenttype – resolution and color. Resolution, expressed

simply, is how clearly one can distinguish the detailedparts of an image. Color relates to the ability ofequipment to record, display, or playback color orblack and white images. These performanceparameters, and other equipment characteristics thatdirectly influence the quality levels of videoequipment, will be explained fully in later sections ofthis guide.

Table 4 presents the breakdown of equipment typesbased on their quality levels. Equipment types withlow- and medium-resolution capability have beenlumped together (within a color or black and whitecategory) because they employ essentially the sametechnology. The equipment with the greater(medium) resolution has taken advantage of latertechnological refinements to achieve a higher qualitylevel. High-resolution video gear (also broken downby a color or black and white capability) wasespecially planned and designed to accommodatehigh-quality applications, such as commercialtelevision production and broadcast. It is unlikely thatlow- and medium-resolution equipment will evermigrate to the levels of the high level gear throughsubsequent design refinements. As with mostelectronic equipment, it will be shown later thatimprovements in video equipment capability andquality result in differences in price; mostsignificantly as the equipment quality jumps from amedium-resolution level to one of high-resolution.

3.2 Video Cameras

3.2.1 Technology Summary

Tube cameras have been around since the beginningof television and the electronic video industry. Therehave been several names associated with tubecameras, including Vidicon™, Saticon™, and


8

Figure 2. A CCD pickup device mounted in a camera

Figure 1. Example of a CCD camera

Plumbicon™. However, these names always have thesame implication: electron tube video pickup. Arelative newcomer in the video world is the CCD(Charge Coupled Device). Figure 1 contains anexample of a CCD camera. A CCD camera uses lightsensitive semi-conductor technology as a video pickupdevice. As mentioned later, CCDs have gained asignificant share of the market and will eventuallytotally displace electron tubes as pickups. Seefigure 2 for an example of how a CCD pick-up isinstalled in a camera.

Table 4. Breakdown of Video Equipment Types

EquipmentType

Breakdown of category

Cameras 1. Low & medium resolution black & white2. Low & medium resolution color3. High resolution black & white4. High resolution color

Camcorders 1. Low & medium resolution2. High resolution

TapeRecorder/Players

1. VHS, S-VHS, 8 mm and Beta format2. U-Matic, Betacam™, 1" and digital formats

Displays 1. Low & medium resolution black & white2. Low & medium resolution color3. High resolution black & white4. High resolution color

SpecializedEquipment

1. Low-light, intensified-light, infrared2. Still video

There are several differences that can be directlyattributed to the fact that one technology is solid-stateand the other is tube-based. First is sensitivity tolight. It is true for both CCD and tube cameras thatmore light helps the camera generate better pictures.However, for low-level lighting, standard CCDdevices tend to produce a higher quality picture at a

given light level than their tube counterparts. Specialformulations of CCDs are available to make themeven more sensitive in very-low-light level situations.For very-high-level lighting situations, CCDs have theadvantage, also. When photographing bright lights,tube cameras tend to leave trails when displaying theimage, as the camera pans or the light source moves.This image persistence can cause damage to the tubeif the light source is sufficiently bright orphotographed for sufficient duration. CCD pickups,on the other hand, are virtually indestructible when itcomes to photographing light sources. CCDs never

have problems with image persistence and can only be

Description of Video Surveillance Components and Systems

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damaged by an intense heat source (e.g., created byfocused light from direct photography the sun).

Another difference between solid-state and electrontube pickups is the solid-state device has the ability tosimulate a shutter with an adjustable speed, while theelectron tube device cannot. This is because of themethod in which each device obtains the image data.A pick-up tube must continuously scan through ascene to provide a consistent image. For example, ifthe tube camera was being used to capture a colorimage for use by the television broadcast industry inthe United States, it would follow the NationalTelevision System Committee (NTSC) standard andscan through the 525 lines of the image 30 times persecond. A point of the image would be read, and thenthe scanning beam would move to the next point.This requires that the aperture between the scene andthe pickup device always be open. A CCD, on theother hand, obtains information about the whole sceneat the same time. Once the information from thescene has been registered onto the CCD, theinformation is translated to a scanning video signal bythe electronics of the camera. Because a CCDregisters all scene information simultaneously, ashutter can be placed between the scene and the pick-up. A high-speed shutter provides the potential forcrisp, still-frame images during action scenes (like re-plays of sporting events). This is the same methodthat is used for stop action in conventionalphotography. Like conventional photography,however, use of a high-speed shutter demands morescene lighting to obtain a good quality image becausethe imaging pickup device (film in the conventionalcamera and the CCD in the video camera) is exposedto the scene for a shorter period of time.

For low (240 lines, comparable to the VHS videotapeformat) or medium (400 lines, comparable to SuperVHS) resolution cameras, CCDs are much lessexpensive to produce than low-resolution tubes.Because of this, almost all cameras in this resolutionrange use CCDs as their pickup device.Until very recently, tubes were the only devices thatcould provide the quality needed for high-resolution

cameras (more than 500 lines). This, however, beganchanging as high-resolution CCD cameras enteredproduction in 1998. As reliability and production ofhigh-resolution CCDs increase, CCDs will take overthis segment of the market as they did for low- andmedium-resolution cameras. During the transitionphase, however, one must compare the advantagesand pricing of both CCD and tube cameras for high-resolution applications.

Another important innovation in video technology isthe advent of the digital camera. All of the traditionalcameras mentioned above provide output as an analogelectrical signal that can be stored on tape or viewedon a monitor. Recently, digital cameras have beenintroduced that output the video as a stream of bits(binary ones and zeroes) that can be understood bydigital displays or digital recorders. One advantage ofdigital video is the ability to make perfect copiesbecause the bit pattern used to create the displayedimage can be replicated exactly. Another advantage,specifically related to transmission, is digital videosignals are less prone to degradation over distance orin the presence of a weak or noisy signal. However,once the signal crosses a certain signal-to-noisethreshold, the loss is usually total, not the gradualdegradation experienced in traditional analog systems.

3.2.2 Video Camera Features

The basic specifications of video equipment give theuser a good, general idea of how a unit shouldperform. (These specified parameters are thoroughlyexplained in the next section of the guide, “QualityParameters and the User – Interpreting Manufacturers'Specifications”). Along with the characteristics of avideo camera that have a direct impact on its level ofperformance, however, other features are sometimesoffered that can either give the user added flexibilityand capability, or make the operation of the cameraeasier under different conditions. In some cases, theycan also enhance the fundamental ability of thecamera to perform better.


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Figure 3. Controls for camera shown in Figure 1

Below is a list of features that are offered in videocameras. Obviously, they will not all be offered in allmakes and models of cameras because cameras aremanufactured and sold to satisfy certain applicationsof the perceived market. The more features, thehigher the cost! If the “importance” of these featuresis not currently understood, their merits will becomeobvious later in the guide. Even without knowing thespecific details of individual video surveillanceassignments for all readers of this guide, it seemslikely that most will want to consider a number ofthese features. As a minimum, auto/manual whitebalance, auto-iris control, lens compatibility, multiplemounting holes, and environmental robustness aredesirable features. As a starting point towardunderstanding the available features, figure 3 showsthe controls for the CCD camera shown in figure 1.

White balance and/or black balance: Automatic,manual or remote-control – switch selectable.External white or black balance sensor possible.

RGB adjustments: Independent gain controls on red,green, blue, outputs. Remote control of red, green,blue, and master gain (i.e., overall video signal level).

Auto-iris control: For auto-iris lenses, an automaticgain control (AGC) or variable gain (e.g., 6 dB) –selectable on/off.

Synchronization options: Internal (crystal) or externalsource.

Power options: Ac or dc power options, typically12 V dc, 24 V dc or 115 V ac.

Lens Mount: Adjustable C-mount (adapter).

Lens compatibility: Accepts all (or most) types ofmanual and auto-iris TV lenses.

Electronic shutter: Enables the camera to produceclear images in still or slow-motion playback evenwhen the objects are moving at very high speeds.

Dynamic contrast control: Allows accommodation ofscenes with a much wider range of light levels thannormal (e.g., allows detail in both sun-lit and shadowyareas of the same scene).

Filters: Built-in optical filters can improve videoresults under various lighting conditions (e.g., bright,subdued, inside, outside).

Viewfinder compatibility: A jack is provided toaccommodate a viewfinder, if desired.

Microphone holder: An adjustable ring or some othertype of connection apparatus is provided on thecamera to mount a microphone.

Multiple mounting holes: Two or more tapped holesfor mounting the camera (e.g., on a tripod or wall-mounted bracket). More holes allow different size(and weight) lenses to be accommodated whilekeeping the assembly balanced.

Environmentally robust: Can operate in a widetemperature range (e.g., 14 °F to 122 °F) and can bestored in a wider range (e.g., -22 °F to 158 °F). Canoperate at altitude (e.g., 10,000 ft) and in heavyrelative humidity (e.g., 95 percent). Can tolerateshock and vibration.


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Figure 4. 50 mm, f-1:1.4 manual camera lens

Another thing to be aware of is a camera does notusually come as an all-inclusive video package.Components must be purchased along with it topermit it to function. A few of the most commonitems required for the camera system, but not suppliedwith it are listed below:

1. Ac power pack or ac/dc power supply2. Lens3. Coaxial cables (e.g., RG-59/U) for connections torecorder or monitor from “video out” jack, fromcamera to external sensor or synchronization, forremote control, etc.4. Television monitor for focusing and otheradjustments (such as white balance)

3.2.3 Camera Lenses

One important component of the video camera systemis the lens. A lens for a video camera plays the samerole as a lens for a 35 mm single lens reflex (film)camera. It allows the user to capture an image in thecamera. Why all the different lenses? The differencein lenses is dictated by the difference in shootingenvironments and the kind of pictures that are needed.In a nutshell, the size of the subject, the distance tothe subject, and how much light is on the subjectdetermines the best lens. Figure 4 shows a fairlysimple, manual focus, manual aperture lens.

The primary specifications of all camera lenses aretheir focal lengths and their f-stop ratings. Focallength is the distance from the center of the lens to thepoint at which parallel rays from a distant subjectcome to a common focal point. The f-stop number isthe ratio of the focal length to the diameter of the lens.These terms are explained below.

The size of an image that a lens forms inside thecamera is determined by three things – the physicalsize of the subject, the distance from the lens (camera)to the subject, and the focal length of the lens. Lenseswith a short focal length (for example, 8 mm to20 mm) are normally used for wide-angle pictures andare called "wide-angle" lens. Lenses with long focal

lengths (80 mm to 300+ mm) are used to capturedistant subjects and make them look close. Theselenses are generally called “telephoto” lenses. Amiddle-of-the-line kind of focal length is 50 mm.Many new single reflex cameras come with a 50 mmlens because camera manufacturers feel it will givegood overall performance for general recreational useson the average. It cannot do wide angle or telephotoshots. Because lenses have different focal lengths,they also have different coverage ratios. That meansthat their fields of view vary. The camera/lens field ofview is how much of the subject and the immediatesurroundings will be filmed.

A wide-angle lens has a tremendous field of view. Ifobserving a person on the street with a 16 mm camerasystem mounted on the side of a building, several feetof the street, both sidewalks, and other buildings maybe in view. For a telephoto lens, just the oppositehappens. A 300 mm lens camera may capture thehead of a subject at 100 ft and nothing else. The lightand viewing angles from the lens to the subject arevery narrow. In both simple cases given here, theability of the lens to satisfactorily capture the videoimage is dependent upon the light present. That factleads to a discussion of the f-stop parameter.


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Figure 5. Camera lens with aperture wide open(left) and partially closed (right)

The light-gathering ability of a camera is determinedby the diameter of the lens. The larger the diameter ofthe lens, the greater the amount of light falling on thesubject. Lenses are rated at maximum diameter (i.e.,the largest iris opening). (The iris is either fixed atone size or is an adjustable diaphragm that varies theopening for light to enter the lens. The opening itselfis called the aperture.) A lens’ so-called f-rating isdefined as the focal length of the lens divided by itsdiameter (with the iris fully open). The smaller the f-rating, the more light the lens can take in. This meansthat a low f-number is needed when a scene has lowlight. High f-numbers operate well in bright sunlight.

If a lens with a fixed iris and a 50 mm focal lengthhad a diameter of 35.7 mm, its f-rating would be 1.4.The iris ring would probably have the rating f-1.4written on it. This lens would work well in a fixedlocation with fairly low light. If a lens with anadjustable iris had a focal length of 25 mm and adiameter of 13 mm with the iris completely open, itsf-rating would be 1.9. On the movable iris, calibratedmarks called f-stops would indicate to the user thatbesides the f/1.9 setting, other settings for brighterlight conditions were also available by turning the irisring. These f-stops might be: 2.8, 4, 5.6, 8, 11, 16,and 22. The f-stop numbers increase in steps so thateach higher stop allows one half the light input of theprevious stop. For bright sunlight, f-22 is selected.Figure 5 shows a camera lens with the aperture wideopen and also with the aperture partially closed.Auto-iris lenses control the light level automatically.

One important consideration in video cameraoperation that is affected by the lens opening, f-stop,is the depth of field. The depth of field is the distancebetween the object in focus closest to the camera andthat object farthest from the camera that remains infocus. An example of this is clearly seen in atelevision scene when the camera is focused on aperformer close to the camera and the backgroundgoes out of focus. When the f-stop is lowest (iris fullyopened), the depth of field is poorest. To captureeverything in focus within the field of view, thecamera system must have the f-stop set as high as

possible (ideally at f/16 or f/22). Once lighting isreduced, however, only lower f-stops will capture anyimage successfully. This correspondingly reduces thedepth of field.

Zoom Lenses

Zoom lenses have continuously variable focal lengths.This reduces the need to change lenses for differentapplications. Wide-angle and telephoto tasks can besatisfied by the same camera with the same lens. Agood zoom lens may vary from less than a 10 mmfocal length to more than 140 mm with an f-stop ofonly 1.8. Zoom lenses are specified by the ratio of theminimum and maximum focal lengths. For a lens thatcan produce focal lengths from 9.5 mm to 143 mm, itszoom range is 143 divided by 9.5, or 15. Productliterature would express this ratio as 15:1 or 15X.

An important consideration in zoom lenses is whetheror not the aperture changes as the focal lengthchanges. Variable aperture zoom lenses are lenseswhose maximum aperture changes, generallyincreasing, as the lens is zoomed from smallest focallength to longest focal length. Fixed aperture zoomsmaintain the same maximum aperture throughout thezoom range of the lens. Fixed aperture zoomsgenerally provide better quality than variable aperturezooms. However, variable aperture zooms aregenerally less expensive and smaller than their fixedaperture counterparts.


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Figure 6. Typical microcamera system

Figure 7. Wide angle (top) and telephoto pinholelenses

Lenses for Special Camera Systems

A number of ultra-small color and black and whitecamera systems, sometimes called microcameras, areavailable that have a separate control unit and aseparate camera head connected by a cable. (fig. 6.)The control unit (box) contains the circuitry andadjustment controls (e.g., white balance, noisereduction, high-speed shutters, internal/external sync)normally found in and on the camera body, while thecamera head includes the lens and sensor subsystems.The reason for having such a camera system is that itcan essentially be placed virtually anywhere. It is anideal and versatile tool for several industrialapplications such as the observation of processes,material handling, quality control, and laboratoryexperiments. In addition, it can be used veryeffectively for video surveillance.

The camera control unit is small and light. Typicaldimensions might be: less than 4 1/2 in wide, lessthan 6 1/2 in deep, and about 1 1/2 in high. It mayweigh less than 2 lb. The cables, which connect thehead to the control unit, can be several lengths – froma few feet to almost 100 ft. The camera head comeswith a standard C-mount to accommodate a virtual“catalog” of different lenses. Those lenses can be asdiverse as the lenses used in a normal one-piececamera system. They range from “super wide angle”to telephoto, and many are available in a pinhole lensdesign.

Pinhole lenses vary in size but have one attribute incommon: their front element is very small and theiroverall construction mirrors this. Even with lenses of

focal lengths as low as 4.5 mm and as high as200 mm, the diameter of the lens barrel (the cylinderthat houses the lens) is normally only about an inch indiameter. The lens opening at the end of the lensbarrel may be just a few millimeters in diameter. (Theconversion of millimeters to inches is: 25.4 mmequals 1 in.) This means that a pinhole lens couldlook through a hole (e.g., in a picture, wall or door),that was about the size a pin would make. As anactual example, among the lenses that Knox SecurityEngineering Corporation sells are two very differentproducts – the model SXZ4.5 auto-iris 4.5 mm lensand the model YX200 200 mm manual lens (fig. 7.).The wide-angle SXZ4.5 has a lens opening of1.6 mm, about 1/16 in. The "huge" 200 mm telephotolens needs an opening of 10 mm, a little more than 3/8of an inch. Figure 7 shows the profiles for theselenses and their barrels, and gives their specifications.

Another tiny camera system is called a “boardcamera.” Board cameras are CCD devices with asmall lens and all other required electronics mountedon an electronic circuit board. The board is typically1.5 in square and requires that video output cables anda power input source be wired (and typically soldered)to the board. These cameras can be particularly usefulin cases where a traditional camera simply will not fit.Figure 8 illustrates a board camera that is approx-imately 1.5 in square.


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Figure 8. Example of a board camera

3.2.4 Still Video Overview

Still video, or digital still camera, technology was firstdemonstrated to the public in 1981. The devicedemonstrated at that time was revolutionary. It useda CCD to capture a video image, which was thenstored on a matchbook-sized floppy disk. The diskwas capable of holding 25 frames of video or 50 fieldsof video (a field is the equivalent of every other scanline of a frame). The images stored on the disk couldbe viewed on any standard television or printed on aspecial printer. The combined cost of the disk and thepaper and printer dye was significantly less than thecost of a standard print. The problem with the devicedisplayed in 1981 was a lack of resolution. The stillvideo camera at that time had a horizontal resolutionof about 200 lines, significantly less than a VHSrecorder would have. Because of the poor resolutionavailable, actual production of still video equipmentwas delayed until 1986. The equipment introduced in1986 showed vastly improved resolution. The

manufacturers had doubled the initial resolution tosomething that is comparable with Super VHS, i.e.,400 lines. Development has continued, andmainstream still video cameras can now be purchasedthat have a resolution of more than 700 lines. Thereare some very specialized digital cameras that have aresolution of more than 2,000 lines. This isapproaching the resolution of 35 mm film, which hasa resolution of about 4,000 lines to 6,000 lines,depending on the type of film.

One of the most touted features of still video is theability to take and view pictures instantly. With stillvideo, there is no need for messy, time consumingand costly development of slides or prints. Also, theimages recorded on the disk can be sent in digitalform anywhere instantly with no loss of quality.Finally, unlike film, the floppy disks that are used tostore image data can be used again once unusable orunneeded pictures are deleted.

3.2.5 Low-Light Cameras

Low-light CCD cameras can be categorized into twotypes: low-light and low-light intensified. The simplelow-light variety uses the same technology as “normallight” CCD cameras and camcorders; the difference isthat their imaging chips are optimized for low-lightconditions and/or have additional refinements to bemore noise-free over an expanded range of incidentlight.

In low-light video surveillance situations, standardCCD chips have one particular advantage over theirpredecessors, video pickup tubes: their resistance toimage burn-in caused by incident light that is toointense. If a video tube were to focus on a scene thatcontained an overly intense light source, an image ofthat light source would be permanently burned intothe tube and would be seen in all subsequent use, evenafter the scene had changed. When devices are extrasensitive, as in the case of low-light equipment,something as simple as a flashlight shined directlyinto the lens can cause damage. Using a CCD camerain this type of situation helps prevent damage.


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CCD cameras designed for use in extreme low-lightconditions (approximately 0.05 lux and below2)usually have a device called an intensifier built infront of the CCD array that multiplies the incominglight for the CCD chips behind it. Modern intensifiertechnology exhibits the same propensity to burn-in asvideo pickup tubes, however. Note that in this case itis the intensifier and not the CCDs that exhibit thistendency.

The method of intensification enjoys widespread usebecause the use of CCDs keeps the cost of the low-light camera below that of a video tube typeimplementation, gives it ruggedness and durability,provides freedom from frequent calibrations, andallows it to be used in a wider variety ofenvironments. If the intensifier were subjected toexcessive light and had some image burnedpermanently into it, the replacement cost for thecamera would be considerable.

Low-light intensified cameras can be found in a widevariety of price ranges. Such devices range fromattachments for existing cameras to full-blownamplified-light surveillance systems, with the qualityand sensitivity of the device depending on the cost.Given they can be used in rooms that would lookcompletely dark to the human eye, a very sensitive(therefore, very expensive) camera may be a smallprice to pay for law enforcement or surveillanceapplications requiring this capability. Regardless, themore typical application would be a poorly lit room ornight-time city scene, in which case a nominalsensitivity of 0.1 lux or more would be sufficient forgathering evidence or performing general, fixed, ormobile surveillance. Cameras claiming suchsensitivities are generally monochromatic (black andwhite), and do not employ the intensificationtechnology. They are significantly less costly thanintensified light cameras, making them a veryattractive choice in many applications.

Some practical examples are helpful to consider whendeciding between these two low-light cameratechnologies. A standard low-light camera wouldprobably enable a car’s front license plate to be read atnight, even though the car’s headlights were on. Alow-light intensified camera probably would not. Inaddition, the intensifier would probably be burned andneed to be replaced at a cost of around $4,000. If avery dimly lit warehouse required surveillance, a low-light intensified camera involved in that surveillancecould be severely limited, if not altogether disabled,by one very bright flashlight aimed at the camera’slens.

3.2.6 Infrared Cameras

Infrared cameras use special pickup devices that aresensitive to light with wavelengths longer than thosevisible to humans. Within this category, there are twotypes of equipment: thermal imaging systems andnear-IR systems. Both systems can be used in anenvironment that is totally dark to human eyes butwell illuminated from the camera’s perspective. Thisperspective changes, depending on the category ofequipment.

Thermal imaging equipment is commonly used by themilitary for night action. The image it forms is basedon heat emissions from the subject it is pointed at.The higher the temperature of the subject, the brighterthe image. This requires no special illumination butdoes require that your subject be a different tempera-ture from the background. Thermal imaging systemsare fairly expensive, ranging from $5,000 to $40,000.

Near-IR cameras use a special light source toilluminate the subject area. While subjects may be intotal darkness, the special light source makes thescene appear bright-as-day to the camera. This speciallight source, an infrared light, often will be providedwith an infrared camera but can also be purchasedseparately. Near-IR cameras with an accompanyinglight source range in price from $700 to $1,500.

2 Section 4 will explain “lux” and present examples ofdifferent lux levels.


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Some caution must be used in the selection of aninfrared light source. As wavelengths approach thered end of the visible spectrum (700 nm), it might bepossible for some humans to perceive the emittedlight. Therefore, it is desirable to have an infraredsource with a wavelength of more than 800 nm.

3.3 Camcorders and Recorder/Players

3.3.1 Video Tape Technology

Of the many video formats, VHS is the most popularin the world today. Since the format’s introduction in1975, the popularity of the VHS system has grownsuch that more than two-thirds of the households inthis country contain at least one piece of VHSequipment. The VHS format’s primary advantage isit is the lowest cost option for video. However, beingthe least expensive format has its trade-offs: at 240lines, it has the lowest horizontal resolution of theavailable formats. (Resolution and other importantperfor-mance parameters are explained in section 4 ofthis guide, called “Quality Parameters and the User –Interpreting Manufacturers' Specifications.”) TheVHS format has also produced some variants, whichare on the market today. Included in these are VHS-C,Super-VHS (S-VHS), and Super-VHS-C (S-VHS-C).

The “-C” designation implies that the system iscompact. To achieve this, the system uses a smallercassette. The -C format is used almost exclusively incamcorders because size and weight have a significantimpact on the camcorder user. Camcorders have beenproduced with this format that weigh less than 2 lb.The smaller cassette employed by -C systems still usethe same size and type of VHS tape, but the smallercassette only holds approximately one-sixth of theamount of tape that a “normal” VHS cassette holds.The amount of information recordable on a tape isreduced accordingly. The small cassettes are playablein a standard VHS machine with an adapter.

The “Super” designation indicates the same tape sizeand cassette as VHS format but uses newer recordingtechnologies to dramatically improve picture quality.Super VHS equipment have a greater signal-to-noise

ratio and a higher resolution (400 lines) than the plain(240 lines) VHS. Tapes recorded in standard VHSformat are playable on Super VHS machines, butSuper VHS tapes recorded in S-VHS format are notplayable on standard VHS equipment. (S-VHS tapesrecorded in VHS mode may be played back in eitherVHS or S-VHS players with the 240-line VHSresolution).

For several years after its introduction in 1974, theBeta format was thought to be superior to VHS. Asfar as resolution was concerned, that was true: Betaformat has a resolution of about 260 lines. On otherfronts, however, Beta was not superior. Sony optednot to license the format to other manufacturers, whilelicenses to produce VHS equip-ment were readilyavailable. The availability of a var-iety of equipmentled to a greater variety of prerecor-ded VHS materialfor public use. This drove the pop-ularity of VHS upwhile decreasing that of Beta. Eventually, marketforces led to an almost total stop-page of Betaequipment production. In spite of the dearth ofprogramming and the lack of mass market support,there is still a small market for Beta equip-ment.This, however, will continue to wane in the face oftechnology that is better and less expensive. Beta didmanage to produce one variation – ED-Beta (1985).This format improved on the resolution of Beta, butfailed to capture the interest of the market. Itsavailability in the United States is very limited.

One technology that is currently gaining ground in theconsumer marketplace is 8 mm. This technology,introduced in 1985, uses a cassette that is about thesize of an audio cassette, yet will hold a full 2 h or 4 hof video information. The resolution of this format isapproximately 300 lines, somewhat better than thatoffered by VHS. Like VHS-C, the most common usefor this format is in camcorders. Also like VHS-C,camcorders using this format have been producedweighing less than 2 lb. A possible disadvantage of8 mm, when compared to VHS-C, is the 8 mm tape/cassette format is incompatible with any VHSequipment. However, if the recording device, oranother 8 mm camcorder or VCR system is available,the tape will be playable through that device onto any


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NTSC television or monitor. The tradeoff betweenavailable recording time and compatibility has causedacceptance of the 8 mm format to grow slowly.However, the installed base of 8 mm equipmentappears to have reached critical mass, as new home-based 8 mm equipment is becoming available atprices only slightly higher than those available forVHS. The only existing variation on this format isHi-8, which has all the features of standard 8 mm, butthe resolution increases to approximately 400 lines.Like Super VHS, tapes recorded in standard 8 mm canbe viewed on Hi-8 machines, but tapes recorded inHi-8 format cannot be viewed on standard 8 mmequipment.

A format introduced in 1982 that had sufficientquality for use in some field production work isBetacam™. Betacam™ was phased out when a vastimprovement was made on this system in 1986 withthe introduction of Betacam™-SP. This changeincreased the resolution from 320 lines toapproximately 450 lines. This format is currently verypopular among circles where quality is veryimportant, such as television field production, and isused extensively in studios. Panasonic has aproprietary format that is roughly equivalent toBetacam™, called MII™.

The final analog format under discussion is C. Thisformat is for absolute top-of-the-line NTSC analogvideo. It provides more than 600 lines of resolution.It is the only major format that uses a reel-to-reel tapeinstead of a cassette. This technology makes theequipment rather bulky, but the size would beacceptable for use in surveillance vans. The bulk alsoprohibits the use of the C format in camcorders andtherefore requires the use of a separate camera unit.There is, however, a price to be paid for the quality ofC format – the equipment is very expensive.

Recently, digital video recorders, cameras andcamcorders have been introduced. Professionalequipment is currently divided into two camps: Sonyand Panasonic. Sony currently has five digital formats(D1, D2, Digital Betacam™, Betacam™ SX, andDVCAM™) and Panasonic has three (D3, D5, and

DVCPRO™). Resolution of digital cameras isgenerally at least 400 lines. Figures 9 and 10illustrate a typical digital camcorder and some of thecontrols one might expect to encounter.

Table 5 offers a list of video formats available forvideo surveillance equipment, the resolutionassociated with those formats, and the price ranges forequipment represented under each of the formats. Theprice ranges include the prices for individual pieces ofvideo equipment, that is, for camcorders andrecorder/players, unless otherwise noted. (Forinstance, for the VHS-C format, there are no VHS-Cplayer/recorders on the market. VHS-C cassettes areplayed in normal VHS player/recorders with anadapter. The figures in the price range reflect theprices of VHS-C camcorders only).

3.3.2 Camcorders and Video Recorder/PlayersFeatures

Camcorder and video recorder/player products offera vast number of features. Many of these are wellknown, while others are not obvious, and are thereforenot considered very often. Some of these "subtle"features may be just what are needed for certain kindsof surveillance applications. A number of thecommonly advertised features are briefly explainedbelow, along with some of those receiving lessattention.

Auto/manual focus: Automatic focus will change thefocus based on the perceived target and maintain ituntil something changes. Even if auto focus isavailable, professionals often will use manual focus incases when there is a chance that automatic featurewill have trouble differentiating the target from otheractivity.

Auto/manual white balance: Automatic white balancewill maintain the optimum color balance in eitherindoor or outdoor conditions. Manual control isuseful if unique conditions exist that the auto whitebalance feature cannot deal with (e.g., strongbacklight).


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Figure 9. Left side of a typical digital video camcorder

Auxiliary microphones and jacks for specialapplications: Many camcorders will accommodate theuse of auxiliary microphones if the built-inmicrophones are not adequate for special applications.A desirable characteristic of some camcorders is theexistence of a separate jack for the auxiliarymicrophone. With the jack, it is not necessary toremove the basic microphone from the camcorder.This keeps that microphone stored on the camcorderand eliminates the chance of it being misplaced.Wireless microphone sets, like the Vivitar WMK-2Wireless Mike Outfit, transmit over radio frequenciesfor hundreds of feet and are capable of transferringclear audio through typical doors and walls.

Battery type: The ability to use batteries allowsportability. Equipment might use rechargeablebatteries (e.g., nickel-cadmium or lithium-ion) orsingle-use batteries (e.g., alkaline). See NIJ Guide200-98 for more information on batteries.3

Book mark search: With this feature, one may returnto the point where recording had previously ended.

Day/time setting: A built-in calendar and clock allowseach recording to be “stamped.” A “button cell”battery keeps the date and time correct.

DV in/out jacks: Many digital camcorders have aspecial jack for digital video input and output. Theseinput and output signals are most frequently based onIEEE Standard 1394, also known as “FireWire.”Personal computer interface kits can be purchasedfrom both Sony and Canon that will allow digitalvideo to be downloaded from one of these camcordersto a PC.

Edit controller interface: LANC is the most widelyavailable interface for camcorders.

Fade control: When this control is activated, thepicture in the viewfinder of a camcorder and on thetape will fade out. When the control is disengaged,the picture will automatically fade back in.

3NIJ Guide 200-98 and other NIJ guides can be ordered fromNIST/OLES , 100 Bureau Dr., Stop 8102, Gaithersburg,Maryland, 20899-8102.


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Figure 10. Right side and rear of a typical digital video camcorder

Flying erase head: Allows user to make exceptionallyclean edits of the video tape. Video and audio“dubbing” (i.e., changing) is possible.

Headphone jack: Usually a 1/8 in stereo phono jack.

High speed shutter switch: Allows the camcorder tocapture and record high speed activities for slowmotion or still playback. Speeds might include1/250 s, 1/500 s and 1/1000 s.

Image stabilization: Optical or electrical.

Index search: An index mark can be placed at thebeginning of each recording so that automatic reviewand playback can be accomplished easily.

LCD monitor: Provides viewfinder information in alarger screen so camcorder does not have to be held tothe eye. Typical sizes range from 2 in to 4 in, color orblack and white. Figure 11 illustrates a camcorderwith both LCD monitor and viewfinder.

Light source: Built- in or accessory.

Macro control: This is used to unlock the zoom lenson a camcorder so that it can be used to get in-focusclose-ups of subjects normally too close to shoot.


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Figure 11. Example of a camcorder with both aviewfinder and an LCD monitor

Motion sensor: Useful for situations requiringconstant surveillance but where a low activity ratedoes not justify constant recording. Motion sensoractivates recording function. Audio sensors are alsoavailable.

Table 5. Price Ranges for Various VideoSurveillance Equipment Formats

Video Format Resolution(Lines)

Price Range Note

VHSVHS-CSuper VHSSuper VHS-C

240240400400

$200-$5,000$700-$1,500$900-$6,500

$1,200-$3,500

1

1

BetaED-Beta

260400

$2,000-$3,500$2,500-$4,000

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8 mmHi-8

300400

$700-$2,000$1,200-$3,500

U-matic 300 $4,000-$15,000 2

Betacam™Betacam™-SP

320450

N.A.$15,000-$40,000

C 600 $40,000-$160,000 3

Digital ComponentD1D5, MIIDigital Betacam™Betacam™ SXDVCPRO50DVCAMDVCPRO

700700600600500450450

$120,000-$180,000$50,000-$70,000$25,000-$51,000$23,000-$48,000$9,000-$50,000$4,000-$20,000$5,000-$30,000

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3

3

Digital Composite

D2

D3

600600

$40,000-$90,000$45,000-$55,000

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Mini-DV 400 $800-$5,000 1

Notes: 1. Includes price of camcorders only.

2. Beta and U-matic formats are not recommended for new equipment purchases because of the short projected support lifetime of these products.

3. Includes price of player/recorders only.

Multiple heads for still frames/slow motion playback:Video head design is an area where significantimprovements have been made in the past 5 years. Insimple systems, one video head is required to recordand playback the video track. Multiple heads have

been added to improve quality at different speeds,with some units automatically switching the outputfrom head to head to maximize the amount of signalthat can be recovered from a tape. As a result, noise-free still frames and slow motion effects can beproduced. It is also possible to have less noise (snow)in the picture scan mode.

Multiple start/stop buttons for diverse operatingconditions: Some camcorders have more than one“start/stop record” button – the Ricoh R800 forinstance. One button is found in or near the grip andthe zoom switch. The other button is located on ornear the lens barrel, for use when the camera is in alow position and a normal grip is impractical.

Noise reduction: Improves the picture quality inmarginal lighting situations.

Optical and digital zoom: Many camcorders,especially digital camcorders, provide a combinationof optical zoom and digital zoom. Optical zoom is thetraditional method of providing zoom lens capability.It is achieved through rearranging the distancesbetween some of the optical elements of the lens. Asthe magnification of the subject increases, generallythe camcorder loses some of its light sensitivity.Digital zoom is achieved by expanding a small area ofthe image pickup device (specifically a CCD) to fill


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the whole screen. This generally results in a loss ofimage sharpness and/or resolution.

Photo mode: Usually available on digital camcorders,less frequently on analog models. This feature allowsa single frame of video to be recorded across severalseconds of tape.

Remote controls: Typically using wireless technology,remote controllers can start and stop recording andeven control zoom functions.

Self timer/time-lapse recording: Self-timers are anattractive feature for surveillance that involvespredictable patterns. Camcorders and recorders canbe programmed to start and end at a certain time, or torecord only 1 s each minute for several hours.

Sensitivity/gain-up controls for shadows: “Sensitivity/gain-up” controls or buttons are intended to increasethe brightness in scenes that need it. The bettersensitivity mechanisms have made shadowed images50 percent to 80 percent brighter with little increase innoise or distortion (graininess in the image).

Special effects (Special FX): Examples include fades,wipes, solarization and posterization. These functionsproduce interesting visual effects but are probably notvery useful for surveillance applications.

Tape and time counter: Displays a number reading forthe position on the tape or the elapsed time during arecording. Time remaining may also be displayed.

Wireless playback: Using wireless technology (e.g.,infrared transmission), camcorder recordings areplayed back using a display that has an appropriatereceiver (typically supplied) for the wirelesstransmission.

Titling: Annotations of various lengths and types canbe added to the tape.

3.3.3 Camcorder Accessories

In addition to the features that come directly with acamcorder, other accessories can be purchased that

make the tedious and difficult operational tasks of thecamcorder a little more tolerable. A few are listedbelow. Others are available where video equipmentis sold.

Supports

Even with a small camcorder, it is a chore to hold it infront of you for any period of time. Fortunately,certain devices are available to help you carry yourcamcorder. One such device is called SteadyCam™,and another is called Glidecam™. These units havea harness that attaches the camera and steadyingmechanism to the body and an arm that holds thecamera out in front of you and swings to the side. Theuser has both hands free to manipulate the camera orcamcorder. The price of such an equipment aid variesfrom about $200 to about $4,000, which may be welljustified if several hours of “hand-held” video tapingis needed.

Another type of support is a basic shoulder mount.This kind of item comes with a padded shoulder restand handle and costs about $200. The tripod mountof the camcorder is attached to the product whichallows the camcorder to be adjusted back and forth tosuit the user's eye position. Some may find thisdevice awkward to use and somewhat lesscomfortable than a harness system, especially if thecamcorder is long or front-heavy. An example of ashoulder mount product is the Videosmith’sMightyWonderCam™.

The conventional tripod is yet one more type ofsupport product. Unfortunately, many of the sturdytripods tend to be bulky and awkward to carry. Anumber of products on the market, however, includingthe Cullman Video Magic Tripod, use aluminummaterials and good folding designs so that units weighless than 3 lb and can be collapsed into a verymanageable 14 in x 6 in x 1½ in shape. The Cullmanproduct also includes a built-in monopod, a two-waypan head with handle that allows easy and fluidpanning. The Cullman unit has a manufacturer’ssuggested retail price of about $200.


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Auxiliary Monitors

Most camcorder viewfinders are quite small in size(about an inch square) but provide the user with arelatively good image of the scene in view. At thesame time, they can provide much data about thecurrent operation of the camcorder (e.g., timeremaining on the tape, manual or auto settings, andbattery condition). With all of those data appearingand the necessity to concentrate on the scene to berecorded, some users may prefer to deal with a largerdisplay. Some camcorders come with larger displaysin addition to or instead of the traditional viewfinder.For those camcorders that do not have a larger displaybuilt-in, auxiliary monitors, which fit on the accessory"hot shoe" found on many camcorders, offer one wayto see a larger color image of the scene. They alsoallow the user to review camera settings and statuswithout constantly glancing down into the viewfinder.One such monitor is the Citizen LCD Color Monitor.It weighs only 6.3 oz, has a 3 in diagonal screen, andcan be powered by AA batteries (for 3½ h), batterypack, or AC.

Environmental Enclosures

To expand the utility of camcorders, many companiesoffer environmental enclosures for cameras andcamcorders. These range from simple rain covers tounderwater enclosures. Rain covers vary in pricefrom $50 to several hundred dollars, depending onmanufacturer, degree of protection, and features(some come with heaters!). Underwater housingsvary in price from $600 to several thousand dollars,depending on manufacturer, depth rating, andcamcorder model.

Video Capture Cards

With the advent of “multimedia computing,” a largenumber of computer interface devices have becomeavailable that allow video to be imported into acomputer for inclusion in reports, presentations, andto be printed on computer printers. The devices arevaried and command a wide range of prices. At the

bottom end is the Snappy Video Snapshot, a devicethat hooks to a computer’s printer port and converts acomposite analog video frame to a computer image.More elaborate systems include cards that plug intothe expansion slots inside the computer. These cardsmight have video input/output jacks and record fullmotion video to the computer’s hard drive (e.g., DataTranslation Broadway Beginner).

For digital camcorders with a DV interface, there arespecial kits available from the manufacturers of thedigital camcorders to allow easy download of thedigital video from the camcorder to a personalcomputer. One example is the Canon Video DK-1DV Capture Kit. The kit includes an IEEE 1394interface card for the computer; a cable to connect thedigital camcorder to the computer; and software tocontrol the digital camcorder, download images, andsave the images to disk.

3.3.4 Format Applicability to SurveillanceRequirements

Following are several tables that provide informationon what type of equipment would be applicable tospecific surveillance conditions. The equipmentrecommendations conveyed in the tables are orientedtoward the need to perform real-time informationcollection. Equipment not meeting theserequirements are not shown in the tables. Forexample: while a monitor/television is required todisplay information on a videotape, it is not necessaryto be able to view the tape in great detail at a crimescene. However, for some surveillance applications,such as where a high power or amplified light lens isbeing used on a camera, a monitor may be necessaryto make sure the subject is being properly recorded forlater presentation (e.g., in court).

Table 6 provides a list of video equipmentapplications along with recommendations on whatequipment types would produce meaningful videodata. Table 7 provides a bit more focused detail byrecommending equipment based on specificsurveillance performance requirements.


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A note of clarification regarding table 7 is in ordersince standard VHS and 8 mm equipment wasgenerally not recommended because of its lowerquality (i.e., resolution). Higher-resolution SuperVHS and Hi-8 equipment is now widely available atreasonable prices. If, however, cost is the mostimportant factor in the decision of what equipment topurchase, the standard VHS and 8 mm formatsshould produce moderate results for any performancerequirement where Super VHS and Hi-8 is specified.

Another consideration when determining whatequipment will meet a performance requirement islight level. In all cases, camera resolution drops whenlight drops. The lowest light level in whichmanufacturers claim their cameras can acceptablyrecord a scene varies from as high as 30 lux to lessthan 1 lux. Thirty lux corresponds to the lightingexpected in an underground parking garage, and 1 luxwould be equivalent to a medium sized dining roomlit by two or three candles. It is the 1 lux rating ofsome of the camcorders available on the market thatallowed them to be included as a possibility formeeting performance requirements in dim lightingconditions.

3.4 Monitors/Televisions

3.4.1 Technology Summary

Since computers and video equipment both usemonitors, one might conclude that a computer monitorshould work with a video camera system, right?However, this is not the case. Computer displays

have a different function than the video displays usedfor industrial or broadcast video. The video systemsused throughout the world for such purposes asrecreation, news, education, and surveillance weredesigned and implemented to broadcast movingpictures. Motion tends to make humans focus theirvisual attention (and their need for sharpness) in thecenter of the screen, with the corners and edges of thescreen treated as only a secondary concern. Videosystems display objects that people recognize in reallife. They also count on people to "help the imagesalong" by using their experiences to fill in lackingdetails and color as required. This is often neededbecause video systems that people are most frequentlyexposed to, such as television, are medium-resolutionblack and white systems with a low-resolution colorchannel overlaid on the black and white image. Eventhe “high-definition” television (HDTV) systemsproposed as the next generation of TV (that will haveabout twice the resolution of existing systems) willcontinue this approach.

Computer systems display static images of detailedinformation, such as words or numbers. Pictureelements (pixels), which can be thought of as littledots of light, are grouped in patterns to form the lines,letters, words, numbers, and other symbols seen on acomputer monitor. Information found in the cornersand on the sides of a computer monitor is just asimportant as that found in the center of the screen.The graphics created by computers and their displays,although much improved from just a few years ago,still do not perfectly reflect natural things but tend tobe abstract.


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Table 6. Surveillance Applications and Recommended Equipment

Surveillance Application Recommended VideoTape Formats1

RecommendedEquipment Types2

Building/area access V,S,8,H,F C,T,M

Building/area security V,S,8,H,F C,T,M

Operation/protective detail coordination S,H,B,C,D,E,F C,T,M

Crowd monitoring V,S,8,H,F C,T,M

Monitor officer on routine stops V,S,8,H,F C,T,R,M

Monitor officer/suspect in dangerous situation S,H,F C,T,R,M

Monitor confinement areas V,S,8,H,F C,T,M

Record bomb squad V,S,8,H,B,D,E,F C,T,R,M

Record crime scene V,S,8,H,B,D,E,F R

Record forensic data V,S,8,H,B,D,E,F R

Record interrogations/polygraphexaminations

V,S,8,H,B,D,E,F C,T,R

Record physical evidence V,S,8,H,B,D,E,F R

Search and rescue S,H,B,D,E,F C,T,R

Airborne surveillance S,H,B,D,E,F C,T,R,M

Indoor surveillance S,H,B,D,E,F C,T,R,M

Outdoor surveillance S,H,B,D,E,F C,T,R,M

Vehicular surveillance S,H,B,C,D,E,F C,T,R,M

Video mug shots V,S,8,H,F C,T,R

Notes for Table 6:

1. Video Tape Format abbreviations: C = C; V = VHS and VHS-C; S = Super VHS and Super VHS-C; 8 = 8 mm;H = Hi-8; B = Betacam™, D = Digital Component, E = Digital Composite, F = Mini-DV. Beta and U-maticformats are not recommended for new equipment purchases because of the short projected support lifetime ofthese products.

2. Equipment Type abbreviations: C = Cameras; R = Camcorders; T = Video Tape Recorders; M = Monitors and Televisions.


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Table 7. Equipment Recommendation for Various Surveillance Resolution Requirements

Surveillance Resolution Requirement Recommended VideoTape Formats1

RecommendedEquipment Types2

Facial ID at more than 200 mDaylightDim lightDarkness

B,C,D,EB,C,D,EB,C,D,E

C,T,MSpecial3

Special

Facial ID at 50 m to 200 mDaylightDim lightDarkness


C,T,MSpecialSpecial

Facial ID at less than 50 mDaylightDim lightDarkness

S,H,B,C,D,E,FS,H,B,C,D,E,FS,H,B,C,D,E,F

C,T,R,MR,SpecialSpecial

Figure ID at more than 200 mDaylightDim lightDarkness


C,T,R,MSpecialSpecial

Figure ID at 50 m to 200 mDaylightDim lightDarkness

S,H,B,C,D,E,FS,H,B,C,D,E,F

B,C,D,E


Figure ID at less than 50 mDaylightDim lightDarkness

S,H,B,C,D,E,FS,H,B,C,D,E,FS,H,B,C,D,E,F


Notes for Table 7:1. Video Tape Format abbreviations: C = C; V = VHS and VHS-C; S = Super VHS and Super VHS-C;

8 = 8 mm; H = Hi-8; B = Betacam™, D = Digital Component, E = Digital Composite, F = Mini-DV. Beta and U-matic formats are not recommended for new equipment purchases because of the short projected support lifetime of these products. 2. Equipment Type abbreviations: C = Cameras; R = Camcorders; T = Video Tape Recorders; M = Monitors and Televisions. 3. Special implies that the equipment required to perform this function is highly specialized, such as low-light and low-light intensified cameras.


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The difference in applications between computer monitorsand video monitors will help explain the rationalebehind the basic technical design of videomonitors/TVs and why computer monitors would notwork very well for video applications (even if theinterfaces were compatible). Note that video monitorsand televisions are considered to be essentially thesame in this discussion, since the way video isformed, transferred, and received is fundamentally thesame for both. To be more explicit, the monitor islike a TV receiver, with the picture tube andassociated circuits but without the rf (radio frequency)tuner and if (intermediate frequency) section. A truemonitor does not have antenna input connections toreceive radio broadcasts but receives video from othersources via video input jacks. Several products are onthe market that are combination monitor/televisions.Dual sets of connectors allow either TV or monitorapplications.

The ability of a video monitor/TV to resolve an image,that is, to show the detail of the image, is limited bytwo bandwidth restrictions – approximately 4.7 MHzfor the luminance (black and white) and 1.5 MHz forthe chrominance (color) portions of the picture.These bandwidth figures apply to the RS-170A videostandard used in the United States to define NTSCvideo (color television). The speci-fications werechosen to conserve radio frequency spectrum for thebroadcast services, and because of the limitations oftelevision technology at that time. These bandwidthlimitations still apply regardless of how well theequipment is designed and built.

(Computer monitors, by the way, have a much widerbandwidth, typically from 20 MHz to 100 MHz. Noreal standards restrict the design of computermonitors; only technological and economic factorsapply. With virtually an unlimited amount ofbandwidth available, computer displays can show atremendous amount of detail.)

For monitors, usually color is fed through 3 separatesignals - red, green, and blue - with identicalbandwidths. (The red, green, blue signals are wherethe acronym "RGB" comes from in video literature.)Picture tubes used in computer displays have a much

smaller, highly-focused electron beam spot size andfiner pitch screen surface than most videomonitors/televisions.

Besides video bandwidth, another technical parameterthat affects the “\definition, or the quality of detail ona display screen, is scan rate. The video picture isscanned in a sequential series of horizontal lines, oneunder the other, to permit one video signal to includeall the elements for the entire picture. In effect, videopictures are reassembled line after line and frame afterframe. For NTSC video, a total of 525 lines arerequired for the development of one picture (frame).All 525 lines are scanned in 1/30 of a second.

The higher the horizontal scan rate and videobandwidth, the higher the resolution. In addition, fora given horizontal scan rate, as the vertical scan ratedecreases the level of detail increases because thereare more horizontal lines used to make a completeimage. Like the bandwidth, scan rates for NTSCvideo are specified in much detail in the RS-170Astandard. The broadcast standard mandates ahorizontal scan frequency (rate) of 15,734.263 Hz.This number is commonly referred to as 15.75 kHz.The vertical scan rate is fixed at 59.94 Hz and isnormally called 60 Hz. For comparison purposes,computer monitors have horizontal scan rates between15 kHz and 100 kHz. (Once again, no standardsrestrict the rate.) At 75 kHz, the computer monitor isalmost five times faster than the video monitor.

Vertical scan rates for computer monitors run fromabout 40 Hz to 120 Hz, but many of the video cardsavailable for computers today start with a defaultvertical scan rate at or around 60 Hz. This is acompromise between having the lowest possiblevertical scan rate and having problems with peopleviewing the screen. Vertical scan rates below 60 Hzare somewhat of a problem for humans. If the scanrate is not fast enough to prevent the light emissionfrom the phosphors in the display from decaying toofar, the resulting variations in the brightness of theimage can be seen. The varying brightness isperceived as a definite flicker.


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With all of the constraints placed on video, it is nowonder that some people have compared the bestresolution possible for a video monitor and acomputer monitor to the difference in picture qualitybetween a newspaper and a magazine, respectively.Nevertheless, beyond its image detail (resolution), afew more picture quality measures can be used todescribe a good monitor’s performance. Assuming itis synchronized to stay still, a color or monochrome(black and white) monitor’s reproduced picture shouldalso have high brightness, strong contrast, and thecorrect proportions of height and width (aspect ratio).Also, color sets should have strong color, or“saturation,” with the correct tints or hues.

3.4.2 Monitor/Television Features

As mentioned above, many of the characteristics ofvideo monitors and televisions are fixed by arecognized NTSC standard so that video broadcastsmay be received equally well by all. Even so,monitors will be offered with various ratings forquality parameters as basic as resolution. Resolutionfor monitors/televisions will range from 200 lines to300 lines4 for inexpensive models found in the hometo units with 400 lines or 500 lines for those withdiscriminating (and expensive) taste. Units with 800lines to 1,000 lines are used in television broadcaststudios. One way to gauge the resolution needed fora particular application is to be aware that the bestresolution one can expect from over-the-air broadcastor cable TV service is 330 lines. If a "good" TVpicture will suffice for a certain task using a monitor,it is not necessary to select one with more than 330lines.

Other featured items to be aware of whencontemplating monitors include:

Screen size: Measured diagonally, this can varydramatically. Typical sizes run from about 8½ inthrough 20 in, but super-small and huge monitors areavailable, also.

Color or black and white presentation: Both areavailable at many resolution ratings.

Built-in speaker, jack for external speaker, headphonejack: Allows audio monitoring publicly or privately.

Selectable inputs: BNC-type coaxial cable and/or 8-pin video jacks for composite and RGB video areavailable. Switchable line, camera, and VCR inputjacks may also be offered.

Monitor bridging: Selectors and connectors allowbridging to display video on multiple monitorssimultaneously.

Synchronization signal: External input and outputsynchronization interfaces for when synchronizationwith a separate video device is required.

Front panel controls: Include brightness, contrast,vertical hold, horizontal hold, tint, and color.

Blue-only control: This displays only the blue electronbeam for simplified adjustment of chrominance andhue using a color bar signal.

Comb filter: Integral to a monitor’s design, a combfilter minimizes loss of resolution and reducesstreaking and wavy edges on fine patterns.

Remote control: Wireless.

Input power: 120 VAC and DC versions are available.

Mounting options: Rack mountable.

Carrying handle: Folds down when not required.

Enclosure: Metal cabinet and magnetic shield ringreduces interference from other electronic equipment.

4The resolution of NTSC video equipment is measured by thenumber of vertical lines that can be distinguished(horizontally) across a frame of video. This is because (1)vertical resolution is fixed and (2) one gets an indication ofhow much information the frame contains, regardless of thesize of the input or viewing device.


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3.5 Special Surveillance Systems

3.5.1 Specialized Camera Systems

In recent years, the electronics industry hasrevolutionized the video camera industry. Use ofCCDs and integrated circuits have allowed aconsiderable reduction in the size and cost of videocameras. One product that is available is called a“board camera.” This camera consists of the CCDand other electronics on a 1.5 in square (or smaller)printed circuit board with a lens mounted over theCCD. Because of their small size, they are easilyconcealed. Some examples of places these camerascan be concealed include ties, hats, jacket lapels,brooches, books, cigarette packs, smoke detectors andbriefcases. Power is supplied by an external devicesuch as a transformer or battery pack. The videosignal is usually fed to a monitor, video recorder, orvideo transmitter.

3.5.2 Patrol Car Surveillance Systems

Patrol car surveillance systems are special video (andaudio) equipment ensembles that were designedspecially for police applications. Originally conceivedto be that silent partner for individual officers onpatrol, the applications for these systems haveexpanded beyond officer safety. Not only do thesesystems provide a clear record of faces, vehicles,license numbers, weapons, and the conversations thattranspired before and during dangerous situations (sothat back-up can be called in), but videotapedocumentation of routine occasions has also beenfound to be valuable. Videotapes have been criticalevidence in allegations and liability suits againstpolice and have been used extensively in contestedarrests, particularly drunk driving cases. In addition,video and audio tapes from patrol car surveillancesystems can be used as training tools for new officers(or experienced officers) to insure proper procedureand caution are exercised under variouscircumstances.

A typical patrol car surveillance system consists of acamera, control and status panel, recorder (either8 mm or VHS tape format), protective case for the

recorder, and wireless microphone. The camera ismounted on the inside of the police car's frontwindshield. It is a digital CCD black and white orcolor camera that normally can operate across a wideillumination range (from low light provided byheadlights to bright sunlight). An auto iris lensadjusts the light level from day to night viewing,while a polarizing filter is used to reduce reflectedglare. Since the camera has been designed for thepolice application, it is small, lightweight, andresistant to vibration and shock. A wide-angle lens(e.g., 8.5 mm to 15 mm) allows the camera to view anextended area.

The control and status panel is located near the officerin the car. It may be installed next to the radio, forinstance. This unit allows the officer to turn thesystem on manually or to have the system come onautomatically when the overhead flashing lights areturned on. The recorder stops when the officer selectsthe off control. The unit also indicates the status ofthe recorder and the microphone. A display light orother type of warning is given when the recordingtime is nearing or at its end. A VHS tape records upto 6 h of video and sound; a 8 mm tape can record 2 h.

The recorder, in an environmentally controlled,fireproof, bullet-resistant case, is usually located inthe trunk of the vehicle. Heat or cooling is providedinto the case when thermal switches detect a need.Limited access to the trunk and into the recorder case(it can be padlocked) helps protect the tape fromtampering and preserves its integrity as evidence incourt. The recorder itself cannot be removed (evenfor playing back tapes).

A tiny wireless microphone, used in conjunction witha pocket-sized transmitter and antenna, allows thesurveillance system to hear sounds around the officer,especially when he/she leaves the patrol car. Themicrophone can be attached to a lapel or tie and maybe provided with a wind-screen to greatly reducebackground noise caused by the wind. Thetransmitter and built-in antenna can be clipped to abelt or be kept in a pocket. The wireless microphonehas a range of about 1,000 ft (officer to car) undernormal conditions. Because its range is limited, a


29

radio license is not required for this transmittingsystem.

Another component of the police car surveillancesystem that may be offered is a video/audio monitor inthe car that can be used for continuous viewing andfor focusing and adjusting the camera. If it is notpractical, or too expensive, to install a monitor in eachpatrol car, one monitor may be used to focus andadjust the cameras of several (or all) surveillancesystems in a department.

An example of a patrol car surveillance system is theEyewitness™ system sold by Kustom Signals, Inc. ofLenexa, Kansas. A complete system is pricedbetween $3,900 and $5,500, depending on the type ofvideo tape format required (VHS or 8 mm). TheEyewitness™ system includes either a color camerathat has a minimum illumination of 5 lux and 300lines of horizontal resolution, or a black and whitecamera that can operate at 0.5 lux and 420 lines ofresolution. Both cameras can operate from 14 °F to122 °F. The selected camera is connected to either an8 mm or VHS video recorder that resides in a patented"vault" in the trunk.

3.5.3 Retractable Surveillance Systems

Designed to replace conventional overhead closedcircuit television systems, these specialized videosurveillance systems take many shapes and sizes.Some, such as the Knox Forward IntelligenceGathering System (FIGS), are in-ground/above-ground products designed for both industrial andgovernment applications. The FIGS camera headassembly can be buried in the ground, hung from apole or traffic light, or fitted into the recesses of abuilding. When activated, the camera head emergesbeyond the edge of its case to a desired height at orbelow 8 in. In its basic configuration, FIGS willconnect to most pan-tilt control drivers for full controlover its main functions (including vertical andhorizontal viewing, focusing, zoom, iris adjustment,and other auxiliary needs). Various cameras can beused with FIGS – a standard black and white CCD;

optional high resolution B&W CCD or color CCDcamera, or optional intensified day/night camera.

The control unit for FIGS is available in a waterproof,air-tight carrying case, and can control the cameraassembly unit via wire, or optional UHF radio controllink. Video information may be transported by wireor an optional microwave radio video link. For lawenforcement and military applications, FIGS can beobtained with a host of special electronics. For innercity surveillance, both data and video can betransmitted over dedicated phone lines using specialline drivers. FIGS can also operate over satellite.

Another Knox product that is similar to the FIGS, butfits well into another environment, is the Covert CarAntenna Video System. Details on this system, andothers, may be acquired through the manufacturer inGreenwich, Connecticut, or other makers of videosurveillance gear.

3.5.4 Portable Systems

If it is not possible to monitor an area from afar or ifsubjects frequently move from one location toanother, it may be necessary to go to where theinformation is. For just those occasions, undercoverattaché cases are available. One such case is made byESC. The internal components, which consolidate theimage and audio capturing and transmission functions,are cleverly hidden in a false top compartment of thecase leaving no visual clue as to their existence. Thetiny hole in the case, through which the cameraoperates cannot be seen even from as close as a footaway.

A 9 mm f/3.5 pinhole wide-angle lens isinterconnected to a CCD camera that has a minimumillumination rating of 3 lux, resolution of 280 lines,and a signal to noise ratio of 46 dB. A number ofvideo link options are offered that include UHF andmicrowave radio transmitters and matching receivers.The 1.3 GHz system also comes with a mini-dishantenna. All systems are powered by batteries that fitin the case.


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4. Quality Parameters and the User — InterpretingManufacturers’ Specifications

The most relevant technical parameters used tomeasure the quality of cameras, camcorders, videorecorders/players, and video monitors are described inthis section. There are very specific relationshipsbetween these parameters that engineers use to assessthe quality of video gear and what the typical usernotices when using the equipment. The explanationsof the performance parameters, therefore, contain“real world” information related to the humanperception process along with the basic definitions ofthe engineering terms. Once a user understands howa particular technical parameter will affect him duringvideo surveillance work, he can relate data from themanufacturers’ brochures and specification sheets tohis needs. Equipment selection and purchase thenbecomes easy.

4.1 Technical Parameters’ Relationship to Law Enforcement and Corrections Needs

In the earlier section on video surveillancerequirements, it was suggested that a large number ofspecific video needs for law enforcement andcorrections could be summarized into a short set ofgeneral requirements (e.g., identifying subjects,recording data) Table 8 shows how the numeroustechnical parameters that are used to describe thefunctional and physical characteristics of equipment,and to measure its quality of performance, correlate tothis fundamental set of police needs. That is, the tableindicates what parameters might be especiallyimportant to consider for certain applications. Inseveral cases, one parameter (e.g., resolution) can beseen as being relevant to more than one communityneed. (In fact, it can be argued it should be listedunder all need categories.) The table is not intendedto include all possible combinations under allconditions. Rather, it is intended to be a “jumping off

point” for users to contemplate when they start toreview what technical parameters are important tothem.

Table 8. Test Parameters’ Relationship to LawEnforcement and Corrections Needs

Parameters Needs

ResolutionSignal-to-noise ratioMinimum illuminationLens, max apertureTape speed/“record mode”Color accuracyFocusing accuracyAudio input levelAudio frequency responseSelf timerWireless remote control

Identifyingsubjects

Color accuracyFocusing accuracyMinimum focal rangeSpecial featuresAudio input levelAudio frequency responseSelf timerWireless remote control

Recordingforensic data

Zoom speedFocusing accuracyFocusing speedTime response-featuresShutter speedsResolutionSignal-to-noise ratioMinimum illumination

Multipleactivities

Operating temperature rangeOperating humidity rangePower requirementsPower consumption

Indoor/outdoorwork


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Table 8. Test Parameters’ Relationship to LawEnforcement and Corrections Needs (cont’d)

Parameters Needs

Electrical connectorsPhysical mountsAudio output levels

Flexibility

DimensionsWeightPhysical mountsOther human engr. aspectsUtility/accuracy of manualsTape lengthFast forward timeFast rewind timePower requirementsBattery charging timeTransportabilityScreen sizePower consumption

Operationaleffectiveness

The following section introduces the technicalparameters and explains their basic concepts. Thisbackground material should be helpful in tyingparameters to user applications and requirements.

4.2 Parameter Definitions

4.2.1 Resolution

The parameter most often quoted as being a reliablemeasure of quality is resolution, which is thecapability of a piece of video gear to distinguish,record, and/or reproduce the details in a scene. Thehigher the number of “lines,” or “TVL” (TelevisionLines), the greater the horizontal resolution of animage. A look at the method used to determine thenumber of lines is helpful in better understandingresolution.

The number representing the measured resolution isarrived at by first focusing a camera at a test pattern,which typically has alternating black and whitevertical lines of equal width. (A number of testpatterns may be present on a single chart.) By

situating the camera a certain distance from the chart,a pattern can be made to fill the entire view of thecamera. If the camera is connected to a monitor orTV, this is easy to do by simply observing the monitoror TV. If the camera is close to the chart, it is not toodifficult to find the number of lines filling the view ofthe camera simply by counting them on the monitor.

The number of lines seen by the camera can beincreased by moving the camera back away from thechart or by zooming back with the lens. If thisprocess is continued, there will come a point wherethe vertical lines are too close together for the camerato "resolve" them, that is, to see two neighboringwhite lines as being separated by a black one or twoneighboring black lines as being separated by a whiteone. Instead of alternating black and white lines, thecamera will begin to see a uniform, medium gray.Before this happens, the number of vertical linesacross the screen is counted, and this number is notedas being the "resolution" of the camera. Note that"240 lines of resolution" means that a device candistinguish, record, and/or reproduce at least 240 linesof resolution.

For the above test to work as described, the monitormust be of higher quality than the camera. If amonitor is being tested, the camera providing its inputmust be of higher quality than the monitor. For amore precise measurement of resolution, a high-quality digital oscilloscope with a televisionsynchronization option is used to view and measurethe electrical output of a camera. Lines can becounted automatically between two cursors markingthe edges of the test pattern's waveform.

Now that it is known that more resolution is betterthan less, how many lines of resolution are reallynecessary in a piece of video equipment? The answerdepends upon the application. Some examples mayprovide a rule of thumb. Three hundred thirty (330)lines of resolution is considered to be the quality limitof what can be received by broadcast or cabletelevision in the home. Two hundred forty (240) linesis the nominal figure for VHS or 8 mm video tapeformats. People notice that VHS and 8 mm tapeplaybacks do not resolve individual hairs on a person's

Quality Parameters and the User – Interpreting Manufacturers’ Specifications

33

head when the person fills the screen to the extent thata newscaster does at a normal distance (head andshoulders – referred to in the industry as a “talkinghead”). If the newscaster is viewed from a broadcast(“over the air”), much more detail may be visible, andindividual hairs probably will be noticeable. Super-VHS and Hi8, with common resolution figures of 400lines to 420 lines, definitely are able to resolve hairdetail at this distance. Higher quality studio-typeequipment, such as Betacam™-SP, and proposedHDTV broadcast, cable, and tape standards mayreveal even the pores on a person’s face at a “talkinghead” distance.

The bottom line for resolution is this: the higher theresolution rating, the easier it is to positively identifya suspect who is across a parking lot or street. Betterresolution also means the videotape played back incourt will show more detail. What really is necessarythough, since more resolution means more money?The answer can follow this rule of thumb. If the liveimage or recording has to be as good as the bestbroadcast or cable TV picture you have ever seen, atleast 330 lines of resolution are necessary. (Thatmeans Super VHS, Hi8, digital, or broadcast qualityin a camcorder.) If you can live with less detail inmost cases, select a VHS or 8 mm camcorder, or acamera, player/recorder, or monitor with fewer linesof resolution.

4.2.2 Signal-to-Noise Ratio

Electrical and electromagnetic signals are all aroundus constantly. They originate at both natural and man-made sources. Many of the signals provideinformation for us and are desirable at a particularpoint in time (e.g., we tune our receivers to findsignals broadcast from commercial television andradio stations). On the other hand, some signalemanations interfere with, or detract from, theinformation in the desired signals that we are trying toreceive. These signals are called noise.5 With any

type of telecommunications transfer involving audio(including voice), video, data, or multimedia (i.e.,combinations of audio, video, and/or data), it isimportant to maximize the desired signal (or signals)and minimize the noise to accurately receive theinformation. The signal-to-noise ratio, SNR, is ameasure of how well this has been achieved. TheSNR is the power of the desired signal divided by thepower of the noise signal.

During video surveillance work, a number ofinformation signals are transferred. For example, acamcorder takes video and audio informationcollected by its camera and microphone and records itonto a magnetic tape in its recorder. Similarly, astand-alone video camera passes visual information tothe tape of a separate video recorder or to a monitorfor viewing. If noise is present during any of thetransfers, the quality level of the video and audioinformation will be degraded. The tape will recordboth the desired and undesired signals, and themonitor will display the noise along with the video.Evidence of noise in video transmissions is theappearance of “snow” on the screen, which essentiallydilutes the video signal. Audio noise is commonlyheard as popping or hissing sounds. When noiselevels become too high (as compared to the desiredsignals), the video image will be completely lost in a“whiteout” or in a wash of distorted colors. The audioinformation will be indiscernible. In manyoperational settings, the level of noise will not changevery much over a certain time span. Therefore, if thesurveillance equipment on hand is not adequate toproperly capture and record the desired informationunder the conditions present, there is little theoperator can do.6 It is critical, then, that equipment beprocured with a signal-to-noise ratio that is sufficientfor prospective operational scenarios.

The developers of video equipment realize thedetrimental effects that noise can have on video

5 It is possible to have situations where desired signals forsome people become the noise source for other people andtheir systems.

6 If the operator of video surveillance equipment has somecontrol over the environment where the surveillance will takeplace, some improvement in SNR may be possible. That is,an increase in illumination (light level) will increase SNR (asexplained in the next section).


34

quality. Therefore, designs are employed thatinherently reduce the system’s sensitivity to unwantedelectrical noise. At the time of manufacture, noiseshielding may also be installed in areas of the productthat are still susceptible to noise degradations.Overall, different manufacturers use many techniquesand attain various levels of success as they attempt toprotect their equipment from noise. Unfortunately, itis not clear to the casual observer examiningequipment which products have the greater naturalimmunity to noise. The SNR specification, ifprovided, can be looked upon as an immunityindicator, however.

The lower the noise sensitivity (the higher the SNR),the greater the ability to get a quality image out of adevice at low light levels. But how is SNRquantified? The SNR is measured by putting a knownhigh-quality signal into a piece of video gear,recording what comes out, and comparing the outputto the input. Since some noise always gets into thesignal by the time it is output, measuring exactly howmuch noise was output can provide an SNR.

For cameras and camcorders, most specificationsheets will show SNR in "dB” at a recommendedillumination (light level). The abbreviation “dB”means decibels. Decibels in this case do not haveanything to do with the magnitude of sounds orloudness. Decibels simply express the logarithmicratio of two voltages, for the signal and the noise. Aratio of 6 dB (technically 6.02 dB) means the signal istwice the noise. For each additional 6 dB, the voltageratio doubles (e.g., 12 dB = signal 4 times larger, 18dB = signal 8 times larger). For 60 dB, the signal is1,024 times larger than the noise.

4.2.3 Minimum Illumination

Noise sensitivity is impossible to eliminatecompletely, so as the signal level drops (i.e., as thelight level of a scene drops) and the noise levelremains the same, the signal to noise ratio drops, andnoise will begin to appear in the picture. As the lightlevel continues to drop, the scene looks progressivelyworse. Although there is no point at which a picturesuddenly becomes completely unusable, there does

come a point where at least half of the people trying toview it would consider it too annoying to watch orwould be unable to discern facial or even other largefeatures easily. Somewhere before this point,equipment manufacturers are said to measure the lightlevel of the scene and claim that the video equipmenthas that certain minimum illumination requirement, alux level. In general, the color carriers and colorreceptors require more light to function properly, thusyielding significantly higher lux ratings than theaverage black and white camera. For example, a colorcamcorder's sales ad may refer to a "3-lux" camcorder,while a black and white camera’s sales ad may claimit is a 0.5 lux camera.

Unfortunately, these statements of minimumillumination leave plenty of room for confusion.First, the lux is not a common term amongAmericans; what does lux mean? Once lux isdefined, it is not straightforward to judge lux levels.Although a user can recognize that one camcorderpresumably needs less light than another to functionproperly, he cannot tell what the relative difference isbetween light levels (e.g., between 3 lux and 20 lux).Finally, the user does not know what quality can beexpected at a specified lux level.

Since lux is at the center of this discussion, it isimportant to get some feeling for what a lux is. Luxis a measure of illumination that is used within theInternational System of Units (i.e., the MetricSystem). A lux is defined as one lumen per squaremeter, where the “lumen” is a well-defined measureof light power. In other words, when a lumen worthof light is uniformly distributed across an area of onesquare meter, the light level of that area is one lux.The foot-candle is analogous to the lux but usesdimensions that are more familiar to Americans. Thefoot-candle is equal to one lumen per square foot.Since the light source is the same for both measures,the only difference between the values of lux andfoot-candles has to do with the areas of theilluminations (square meters and square feet). Withone meter equal to approximately 3.281 ft, one squaremeter equals 10.76 ft2. This means the illumination ofa foot-candle is more than 10 times brighter than thelux since the same amount of light is concentrated


35

over a much smaller area. One foot-candle equals10.76 lux.

But how does a user determine what his typical luxlevels will be? Like resolution, the answer comesafter thinking about the conditions in which videoequipment is likely to be used. Table 9 gives someaverage reference numbers for various outdoor andindoor conditions. These "rough" numbers can beused as rules of thumb from which to gauge typicalillumination requirements. In general, it appears thatoutdoor daytime applications and indoor applicationsthat have a normal amount of artificial lighting can beaccommodated by most off-the-shelf cameras/camcorders. Surveillance situations that occur atnight or in very dimly lit locations indoors will requirespecial, low-light cameras. True low-light camcordersare not available; however, some can be supplementedwith light amplifiers to achieve low-light capability.One example of this is the Astroscope series ofproducts from Electrophysics Corporation. Inaddition, some camcorder manufacturers (e.g., Sony,Panasonic) provide a feature in some of their modelsthat disable the color channel in low-light situations,therefore reducing noise and extending the light rangeof their camera. While this does not approach thecapabilities of light-amplified video equipment, it ismuch less expensive, and may improve image clarityenough to yield success from a bad surveillancesituation.

Unfortunately, while manufacturers are willing to touttheir light rating, they are reluctant to provideinformation on the quality of the video images atthose light levels. Minimum levels of illumination arerarely given in the context of a resolution figure orSNR. Each manufacturer uses its own subjectivemethod for determining the least amount of lightrequired for producing an acceptable image. Whatthen can the prospective purchaser use to predictperformance at minimum light specifications?

Table 9. Typical Light Levels Based on Outdoorand Indoor Conditions

Condition Typical LightLevel in Lux

Overcast night sky* 0.0007

Clear night sky* 0.002

Quarter moon* 0.01

Full moon* 0.1

Twilight* 4.0

Sunrise/sunset* 500.0

Heavily overcast* 7,000.0

Unobscured sunlight* 100,000.0

Office (florescent lights &no windows)

320.0

Office (florescent lights &windows)

430.0

Office building hallway(well lit)

54.0

Narrow hallway (dimly lit) 10.8

180 square foot room withone 150 Watt lamp on

16.1

*Reference for Outdoor levels: Light Intensity Conversion Chart, XYBION Electronic Systems, not dated.

Presently, the measurement of signal-to-noise ratio orresolution at the lighting threshold is really the onlyway that a user can judge the potential quality of avideo picture at that level. Another valid method,recently standardized, is based on the way humanssee. This method is to record video from a deviceunder test, digitize the images, and use computers toextract the same type of information the human eyeand brain do, such as edge information, noise content,frequency content (another measure of resolution),and many other parameters. These parameters, whenused in conjunction with data accumulated from manysimilar tests on many human subjects, allow thecomputer to judge the quality of an image producedby a video device in the same way a human viewerwould. These techniques were developed in thelaboratories of the Institute for Telecommunication


36

Sciences and are published in American NationalStandard T1.801.03-1996, “Digital Transport of One-Way Video Signals – Parameters for ObjectivePerformance Assessment.”

Furthermore, standardized measures for specifyingminimum illumination will soon be available. Thesewill help users ascertain quickly whether there isenough light present in some cases to even bothervideotaping. Since many settings requiringsurveillance by law enforcement and correctionsofficers will be dimly lit, these new measures will beparticularly helpful.

4.2.4 Shooting Below the Light Threshold

At some point, a situation might arise for which theproper equipment is not available. Most likely, thiswill be a situation where surveillance must beconducted in a lower light environment than wasoriginally anticipated. It may be that the availableequipment does not provide a satisfactory imageunder the required lighting situation. If such asituation arises, continue to tape because usefulinformation may be extracted using digital imagingtechniques. An example of these techniques is shownin Figure 12.

Figure 12 contains two images. The image on the leftwas obtained directly from videotape. The tape wasrecorded in a low-light situation in the laboratory,with the camera pointing at a head–and–shoulderstype picture. The ambient light level was 0.5 lux, andthe manufacturer rated the camera at 4.0 lux. Thusthe experiment was carried out at one-eighth of theminimum light level for the camera. It is obvious thatno useful identification can be made directly from theimage. The image on the right, however, is useful foridentification. How do you get from one to the other?

The image on the right is composed of individualimages that have been averaged together to reducenoise and increase the signal level. Thirty consecutiveframes (1 second worth) of video were used tocompute the averaged image. Since the noise israndom, it tended to cancel itself out over the 30frames, leaving a reasonable image. There are two

conditions that must be met for this technique towork. The first has already been mentioned: the noisemust be random, as is typically the case when lightlevels drop. Second, there must some signal there torecover (i.e., a recording in total darkness just will notwork). Finally, there must be some mechanism forcompensating for any motion that the subject hadwithin the frame during the interval being averaged.This ensures that the image of the subject lines upperfectly when the frames are averaged, making for aclearer picture.

The averaging can be accomplished in several ways.First, it is important to get the images into a computerto be processed. In this case a Sony digital camcorder(model DCR VX-1000) was used with a Canon VideoDK-1 Video Capture Kit. Once imported, theaveraging can be done with a number of softwarepackages, including high-powered computationalpackages like Matlab® and IDL®, or graphics artpackages like Adobe® Photoshop®. More detail on theprocess is given in Appendix B.

4.2.5 Color Accuracy

Color is another way to judge quality. Even whenillumination is sufficient to allow a camera to operate,there may still be built-in errors in the camera’s colorgeneration circuits that sometimes make its colorsappear less than true. Specifically, problems arisewith the phase and amplitude of the color part of thevideo signal. The phase of the color signal representsthe hue of a color, and the amplitude carries thesaturation information. Hue is defined as theparticular shade or tint of a given color, but also hascolor as a synonym.

Examples of hues that may be used in everydayconversation are red, greenish, and blue-green.Saturation refers to the amount of pure white mixed inwith a given hue. A hue that has no white mixed in issaid to be 100 percent saturated, while a hue that ishalf white is 50 percent saturated. For example, redand pink are the same hue, but red is 100 percentsaturated and pink is more like 50 percent to75 percent saturated; pink is just red with some whitemixed in. Along with brightness, hue and saturation


37

Figure 12. Extracting useful data from videotape shot in conditions below the light threshold

completely define all colors available within theconstraints of the video system. To test the coloraccuracy of a piece of video equipment, its output isplugged into a device (vectorscope) that can isolatethe color information (hue and saturation) from thebrightness (luminance) information. The hue andsaturation are then displayed and inspected separately.Color accuracy readings are given in degrees andreflect the deviation of the observed color from the“standard” color. The lower the deviation figure, thebetter. Cameras with excellent color accuracy mayhave accuracy numbers for colors within 5°.

It would be an impossible and unnecessary task tocheck all possible colors and combinations of colors;fortunately, it is sufficient just to check red, green,blue, cyan (blue+green), magenta (red+blue), andyellow (green+red). Because of this, a standard chartis available that contains just these colors – called the

“color bars” chart. Sometimes color bars arebroadcast by a TV station after they go “off the air”for the night. If a camera is aimed at a color bar chart(under appropriate illumination), then its output signalwill be ideal for testing with a vectorscope, and it canbe determined whether the camera's reproduction ofblue, for example, is accurate enough for its intendedapplication.

The reason for investigating the color accuracy of acamera or camcorder is to ensure that colorsaccurately divulge the race, hair and eye color,clothing, and other distinguishing characteristics of asuspect or other interviewee. It is also essential tomaintain color information about pieces of evidencesuch as paint chips or blood and to identify quicklyand accurately health problem symptoms, such ascyanosis, in a victim.


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4.2.6 Maximum Lens Aperture

This characteristic of cameras and camcorders tellssomething about how good the lens is. The better alens is, the faster it gathers light for conversion intoelectrical signals and the easier it is for the rest of thecamera or camcorder to maintain a noise-free image,since there is more light coming from the scene thanthere would have been with a slower lens. If most ofthe perceived applications involve nighttime ortwilight conditions, it is important to obtain the fastestlens available (within the established budget).

Most cameras/camcorders have the maximumaperture marked on (or near) the lens as an“f-number.” It may be shown, for example, as “f/1.4,”“1:1.4,” or simply “1.4.” Speed in a lens, asdetermined by the aperture, provides an indicator ofhow long it takes to expose the video pick up (or anytype of film). With an f/1.4 lens, the light can be one-eighth as bright as with an f/4 and still allow the samelength exposure. For the same brightness of light onthe subject, the shutter speed can be shortened by afactor of eight. For the police photographer, lensspeed is of the greatest value in a covert surveillancesituation where there is little natural light andsupplementary illumination cannot be used. A lowerf-number may be the difference between getting apicture and not getting it.

Table 10 lists standard f-numbers and compares therelative brightness requirements of each. The tableuses f/1.4 as a typical “best” limit for lenses, however,some cameras offer an f/1.2 lens. An f-number of 1.0is the theoretical lower limit for standard lenses.

Table 10. f-Numbers and Light Brightness

f-number 1.4 2.0 2.8 4.0 5.6 8.0 11 16 22

Relative BrightnessRequired

1 2 4 8 16 32 64 128 256

For most surveillance cameras, it is fairly easy tocover applications involving different lightingconditions by buying more than one lens. Lenses canbe switched on and off the camera body, even in the

field. Camcorders are not so flexible. The lens thatcomes with the camcorder cannot normally beremoved.7 If two camcorders are essentially the sameexcept for the maximum aperture, it may be prudentto choose the one with the lower f-number, especiallyif both show the same lux specification.

4.2.7 Minimum Focusing Distance

Almost all of today's common camera and camcorderlenses focus as close as 2 1/2 feet to 3 feet. This issuitable for satisfying most needs of law enforcementand corrections, except for acquiring some forensicfootage. If there is a need to record extremely closefootage of an object that will serve as evidence, the‘macro’ function of the lens should be engaged, ifavailable. This effectively switches the lens intoanother mode that has a focusing range from about2 1/2 feet right down to zero – which is right at thelens. In this mode, focusing is typically accomplishedwith the zoom controls and with more difficulty.

4.2.8 Zoom

Although such a function is considered a “special”lens on a photographic camera, it is the norm forvideo cameras and camcorders. Usually a lens willcome with the unit and be designated, for example, an"8:1" zoom. This means that if the lens is zoomed toits wide-angle limit (that which makes the subjectlook the farthest away), then zoomed to the other end(as close as possible), the subject will appear eighttimes as close. This extreme is called “telephoto.”While not true for all lenses, in most camcorders,zooming to the telephoto end of the lens also reducesthe light transmission (i.e., f-rating) through the lens.In spite of this restriction, having a zoom featuremeans the camera or camcorder can be used in a widerrange of situations than would otherwise be the case.

7 It is true that “wide angle” and “telephoto” lenses can bemounted in front of the camcorder’s permanently mountedlens, increasing the range of situations in which the device canbe used. These lenses do, however, generally reduce theamount of light reaching the lens by one or two f-stops.


39

When zoom functionality is solely dependent on thelens, it is considered an optical zoom. Some of thenew digital camcorders have a digital zoom feature inaddition to the optical zoom, in which they use asubset of the elements of the CCD video pick-updevice and enlarge that subset to cover the full screen.When reporting zoom ranges, manufacturers typicallymultiply the optical zoom and the digital zoomfeatures. For example, a camcorder with a 12x opticalzoom lens and a 5x digital zoom feature would betouted as a 60x zoom. That is, the image of an objectfully zoomed in (magnified) will appear 60 timeslarger than if the camera were fully zoomed out.Remember, however, that much of the increase wasdue to sampling a subset of the CCD, thus reducingthe overall resolution of the image.

4.2.9 Autofocus

A number of consumer-grade cameras and camcorderson the market offer the user the choice of eithermanually focusing on a subject or allowing the videodevice to automatically focus. In some cases, the userhas no choice – the equipment comes with only amanual or auto-focus lens. Whether the auto-focus isoptional or mandatory, it is important to realize whatits capabilities (and limitations) are before making aselection.

Two methods are typically used in auto-focus camerasand camcorders – contrast-maximization and infra-redranging. These methods are described below.

Contrast Maximization (CM)

Imagine, as in the discussion on resolution, a series ofvertical lines alternating between pure black and purewhite. If this scene is viewed with a lens system thatis in focus, the boundaries between the two types ofregions will be distinct. If the eye scans from left toright, it sees light levels alternating in sequencebetween a very low light level (a black region) and avery high light level (a white region). If the lens iscompletely out of focus, all that will be seen is a largearea of uniform medium gray (a medium light level).In fact, for any given scene, the lens setting that is in

focus also produces the maximum contrast in lightlevels. Cameras scan pictures as described above butsee pictures in terms of electrical levels. A cameracan find the best focus by changing the lens until thedifference between the highest voltage and the lowestvoltage in a scene is maximized. This principle hasbeen exploited to allow camcorders to find the “best”focus automatically and is called “contrast maximi-zation.”

Infrared Ranging (IR)

In this radar-like system, an infrared emitter, typicallylocated next to the camcorder’s lens, transmits a pulseof light that is not in the range visible to humans. Aninfrared light sensor then waits for a reflection of theoriginal pulse and notes how long it took for thereflection to return. Knowing how fast the pulsetravels, the system then calculates the distance to theobject that reflected the light pulse and adjusts thelens apparatus accordingly. These calculations andadjustments are done from 5 to 10 times per second.

In implementing both the CM and IR methods,engineers had to answer many questions. Forexample, in the case of the CM camcorder, the truefocus could be anywhere in the range of the lens (ortoo close). While sweeping from nearest to farthest,the contrast might not simply increase until focus isattained, but instead, it may increase a little, thendecrease, and then increase a lot. How should thecamcorder decide whether to find an even greatercontrast, or to stand pat on its current decision? If itstays where it is, it might not be in focus, and then juststay there, out of focus, forever. If it is in focus butgoes hunting for a better focus, it might simply wastetime, losing valuable information by recording out offocus until it comes back or stays elsewhereincorrectly.

In the case of the IR focusing camcorder, the pulseshould spread as it travels outward, away from thecamera and toward the subject to be videotaped. If itdoes not spread but stays thin as a pencil, it couldfocus, for example, through to the other side of librarybookshelves (when there is an opening through andthings and people on the other side can be seen) when


40

the books are the intended subject. If the beam is toowide, the camera could focus on the books, when it isthe people on the other side who should be monitored.In another scenario, what if the user of the camcorderis by a chain-link fence, and something else is on theother side? Should the point of focus be the chain-link fence or the object on the other side? Both casesare possible, but how does the user inform the camerawhat’s on his/her mind? He/she does not with autofocus! Manufacturers made decisions for the user.

Regardless of how the manufacturers ultimatelydecided, it is imperative that the user understand whatthey decided to do and how that impacts theeffectiveness of auto-focus for certain videoapplications. Some of the advantages and disad-vantages of the two technologies are given below:

IR focuses on glass, whether you want to or not. Thismakes observation of people in houses and vehiclesvery difficult.

CM looks for the greatest difference between blackand white. If the room is relatively dark, it takeslonger to decide that a given lens setting is right orwrong. It could take up to 30 s to focus in a well-litindoor room when the subject is of low contrastalready.

IR systems can focus perfectly on a subject even ifthere is absolutely no visible light. This does notmean the camera can operate and/or record images inpitch black surroundings. This means the camera canbe focused and ready to go, and once the light levelreaches the minimum illumination the camerarequires, it will operate. An IR autofocus camera,then, could be placed in a dark room and recordhappenings when a lamp was turned on or somesunlight shone in. From bright light to little light, the

IR focusing ability is not progressively diminished asthe light grows dimmer.

CM uses only the center third of the frame whencalculating focus; therefore the zoom interacts withthe auto-focus. CM maintains focus when movingfrom wide-angle to telephoto but loses it badly in theother direction.

Regardless of whether the auto-focus mechanism isCM or IR, depending on the particular camera, theauto-focus can be swift or slow. The swift ones tendto hunt indecisively once they get close to focus,whereas the slow ones take longer to get there but arevery accurate and stable once they decide they arefocused.

Linked in with all of this is the auto-iris, the part ofthe camera that adjusts for changing light levels. Asthe iris opens and closes, the depth of field willchange, making parts of the scene that are not at thesame distance as the subject go in and out of focus.While the CM types will be affected by this, the IRtypes do not appear to be.

4.2.10 Shutter Speed Control

The fact that most video devices in the United Statesproduce frames at the rate of 30 per second means thatif a subject moves considerably in 1/30 second, it willappear blurred under normal circumstances. One ofthe features available (with the proper device) that cansolve this problem is shutter speed control. Just aswith a photographic camera, higher shutter speedsreduce the amount of time the shutter is open anddecrease the blur seen during that time. The paybackis the faster the shutter speed, the more light that mustbe available; however, with a subject illuminated byfull sunlight, shutter speeds of one 0.0001 second arepossible with uncompromised quality.

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5. The Ergonomic Aspects of Equipment

One of the experiences people have had with newvideo equipment is they could not get it to work. No,this is not another story relating to poor workmanship,missing parts, or bad information from the salesman!In the vast majority of cases, there was nothing wrong(theoretically) with the equipment. Problems arosebecause users did not know what to do; the equipmentwas not straightforward to operate; technical manualswere incomplete, misleading, or confusing; or theequipment controls could not physically be moved orpositioned. These were all ergonomic problems.(Ergonomics is the science concerned with thecharacteristics of people that need to be considered indesigning and arranging things. That is, how shouldsomething be made so that people will interact with iteffectively?) A video product can have the bestspecifications and features in the world, but if no onecan easily use it, it has no real practical value.

This section addresses a few of the “nitty-gritty” itemsthat may be forgotten during the selection process forvideo surveillance equipment. If specifications,features, and cost all fall out as about equal, one ofthese items may be the deciding factor. Even if thevideo units mentioned below did not have anydrawbacks in specific categories, it still would beprudent to look at those kinds of categories whenactually contemplating a purchase.

5.1 Time Needed to Learn Basic and AdvancedOperations

With a technical manual as a guide, it only took about5 or 10 min for ordinary people (non-experts) to getthe various video units described in this guideworking. (That is, if the batteries came already fullycharged with the camcorders). The Sony DXC-M7camera took somewhat longer because it is a morecomplex piece of equipment (e.g., more functionswitches, feature controls, and connectors). Anofficer who had never used a camera or camcorderbefore would be ineffective if forced to use one “cold”

in a pressure situation, but 2 h of use over a couple ofdays probably would allow that officer to use all ofthe basic features adequately and to record valuableinformation. To learn and use advanced features,such as toggling sensitivity gain and autofocus,adjusting white balance, connecting a 10 W lamp tothe camcorder, and using the macro feature of thelens, some weeks of use would be required. Inaddition, there are some things an artist can do withskillful control of the camcorder that your averageoperator will never be able to do. This personalelement is no more of a problem with certain officersthan trying to photograph evidence with a standard35 mm single lens reflex camera, however.

5.2 Controls – What Kinds are Better?

This subject is general to cameras, camcorders,televisions, monitors, and VCRs. Even in this realm,things have changed a lot since the days when TVswere powered on with a loud mechanical click. Thisis mostly due to solid state electronics, but also tomaterials science. Since silicon switches use so littleenergy, it is not uncommon now for a part of anelectronic instrument to remain on even when it hasbeen turned off. Turning it back on consists ofmoving a switch that closes an electrical contact thattells the part of the instrument that remains on to turnon the rest of the instrument. Since the switch is justa contact, it can be made quite small. Unfortunately,some manufacturers have gotten overzealous in theirdesire to show off just how small they can make theirswitches, and the result is full-size camcorders thathave switches that are too small to use comfortablywith just fingers, not to mention gloves.

The most common types of controls are buttons,sliders, knobs, and switches. (See figs. 3, 9, 10, and11.) Switches are generally of the variety that can bein one of two positions and stay there. More popularthan switches are buttons, knobs, and sliders. Buttonsmost often are just electrical contacts that


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electronically toggle functions: the first time you pressit the auto-focus turns off; the next time it turns backon. Of course, if these toggle buttons are too large, itbecomes possible to bump them when it is notdesirable to do so. It could be disastrous if such abutton controlled the power for the entire camcorderor for the cassette eject mechanism. These functionsare usually protected by a slider, the function of whichis invoked by moving a spring-loaded control to theside momentarily for electrical contact. Sliders returnthemselves to a home position upon release. Sincepressure straight upon their surfaces does not bringthem to operation, they are safe for the moreimportant functions. Knobs are most commonly usedto allow the user to select one of many options. Oneexample of this is the power-on knob of the SonyDCR VX-1000. This knob allows selection of VCRor camcorder mode, as well as various levels ofautomation.

An example of a more complicated control that can befound on some devices is the power control on theSony CCD-V99 camcorder. It has a center positionand slides to one side to use the device as a camcorderor to the other side to use it as a VCR. Before movingit from its center position, however, a tiny greenbutton in the middle of the sliding switch must bedepressed to unlock it. It has proven to be aformidable task even with bare fingers.

Even simple controls like buttons can be madedifficult to operate by placement. Many timesfrequently used controls are placed behind covers ordoors. This slows access to those controls. Oneextreme example of poor placement are the menucontrols on the Sony DCR VX-1000. These controlsare behind the battery compartment door, on the sideclosest to the hinge. This makes the buttons awkwardto reach without the added complication of having tohold the camcorder at eye level to see the menu in theviewfinder and having the battery door continuallybumping into your chin.

Monitors and televisions are used almost exclusivelyindoors or at least not in sub-zero outdoor weather.Since they are relatively large, there does not seem tobe a leaning by designers to give them unnaturally

small switches. Operation is rarely an ergonomicsproblem.

In general, understand that modern equipment willhave many controls to maximize functionality, andthey may need to be somewhat small to fit them alllogically onto a control panel. Beware of controls thatare smaller than they need to be – especially if youmay need to use the equipment with gloves or in tightplaces.

5.3 Camcorder Use with Gloves and Other Heavy Clothing

Most of the hand straps that come manufactured withcamcorders can be adjusted to fit large hands, evenones sporting gloves that are not too thick (e.g.,driving gloves or work gloves). Shoulder supportedcamcorders (most standard size VHS units) andcameras may not have a hand strap but an area builtthrough the device that is intended for use as a grip.The size of this grip may not be adjustable, and thisshould be taken into account when consideringpurchase. The low end of the operating temperaturerange is usually specified to be above the freezingpoint of water (32 °F)anyway, and extremely thickand heavy gloves probably would not be needed atthis temperature. The other consideration when usingthick, heavy gloves is the size of the buttons andknobs on the unit. This should not be a problemeither if gloves are not too thick, given the typicalbutton and knob size.

5.4 Weight and Handling Versus Steadiness When Operating

Weight is mostly irrelevant when dealing with devicesintended to sit on a shelf, such as most VCRs andmonitors. Some monitors can be transported betweensites, but system design options should not includehaving a monitor strapped to a human assistant. Forcameras, portability, weight, and handling are asignificant issue, because manufacturers always try tocompromise between quality, manufacturing cost, andconsumers’ desires for something small and easy tooperate. This is even more true when you try todesign a tape recorder into the same small enclosure

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as the camera. Such a device is called a camcorder.As far as weight goes, it is desirable to keep it low,but stability will suffer if weight is insufficient to keepthe camcorder steady when the operator moves.Muscles sometimes shake a little when asked toremain perfectly still. At the other end of the extreme,even aside from the obvious discomfort of carryingaround a camcorder weighing 15 lb, excessive weightcan make muscles shake just from the sheer effort ofsupporting it after awhile. Somewhere in between isthe ideal weight for a particular operator.

In addition, since 8 mm videotape is so much smallerthan VHS videotape, most camcorders employing itare smaller and lighter than their VHS counterparts.They are carried in front of the operator’s body andface, whereas VHS models are typically carried on theshoulder, as simple video cameras are. The compactversion of VHS, called VHS-C, can be carried in frontof the operator like 8 mm camcorders also, since theirvideotapes are much smaller than standard VHSvideotapes. If the camcorder is carried in front of theoperator, the device is typically lighter than onecarried on the shoulder, but it has only the operator’stwo hands to support and steady it. If the camcorderis carried on the shoulder, the device is typicallyheavier than the 8 mm or VHS-C varieties, but theshoulder support is both quite strong and very stableor steady.

All cameras and camcorders come with a screwmount on the bottom for attaching to a tripod. Atripod can serve to simplify surveillance, as theburden of supporting the machine is moved to thetripod, and there is no risk of a human operatorwavering off target.

5.5 Equipment Compatibility

If your entire contingent of video equipment is ofVHS format and you acquire one 8 mm camcorder,then when you want to view the tapes you haverecorded with the 8 mm camcorder, you will have touse the camcorder for playback. In addition, withinthe VHS universe, if you acquire a VHS-C camcorder,you will need an adapter to play its tapes on standard

VHS systems. These adapters are usually includedwith VHS-C systems.

5.6 Helpful and Useless Features

The ability to switch off automatic features isinvaluable if an operator is skilled in the use of aparticular piece of video equipment. There is alwaysa situation where autofocus is undesirable or ill-suitedor the operator must force the iris open to gain detailfor the features of a face against a brighterbackground.

Since camcorders are already quite a mature product,most of the features that are required to obtain qualityimages are available on almost every model.Manufacturers try to distinguish their productsthrough the addition of features that can be generallyconsidered useless for video surveillance applications.Part of the reason for this is in most cases it costs themanufacturer so little to include features (e.g., titling,strobe effects, artful fades or dissolves from one taketo another) that they are just installed as a matter ofcourse. This is especially true as microprocessorsevolve and drop in price. It is conceivable that, sincethe complexity of the device is increased toincorporate these features, the chance is increased thatan officer not so experienced with video equipmentmight press the wrong button and actually lose theability to accurately record information.

5.7 Viewfinders

Are some viewfinders bigger and better than others?Until recently, viewfinders were almost always just asmall (about 1 in diagonal) monochrome CRTconnected electrically to the body of thecamera/camcorder. More recently, color LCDviewfinders are coming to dominate the camera andcamcorder market. These viewfinders are typicallymounted within an enclosure that can swivel up andaway from the body to allow the user to get thecamera lower for shots of children or to shoot undera fence, for example. The viewfinder is madecomfortable to place against the user’s face byincluding an eyecup of very flexible rubber molded toapproximate the average user's facial contours. Since


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the user is actually placing his eye up to the eyecupwithin 1 in or 2 in of the CRT within the viewfinderand the eye can’t focus at that distance, a lens isprovided within the viewfinder between the eye andthe CRT. This lens can be adjusted to match thenatural focal length of the user’s eye so that extendeduse of the viewfinder is comfortable.

In addition to viewfinders, many consumer camcor-ders are available with a 2-in to 4-in LCD monitorthat flips out from the camera body to tilt and swivel.Many camcorders with an LCD monitor also have aviewfinder, although some models have totallyreplaced the viewfinder with the monitor.

It is not a straightforward choice to select between thetypes of viewfinders. The small viewfinder must beheld to the eye but the required stance is stable, andthe aiming motion is quite natural, ensuring theintended subject gets recorded on the tape. The LCDmonitor allows more flexibility in holding the cameraand a larger display on which to read all theinformation provided by the camcorder. It also allowsthe videographer to interact more directly with thosearound, making the subjects more comfortable withthe presence of the camera. Sacrificed are a little bitof stability and precision. If possible, a camcorderwith both would be desirable and provide the mostflexibility.

5.8 Battery Life and Replacement

Rechargeable batteries8 supplied by the camcordermanufacturer are intended to last for 2 h – the lengthof time available for recording on one videotape(8 mm and VHS). When one tape is completely fullof recorded material, tapes and batteries can beswapped simultaneously, and then the expendedbattery can be connected to the recharging unit so itcan be ready in 2 h. Multiple batteries are rarelysupplied with the camcorder, so it will be necessary tospecify extra batteries at the time of purchase of the

camcorder. Even though extra batteries are notincluded, some units provide charging capacity fortwo other batteries while another is being used.

Some of the more compact camcorders carry theirrechargeable batteries in a compartment under thehand strap. Thus, during camcorder operation, theuser’s hand wraps around the battery compartment.This can be a good attribute, because the warmth thatthe hand provides also keeps the battery warm and,electrically, more potent. This can also be bad,because it can be less than convenient to try toexchange batteries in a hurry when a panel has to beremoved and batteries have to be removed out fromunder the hand strap.

5.9 Tapes – Cost versus Quality; Problems Read-ing Tapes

It is commonly felt (and consumer product testingfirms have found) that tape is tape is tape, and alltapes record the full bandwidth of their respectiveformats (e.g., VHS, 8 mm, S-VHS). There does notseem to be a difference even between regular gradeand “high-grade” tapes. Also, there is no good reasonto pay extra for tapes designated as “hi-fi,” since anytape can record high-quality sound in a VCR thatrecords in the VHS hi-fi format.

The defect that is found on videotapes manifests itselfas “dropout,” where the signal is lost temporarily, sothe playing machinery must resynchronize. It is thefrequency of these dropouts that determines therelative quality of videotapes. It is worth noting thatthe average viewer does not notice most dropouts,although this is little consolation to work as critical aslaw enforcement and corrections. As a general rule,it may be a better approach to buy brand-name tapeson sale than to buy off-brand tapes that may not havesatisfied the same types of quality manufacturingstandards.

As far as reading tapes, there should not be anyproblems except for those associated with theenvironment. The heads that read the tape are actuallydipoles mounted in the surface of the rotor, and thehelical rotor actually does not touch the tape being

8 For more information on batteries, consult the “NewTechnology Batteries Guide,” NIJ Guide 200-98. This andother NIJ guides are available from NIST/OLES, 100 BureauDr., Stop 8102, Gaithersburg, Maryland, 20899-8102.

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transported across it at an angle but forces a film of airbetween its own surface and the tape because offriction and high rotation speeds. Moisture particlesin the atmosphere (from simple humidity or outrightrain) can be larger than the gap between the rotor andthe tape, causing drag and improper operation. Thiscan be sensed and relayed to the operator, usually witha "DEW" indicator, such as an LED. When thisindicator appears, remove the battery and let thecamera sit (with all doors open) in a dry spot for acouple of hours (or overnight) before trying to use itagain. This should give the moisture enough time toevaporate.

5.10 Maintenance for a Machine with Tape Heads?

While some newer camcorders and VCRs have selfcleaning heads, head cleaning is one of the mostcommon maintenance tasks for these devices. Here isa paragraph from one manufacturer’s operatinginstructions:

Cleaning the Heads: It is recommended thathead cleaning be performed by a qualifiedservice technician. Please contact yournearest Service Center. An alternate solutionis to obtain a head–cleaning cassette. Thereare many types of cleaning cassettes, so besure to follow the cleaning instructionscarefully. Excessive use of the cleaningcassette could shorten head life. Use thiscassette only when a head clogging symptomoccurs.

Cleaning heads on any helical scan device, whetherVCR or camcorder, is almost a judgement call. They

do not need to be cleaned exceedingly often unless thework they record or reproduce is critical. Whencleaning is necessary, it can best be done bydisassembling or reaching in with special equipment– in other words: professionally. It can be done withhead cleaning tapes, which consist of an abrasivematerial manufactured into a cassette just like astandard videotape. They are first wet with a headcleaning fluid and then “played” in the camcorder orVCR. Sometimes, because of their abrasiveness, theyare not recommended by the manufacturer of thecamcorder or VCR, and sometimes they just do not dothe job very well anyway.

5.11 Documentation/Instructions

Camcorders are manufactured exclusively in foreignlands. Unfortunately, manufacturers believe, for somereason, it is not necessary to hire native speakers fromtarget market countries to write or assist in the writingof documentation for these pieces of equipment. Theresult can sometimes be confusing and frustrating.

Documentation has been found to be complete. Thetechnical writers working for the manufacturer try tomake documentation complete for a unit by bindingtogether manuals for several closely related units.This is not enough, however, since the writing is oftenpoor in grammar and clarity. If a camcorder doesNOT have a particular feature, such as the capabilityof turning off autofocus, it probably will not say so inthe manual. The obvious intent is not to highlight alack of something in the product, but it might bebeneficial to the user to know it as soon as possible.


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6. Summary

With all the advances in videography today, there willcome a day in the not-too-distant future when stillphotography will no longer be the preferred techniquefor recording data for most law enforcement andcorrections needs. As the resolution and electronicshutter speeds of video equipment continue toimprove and the costs of video units are reduced evenfurther, the current advantages of conventionalphotography will diminish. Also, digital video andmultimedia computing could have a significant impacton the future of video surveillance and how the dataare gathered and processed. That is why the basicconcepts of this guide are important to both imminentpurchasing decisions and planning in anticipation ofnew technologies.

This guide has attempted to convey the many aspectsof video in enough detail to allow a fundamentalunderstanding of technical parameters and how theyrelate to law enforcement needs. It is hoped, however,that the discussions of the guide will have stimulatedreaders to conduct subsequent investigations into theever-changing capabilities and applications of videogear. Only by having a clear recognition of what thepotential benefits are, can those in the lawenforcement and corrections communities hope totake advantage of the ongoing video revolution.


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7. Glossary

amplified light – An attribute of a camera or othervideo device indicating use of a special module toamplify ambient light before it gets to the pick upunit.

amplitude – The voltage level of a signal. Could berelative (e.g., peak-to-peak for ac signals) orabsolute (for dc signals).

aspect ratio – In facsimile or television, the ratio ofthe width to the height of a picture, document, orscanning field. NTSC television has standardizedthe aspect ratio at 4:3 (i.e., the picture is widerthan it is high by a factor of 1 1/3). If an image isnot reproduced at the intended aspect ratio,objects in the image are distorted.

automatic iris control – An automatic control thatregulates the amount of light that reaches thevideo pickup unit.

auxiliary jacks – Any of a number of connectors thata piece of video equipment can have to allow it tobe connected to and interwork with otherequipment.

bandwidth – The difference between the limitingfrequencies within which performance of a device,in respect to some characteristic, falls withinspecified limits. An analogy to bandwidth mightbe the width of a street or a highway, where eachlane is a radio frequency.

battery – A device used for storing energy until it isrequired for use by a piece of equipment. Enablesequipment to work without being plugged into awall outlet.

battery memory – In rechargeable batteries, refers tothe tendency of some batteries to “remember” thelevel to which they were charged or discharged,

reducing the overall useful storage capacity of thebattery. (See NIJ Guide 200-98, “NewTechnology Batteries Guide,” for moreinformation.)

black balance – See white balance.

blue-only control – A switch that turns off the red andgreen electron guns in a monitor. This allows forthe monitor to be calibrated based on the signalfrom the blue gun only.

book mark – A feature of camcorders and recordersthat allows the user to quickly find the end ofpreviously recorded material so that additionalrecording can resume from that point.

brightness – A qualitative attribute of visualperception in which a source appears to emit agiven amount of light. In monitors, overallbrightness is dependent on the high-voltage leveland the dc-grid bias.

broadcast quality – A generic descriptor indicating apiece of equipment is of sufficient quality to beused regularly by the broadcast televisionindustry. Typically, the requirement is thatresolution be greater than 450 TVL.

CCD (charge coupled device) – These tinylight-to-electric-charge transducers are placed inrectangular arrays on silicon wafers and used asvideo pickup devices instead of electron tubes.The signal is read out from the array sequentiallyfrom side-to-side and top-to-bottom to determineone video frame.

chrominance – In color television, that signal orportion of the composite signal that bears thecolor information.


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clarity – A qualitative term generally referring to thecombination of resolution, contrast, and coloraccuracy.

CM (contrast maximization) – a technique forautofocusing cameras and camcorders based onmaximizing the contrast of the video signal.

color – Having a non-white spectral characteristic.

comb filter – a filter which helps to minimize the lossof resolution and reduce streaking and wavy edgeson fine patterns. Common in middle range tohigh-end television displays and monitors.

contrast – In display systems, the relation between (a)the intensity of color, brightness, or shading of anarea occupied by display elements, a displaygroup, or a display image on the display surface ofa display device and (b) the intensity of an areanot occupied by a display element, a displaygroup, or a display image. For a monitor, contrastis determined by the peak-to-peak amplitude ofthe video signal.

counter – In cameras and recorders, counters are usedto keep track of tape position between start andfinish. Counters can be in arbitrary units, timecounting up, or time counting down.

CRT (cathode ray tube) – the vacuum (electron) tubethat generates an image in a television monitorusing cathode-ray electrons.

dB (deciBels) – 1) one tenth of the common logarithmof the ratio of relative powers (P), equal to 0.1 bel.The formula is given by dB = 10 log10 (P1/P2).2) One-twentieth of the common logarithm of theratio of relative voltages (V) or currents (I), equalto 0.1 bel. The formula is given bydB = 20 log10 (V1/V2) for voltage anddB = 20 log10 (I1/I2) for current.

dichroic lens – A lens in a camera which splits theincoming light into the three primary colors (red,green, and blue) so they can be picked up byseparate CCDs or different areas on one CCD.

digital zoom – A relatively new feature of digitalcameras whereby they use only a portion of thepickup device and magnify the image to fill thefull frame.

distance – The position of the subject relative to thecamera.

DSO (digital storage oscilloscope) – an electronic testinstrument used primarily for making visible theinstantaneous value of one or more rapidlyvarying electrical quantities as a function of timeor of another electrical or mechanical quantity. Itsstorage function allows several values to berecorded (and displayed together).

DV in/out – IEEE 1394 (also known as “FireWire”)interface available on digital camcorders.

dynamic contrast control – An automatic control tomaximize the contrast of a scene. Generally, useof dynamic contrast control produces animprovement in overall picture quality.

electron beam spot size – The diameter of the focusedelectron beam that causes the phosphor on amonitor screen to fluoresce.

edit controller – A jack on a piece of equipment thatallows it to be precisely controlled by anotherdevice for the purpose of editing tapes.

electron tube – A vacuum tube designed to focus anddirect beams of electrons. A common type ofelectron tube is a television picture tube (i.e., aCRT).

electronic shutter – Use of electronics to simulateplacing a shutter in front of a video pick-updevice.

environmentally robust – A manufacturer’s subjectiveclaim that their equipment can operate in a varietyof temperature, humidity, lighting and physicallyabusive conditions.

Glossary

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fade – A non-abrupt interruption of the signal. Invideo, generally refers to a graceful transitionfrom one video signal to another.

filters – In electronics, a device that transmits onlypart of the incident energy and may therebychange the spectral distribution of energy.

flying erase head – In camcorders and recorders, arecording technique that allows for a single frameto be erased from a video tape and thenimmediately replaced with a frame from anothersource. This allows for smooth transitionsbetween scenes.

focus – The mechanism used to ensure that the sceneproduces a sharp image on the video pickupdevice.

gain-up – A control to increase the gain on the outputof the video pickup device in low-light situations.

headphone jack – On video equipment, this is usuallya 1/8 in stereo phono jack.

high definition television (HDTV) – Television thathas approximately twice the horizontal and twicethe vertical emitted resolution specified by theNTSC standard.

high-speed shutter – A physical or electronic shutterthat operates at faster than 1/60 s.

hue – The visible spectral content of an image or partof an image, which depends on the phase angle ofthe chrominance signal. The phase is varied withrespect to a color synchronizing signal by a “tint”or “hue” control. This control is subjectively setfor the correct hue of any known color on thescreen (e.g., green grass or blue sky), then allother hues are automatically corrected, since thecolor synchronization holds all hues in the properphase with respect to each other.

image stabilization – A camcorder or camera featureto reduce the visible effects of shake and wobbleintroduced by hand-holding the camera. Twotechniques are currently used to accomplish this.

The first is through the use of a deformable prism.As the camera/lens detects shake and vibration,the prism is reshaped to provide stability to theimage. The second is to electronically remove theeffects of shake and distortion by modifying theoutput signal from the pick-up device.

index – A feature that “marks” the videotape eachtime recording is started, enabling the user toeasily find a particular recorded section of tape.

infrared light – The region of the electromagneticspectrum bounded by the long-wavelengthextreme of the visible spectrum (approximately0.7 µm) and the shortest microwaves(approximately 0.1 mm).

infrared playback – See wireless playback.

inputs – The types of signals that a device can receive,and the connectors through which those signalsare received.

intensifier – A device placed in front of a camera orcamcorder’s pickup device that amplifiesavailable light from a scene.

IR ranging – An autofocus technique that uses aninfrared signal to determine the optimum focusingdistance.

iris – The adjustable physical opening that lightpasses through en route to the video pickup unit.

intermediate frequency (if) – A frequency to which acarrier frequency is shifted as an intermediate stepin transmission or reception.

LANC – Sony’s edit control interface for high-endconsumer equipment.

LCD monitor – A viewing device for a camera orcamcorder that is based on liquid crystal displaytechnology and is 2 in to 4 in in size.

lens compatibility – Indicates a camera has manyinterchangeable lenses, including interchange-ability with those of other manufacturers.


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lens mount – The physical connection between thelens and the camera. The most common lensmount for video cameras is the “C” mount.

light (1) – In a strict sense, the region of theelectromagnetic spectrum that can be perceived byhuman vision, i.e. , the visible spectrum, which isapproximately the wavelength range of 0.4 µm to0.7 µm.

light (2) – An attachment for a camera or camcorderto help illuminate scenes where available light istoo low to allow recording of a satisfactory image.

low light – Low-light cameras typically havepublished minimum acceptable light levelsbetween 0.1 lux and 2 lux.

luminance – In color television, that signal or portionof the composite signal that bears the brightnessinformation.

lumen – A well-defined measure of light poweremitted by a source.

lux – The light level incident on a 1 square meter areawhen a lumen of light is distributed across it.

macro mode – A special mode for some lenses thatallows focusing at closer distances than normal toprovide greater magnification of a small object ordetail on a larger object.

microphone holder – A bracket on a camera orcamcorder that allows attachment of an externalmicrophone.

minimum illumination – The minimum ambient lightlevel (usually given in lux) required to give thecamera a sufficient signal to make an “acceptable”picture. Each manufacturer has a differentdefinition of acceptable.

monitor bridging – a mode in which a monitor canreceive and display a video signal and then pass iton to another device without modification.

motion sensor – An automatic sensor in a camera orcamcorder that allows the system to be activatedwhen motion is detected and deactivated at aspecified interval after motion ceases.

multiple heads – In video playback units, multipleheads improve the image quality during high-speed and slow-motion playback.

multiple mounting holes – For cameras, multipletripod mounting holes enable the camera to bebalanced atop the tripod to provide more stableimages.

noise – A disturbance that affects a signal and maydistort the information carried by the signal, or,loosely, any disturbance tending to interfere withthe normal operation of a device or system.

noise reduction – Using filtering or digital signalprocessing techniques to reduce the amount ofnoise in an image. Noise reduction figures of6 dB are common.

NTSC (National Television System Committee) –denotes the body that set the original standards forAmerican television and is also used as areference to the television standard theypublished.

NTSC video – The North American standard (525-lineinterlaced raster-scanned video) for thegeneration, transmission, and reception oftelevision signals. Note: In addition to NorthAmerica, the NTSC standard is used in CentralAmerica, a number of South American countries,and some Asian countries, including Japan.

optical zoom – The zoom achieved by a lens.

phase – Of a periodic, varying phenomenon (e.g., anelectrical signal or electromagnetic wave), anydistinguishable instantaneous state of thephenomenon, referred to a fixed reference oranother periodic varying phenomenon. Note: Thephase of a periodic phenomenon can also beexpressed or specified by angular measure, with

Glossary

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one period usually encompassing 360° (2 πradians).

photo mode – a camcorder/videotape recorder“captures” a single frame of video and recordsthat one frame for 6 s to 10 s on the videotape,essentially making a still photo on the videotape.

pixel – In a raster-scanned imaging system, thesmallest discrete scanning line sample that cancontain gray scale information. An abbreviationfor picture element.

playthrough – The condition of taking a known input,passing it through a device, and comparing theoutput of the device with that known input.

radio frequency (rf) tuner – The part of a circuit thatcan be adjusted to resonate at a particularfrequency. Allows “channels” to be receivedfrom broadcast or cable systems.

remote control – a device that is detached from themain chassis of a piece of equipment, yet providesa mechanism for the user to control that piece ofequipment. The two most common types ofremote control are wired and wireless. Wiredremotes require a physical connection (via wire)from the remote control to the main chassis.Wireless remotes typically use an infrared signalto communicate between the remote control andthe main chassis.

resolution – A measurement of the smallest detail thatcan be distinguished by a video system or deviceunder specific conditions.

rf (radio frequency) – any frequency within theelectromagnetic spectrum normally associatedwith radio wave propagation. Normally,information signals are modulated to betransmitted at a radio frequency.

RGB (red-green-blue) – pertaining to the use of threeseparate signals to carry the red, green, and bluecomponents, respectively, of a color video image.

RS-170A (EIA-170) – An Electronic Industries

Alliance (EIA) standard describing a black andwhite television system containing 525 lines intwo interlaced fields at a field rate of 59.94 Hz.This is the basis of the modern, North AmericanNTSC television system.

saturation – In video systems, the level of colorrelative to the maximum handling capacity forthat color. The level of saturation is dependent onthe level of the chrominance component of thevideo signal.

scan rate – The frequency at which the electron beamscans a single line of an image. This is 15.7 kHzfor an NTSC system and can be as high as100 kHz for computer monitors.

screen size – the diagonal dimension of a displayscreen (measured in inches or centimeters).Sometimes part of a display screen may be hiddenbehind a plastic housing (i.e., the case of thedisplay), thus causing a mismatch between thepublished screen size and the viewable screensize.

self timer – A feature of a camcorder or videorecorder that allows it to turn itself on and/or offat a particular time or time interval.

sensitivity – In an electronic device (e.g., acommunications system receiver such as atelevision), the minimum input signal required toproduce a specified output signal having aspecified signal-to-noise ratio or other specifiedcriteria.

shutter – A device that opens and closes, allowing ordisallowing light to reach the video pickup device.

signal – Detectable transmitted energy that can beused to carry information.

SNR – signal-to-noise ratio – the ratio of theamplitude of the desired signal to the amplitude ofnoise signals at a given point in time. Note 1:SNR is expressed as 20 times the logarithm of theamplitude ratio or 10 times the logarithm of the


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power ratio. Note 2: SNR is usually expressed indB and in terms of peak values for impulse noiseand root-mean-square values for random noise. Indefining or specifying the SNR, both the signaland noise should be characterized (e.g., peak-signal-to-peak-noise ratio), to avoid ambiguity.

speaker – An electrical signal to audio sound pressuretransducer.

special effects (special FX) – Any number of featuresadded by camera manufacturers that affect thevideo in special ways. Includes fades, wipes, andsolarization.

still video – Recording a single frame of video toseveral seconds of videotape, essentially creatinga still image that can be annotated with audio (i.e.,use the audio recording tracks to recordinformation about the picture).

S-VHS (Super VHS) – the same as standard VHSexcept that the luminance carrier is shifted to ahigher frequency, allowing for greater carrierbandwidth and, hence, greater resolution (about400 TVL).

S-VHS -C– A piece of equipment using S-VHSvideotape in a smaller cassette.

synchronization signal – a signal used to synchronizepieces of video equipment to a common clock. Inmedium- and large-sized video facilities, it isnecessary to synchronize all pieces of equipmentto avoid problems when recording or playingvideo.

TIFF (Tagged Image File Format) – a standardizedfile format used to store images.

time-lapse – The technique of recording one frame ata time at specified intervals. When played back atnormal speed, time appears compressed, allowingviewing of a whole day’s worth of video in just afew minutes.

tint – See hue.

titling – Referring to the ability to overlay text orsymbols onto a video signal. An example oftitling is credits at the beginning or end of amovie.

TVL (television lines) – a unit of horizontal resolutionfor video devices.

VCR (video cassette recorder) – denotes all formats ofvideo tape recorder except reel-to-reel.

VHS (video home system) – a piece of equipmentusing ½ in video tape and a cassetteapproximately 4 in by 7 1/2 in.

VHS -C – A piece of equipment using standard VHSvideo tape in a smaller cassette.

video – An electrical signal containing timing(synchronization), luminance (intensity), and oftenchrominance (color) information that, whendisplayed on an appropriate device, gives a visualimage or representation of the original imagesequences.

viewfinder compatibility – Implies that a camera orcamcorder has a jack to which an LCD monitorcan be attached.

white balance – A camera control that controls theoverall intensity of a video signal. Most camerascome with an automatic white balance adjustmentthat can be overridden in situations where thecontent of the scene is not “average” (i.e., thesubject is either lighter or darker than average).

wind screen – a device (typically sponge rubber) thatis used to cover a microphone and prevent windfrom striking the diaphragm and causingextraneous (usually annoying) noise while stillallowing sound waves to pass through, creating anaudio signal.

wireless playback – A feature on some camcordersand recorders that allows playback on a televisionor monitor without physically connecting wires.

Glossary

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This is accomplished through the use of aninfrared transmitter in the camcorder/recorder andan infrared receiver that needs to be attached tothe television/monitor. The receiver is usuallyincluded as a part of the package.

YIQ – Luminance, In-phase, Quadrature (the letter Yis commonly used in video work as a symbol forluminance).


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Appendix A. Information Resources on the Web

Below is a list of web addresses for companies sellingvideo equipment that might be useful in videosurveillance applications. This is not acomprehensive list. Inclusion or exclusion neitherimplies that the products of one company are better

than the products of another for a given application,nor does it imply that all claims made by thesecompanies are accurate. Before purchasing anyproduct, check as many options as possible.

http://www.advancedalarms.com

http://www.advdig.com

http://www.canon.com

http://www.cohu.com

http://www.concealedcameras.com

http://www.dxsystems.com

http://www.eagletcs.com

http://www.electrophysics.com

http://www.eyeqsys.com

http://www.jeffhall.com

http://www.jvc.com

http://www.midniteyes.com

http://www.midwestcommunications.com

http://www.p2comm.com

http://www.panasonic.com

http://www.rock2000.com

http://www.rparker.com

http://www.sharpcom.com

http://www.sharpelectronics.com

http://www.sony.com

http://www.spiderweb1.com/pi-supply

http://www.spyman.com

http://www.spyshops.com

http://www.spysite.com

http://www.spyworld.com

http://www.spyzone.com

http://www.supercircuits.com

http://www.visualmethods.com

http://www.wireless-experts.com

http://www.wirelesstech.com

http://www.xybion.com


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Appendix B: Effect of Low Light Situations onCameras

To provide more detailed information on the effects ofshooting in low-light situations, testing on actualvideo gear was conducted in a major Federal video-quality laboratory. This appendix illustrates howimage quality changes as light levels change. Inaddition, one image enhancement technique, usefulfor extracting a useable image from footage taken intoo little light, is demonstrated. This technique can beemployed by someone with moderate computer skillsworking with commercial software on a standardpersonal computer.

B.1 Working in Less-Than-Ideal Light

To illustrate the effects of using cameras in low-lightsituations, experiments were conducted to show howthe ability to distinguish human faces changes as lightdecreases. Furthermore, the experimental resultsillustrate the impact of both optical and digital zoomand differences in manufacturers’ claims of a certainlight level rating.

This test was designed and conducted in this way. Aone-eighth scale photograph of a recognizable personwas mounted in front of the camera in a controlledlighting environment. Each of the two camcorders inthe test were aimed at the picture and positioned suchthat the head and shoulders of the individual in thepicture filled the frame at each of three distances:minimum, full optical zoom, and full digital zoom.Lighting levels started at a level high enough togenerate a good quality picture and were thendecreased to approximately 2.4 lux. At that point, a0.9 neutral density filter (which blocks 90 percent ofthe light passing through) was added to the cameralens, allowing the room lights to be 10 times brighterthan what the camera actually was seeing. Using thistechnique allowed the experiment to proceed to thecamcorders seeing an effective light level of 0.1 lux.

Light readings were taken with a Tektronix J18Photometer and J1811 Illuminance Head with thesensor positioned over the face in the photograph.Once the reading was taken, the sensor was movedaside, and video of the photograph was recorded.

Table B-1 lists the camcorders used in this experimentand the relevant specifications of those devices. Onemight notice the maximum aperture varies forCamera B but not for Camera A. This is becauseCamera B uses a variable aperture zoom. Variableaperture zooms generally have a smaller maximumaperture as the lenses are zoomed to their highestmagnification. This is a disadvantage in low-lightsurveillance situations, but there are tradeoffs.Variable aperture lenses are smaller and lessexpensive to design and manufacture than fixedaperture zooms, such as the one used in Camera A.

Table B-1. Cameras used in the low-lightexperiment and their specifications

Camera A Camera BTape format Mini-DV Mini-DVOptical zoom 10x(5.9–59 mm) 14x(5.2–72.8 mm)Maximumaperture

f 1.6 f 1.8 – 3.2

Digital zoom 2x 2.5xTotal zoomrange

20x 35x

Minimumlight rating

4 lux 2.5 lux

Figures B-1 and B-2 show the facial identificationability of Camera A and Camera B (respectively) at 14different light levels. There are many things to note inthese two figures. For Camera A, the minimum lightlevel to achieve facial identification is about 0.8 lux.For Camera B, it is about 1.5 lux. This is especiallyinteresting given that Camera B has a lower minimum


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Figure B-1. Effect of diminishing light level on image integrity. Camera = Camera A. Distance = minimumdistance. Light levels (in lux, from top left): Row 1 - 19.0, 7.6, 4.3, 3.4. Row 2 - 2.2, 2.2*, 1.5*, 1.0*. Row 3 -0.8*, 0.5*, 0.35*, 0.24*. Row 4 - 0.17*, 0.10* (* indicates effective light level while using 0.9 neutral densityfilter.)

Effect of Low-Light Situations on Cameras

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Figure B-2. Effect of diminishing light level on image integrity. Camera = Camera B. Distance = minimumdistance. Light levels (in lux, from top left): Row 1 - 19.4, 7.6, 4.4, 3.3. Row 2 - 2.4, 2.5*, 1.5*, 1.0*. Row 3 -0.8*, 0.5*, 0.36*, 0.24*. Row 4 - 0.17*, 0.11* (* indicates effective light level while using 0.9 neutral densityfilter.)


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light rating. In fact, it is useful to compare imagequality of the two camcorders at their respectiveminimum light rating. Camera A provides a muchmore colorful and identifiable face at approximately4 lux than Camera B does near its rated 2.5 lux. Thisis just visual evidence of the lack of measurementstandards for camera and camcorder specifications. Inboth sets of images, one can notice “hot spots” orspots that are brighter than they should be. This isdue to reflections off the image. Because the cameralenses had such a wide field of view for generatingthese data, it was possible for them to pick up thebrightness of the lighting source reflecting off theglossy image paper. Finally, for this part of theexperiment, the lens of Camera A was about 9.5 infrom the image, while the lens of Camera B was about8.5 in distant. The required difference in placement isconsistent with the difference in the shortest focallength for the lens: 5.9 mm for Camera A and 5.2 mmfor the Camera B.

Figures B-3 and B-4 are similar to B-1 and B-2 exceptthey were taken at the maximum optical zoom levelsof Camera A and Camera B, respectively. Again, notethe minimum useable light level for Camera A isabout 0.8 lux. Camera B, however, does not producean identifiable image below 3.4 lux, a significant shiftfrom closest zoom range. This is due to the variableaperture zoom employed. The shift of minimumacceptable light from 1.5 lux to 3.4 lux mirrors thechange in maximum aperture from f 1.8 to f 3.2. Forthis part of the experiment, Camera A was positionedat 54.5 in from the subject while Camera B waspositioned at 69.5 in. Again, the difference isconsistent with the focal length of their lenses (59 mmfor Camera A and 72.8 for Camera B).

Figures B-5 and B-6 reveal the effects of using digitalzoom in addition to the optical zoom. Immediatelynoticeable is the increased speckling or grain. This isbecause the cameras only use a portion of the CCDarray to pick up the image: 50 percent for Camera A,40 percent for Camera B. Camera B showssignificantly more degradation from using the digitalzoom than Camera A does. It also requiressignificantly more light for a useable picture. The

lowest acceptable light level for identification is 31lux. For Camera A, it is still possible to identify thesubject at 4.3 lux. For this experiment, Camera A was131 in from the subject and Camera B was 175 in.

B.1.1 Enhancing the Images

There may come an occasion when it is absolutelynecessary to record video in light levels below what isknown to be acceptable for the purposes of thesurveillance. In these situations, it is best to take thehighest quality video possible (i.e., stable camera, aslittle motion in the scene as possible). Afterwards, itmay be possible to extract some useful informationfrom the tape using image processing techniques.

One of the simplest techniques involves “capturing”or recording a sequence of video frames to acomputer’s hard disk and then averaging the imagesto improve the signal-to-noise ratio. Figure B-7shows the effects of averaging 30 frames of video forCamera A at maximum optical zoom. Note it ispossible to identify the subject at a light level of 0.23lux.9 This is a significant improvement over the 0.8-lux light level that was required without averaging(fig. B-3). The procedure to accomplish this follows.

To begin, the video was taken using Camera A, adigital camcorder. The camcorder was connected toan IBM-compatible personal computer (133 MHzPentium™ running Microsoft Windows 95®) with theCanon Video DK-1 DV Capture Kit installed usingthe cable supplied with the capture kit. (This capturekit is compatible with all digital camcorders that havean IEEE 1394 “Fire Wire” interface, and has norelationship to the manufacturer of Camera A orCamera B.) Using the supplied software (DVCommander®), 30 consecutive frames were saved onthe PC’s hard drive. The frames had 640 x 480 pixelresolution and were saved as TIFF (Tagged ImageFile Format) images. The files were then individually

9 At a light level of 0.23 lux, the image in the viewfinder ofthe camcorder was almost totally noise. Only the vaguestoutline of the person in the image was discernable.


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Figure B-3. Effect of diminishing light level on image integrity. Camera = Camera A. Distance = maximumoptical zoom. Light levels (in lux, from top left): Row 1 - 19.0, 7.5, 4.6, 3.3. Row 2 - 2.4, 2.4*, 1.5*, 1.0*. Row3 - 0.8*, 0.5*, 0.35*, 0.23*. Row 4 - 0.17*, 0.10* (* indicates effective light level while using 0.9 neutraldensity filter.)


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Figure B-4. Effect of diminishing light level on image integrity. Camera = Camera B. Distance = maximumoptical zoom. Light levels (in lux, from top left): Row 1 - 19.4, 7.6, 4.4, 3.4. Row 2 - 2.3, 2.3*, 1.5*, 1.0*. Row3 - 0.8*, 0.5*, 0.37*, 0.23*. Row 4 - 0.16*, 0.10* (* indicates effective light level while using 0.9 neutraldensity filter.)


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Figure B-5. Effect of diminishing light level on image integrity. Camera = Camera A. Distance = maximumdigital zoom. Light levels (in lux, from top left): Row 1 - 51, 31, 19.4, 7.7. Row 2 - 4.3, 3.4, 2.3, 2.3*. Row 3 -1.5*, 1.0*, 0.8*, 0.5*. Row 4 - 0.35, 0.24, 0.16*, 0.10* (* indicates effective light level while using 0.9 neutraldensity filter.)


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Figure B-6. Effect of diminishing light level on image integrity. Camera = Camera B. Distance = maximumdigital zoom. Light levels (in lux, from top left): Row 1 - 51, 31, 19.0, 7.6. Row 2 - 4.4, 3.5, 2.4, 2.4*. Row 3 -1.5*, 1.0*, 0.8*, 0.5*. Row 4 - 0.36*, 0.23*, 0.16*, 0.11* (* indicates effective light level while using 0.9neutral density filter.)


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Figure B-7. Effect of diminishing light level on ability of signal processing techniques to improve imageintegrity. Camera = Camera A. Distance = maximum optical zoom. Light Levels (in lux, from top left):Row 1 - 19.0, 7.5, 4.6, 3.3. Row 2 - 2.4, 2.4*, 1.5*, 1.0*. Row 3 - 0.8*, 0.5*, 0.35*, 0.23*. Row 4 - 0.17*, 0.10*(* indicates effective light level while using 0.9 neutral density filter.)


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loaded into a scientific computing package (IDL®),where they were individually scaled to maximizecontrast. All the images were summed on a pixel-by-pixel basis, and then that result was divided (alsopixel-by-pixel) by the number of frames (30). Theresulting image was once again scaled to maximizecontrast and then saved to a separate file. Each imagein figure B-7 is cropped10 from one of these averagedfiles.

While image processing using IDL® might be beyondthe average computer user, there are PC-basedgraphics-design software packages that can be used toachieve the same goal. One such package is Adobe®

Photoshop®. Using Photoshop®, one can read theTIFF images as separate files. For each image, thecontent can be copied and pasted into a layer of amaster image. Once in a master image, each layershould be adjusted using the “Auto Levels” feature

(pressing Control+Shift+L simultaneously), and theopacity should be adjusted to 100/number of framespercent. (For this reason it is best to try to have anumber of frames that will evenly divide into 100.)Once all layers have been adjusted, the layers can becombined (i.e., flattening the image) and the imagecan be saved.

B.2 Summary

This appendix has provided an overview of howdiminishing light can effect the images produced byvideo equipment. In doing this, it showed how thelow-light threshold of a camera or camcorder could bevisually assessed. Finally, a brief introduction intoimage enhancement was given showing useful infor-mation can be extracted from videotape footage evenwhen direct viewing does not reveal anything useful.

10The cropping was done only to provide a more compactdisplay in the figure.

U.S. Department of JusticeOffice of Justice Programs810 Seventh Street N.W.Washington, DC 20531

Janet RenoAttorney General

Daniel MarcusActing Associate Attorney General

Laurie RobinsonAssistant Attorney General

Noël BrennanDeputy Assistant Attorney General

Jeremy TravisDirector, National Institute of Justice

For grant and funding information contact:Department of Justice Response Center

800–421–6770

Office of Justice Programs National Institute of JusticeWorld Wide Web Site World Wide Web Site http://www.ojp.usdoj.gov http://www.ojp.usdoj.gov/nij

Documents

National Institute of Justice - NCJRS · National Institute of Standards and Technology (NIST) under the direction of A. George Lieberman, Program Manager for Communications Systems,