Video Surveillance is Useless

Peter KovesiSchool of Computer Science & Software Engineering

The University of Western Australia

Video Surveillance is Useless

Peter KovesiSchool of Computer Science & Software Engineering

The University of Western Australia

for Identification

Questions

• What image quality do we need for identification?

• How do you measure image quality?

• What is the image quality from a video camera?

• What is the effect on image quality when you: • record to video tape? • use frame grabbers of different quality?• use image compression?

Humans are very bad at recognizing unfamiliar faces

• Kemp, Towell and Pike (1997) tested the value of having photos on credit cards. When a user presented a card with a photograph of someone else that had some resemblance to the user, they were challenged less than 40% of the time.

• Bruce et al. (1999, 2001) have tested the ability of people to match good quality CCTV images of unfamiliar faces under a variety of scenarios. Correct recognition rates are typically only 70-80%.

Good quality photograph of target

Array of 10 good quality CCTV images

Bruce et al (1999).

Is this person in the array?If they are present match the person.

Good quality photograph of target

Array of 10 good quality CCTV images

When target was present in the array. 12% picked wrong person and 18% said they were not present (overall only 70% correct).

When target was not present in the array 70% still matched the target to someone in the array.

Bruce et al (1999).

Is this person in the array?If they are present match the person.

Automated Face Recognition is improving, but there is some way to go.

Face Recognition Vendor Test 2002 Identification performance results:

~ 90% for a database of about 100 individuals

~ 65-75% for a database of about 37,000 individuals

(US visa application photos taken with standardized equipment and with white backgrounds)

Identification performance appears to decline with database size in a log-linear manner.

€

PI (G) =1−α logGdatabase size

system performance parameter

• Even with good quality images face recognition performance, by human or machine, is poor.

• Surveillance video rarely provides good quality images.

• Even with good quality images face recognition performance, by human or machine, is poor.

• Surveillance video rarely provides good quality images.

What image quality is needed for face identification?

Image quality is defined by many attributes

• Minimum feature size that can be resolved

• Noise level

• Quality of luminance reproduction

• Quality of colour reproduction.

It is possible to build up any waveform by adding up a series of sine waves.

The human visual system analyses many aspects of images in terms of different frequency components.

Frequency Analysis of images

Minimum feature size that can be resolved…

(Nasanen 1999)

In humans it has been found that face recognition is tuned to a set of spatial frequencies ranging from about 20 cycles per face width down to about 5 cycles per face width.

The most important spatial frequency for face recognition corresponds to about 10 cycles/face width.

To be able to recognize with some confidence you need to be able to resolve 20 cycles/face width

20 cycles

10 cycles

5 cycles

Human Face Recognition

(Nasanen 1999)

In humans it has been found that face recognition is tuned to a set of spatial frequencies ranging from about 20 cycles per face width down to about 5 cycles per face width.

~ 160mm

20 cycles

10 cycles

5 cycles

Human Face Recognition

8mm

16mm

The most important spatial frequency for face recognition corresponds to about 10 cycles/face width.

To be able to recognize with some confidence you need to be able to resolve 20 cycles/face width

1951 USAF Chart

Groupings of 6 pairs of bars. Each successive set is half the size of the previous.

1951 USAF Chart

Groupings of 6 pairs of bars. Each successive set is half the size of the previous.

16mm

8mm

Eye charts also provide a simple way of measuring the minimum feature size that can be resolved.

20/20 Vision…

… or in metric, 6/6 vision

Snellen fraction66

Distance at which you should be able to read the line

Distance at which you can read the line on the chart

Minimum Angle of Resolution

88mm

72mm

58mm

36mm

44mm

6/6

6/12

6/24

6/48

Snellenfraction

Letter height

Number plate letters 80mm

Average eye spacing 65mm

logMAR Chart

9mm

18mm

Tests conducted with Pulnix TM6CN 1/2” CCD camera positioned 6m from the target.

Images were digitized directly from the camera using a Data Translation 3155 frame grabber (a good quality monochrome digitizer).

C-mount lenses: 4mm6mm8.5mm12.5mm 16mm

4mm lens

6mm lens

8.5mm lens

12.5mm lens

16mm lens

Camera image recorded to video, then played back and digitized. (Look at the USAF chart)

Camera image digitized directly.

Expect to lose quality when images are recorded to video

(cropped images taken with 12.5mm lens)

Compression is problematic.

Test targets survive compression well, but faces do not.

JPEG image quality 0 (14kB) JPEG image quality 4 (24kB)

Original PNG image (190kB)

JPEG images compressed using Photoshop. Image ‘quality’ can range from 0 - 12

JPEG (14kB) JPEG (24kB) Original

Faces do not survive compression well

Image from a Logitech webcam (640x480 image)

A Real Surveillance Camera Installation…

4.8 m

Image quality is defined by many attributes

• Minimum feature size that can be resolved

• Noise level

• Quality of luminance reproduction

• Quality of colour reproduction.

Luminance and colour cues are at least as important as shape cues

People perform about equally well using just shape information or just pigmentation cues.

O’Toole et al 1999see also Russell et al 2004

Fixed shapevarying

pigmentation

Fixed pigmentationvarying shape

Original faces

Luminance and colour cues are at least as important as shape cues

People perform about equally well using just shape information or just pigmentation cues.

Image compression typically quantizes colour information very heavily…

O’Toole et al 1999also Russell et al 2004

Fixed shapevarying

pigmentation

Fixed pigmentationvarying shape

Original faces

Conclusions

• Surveillance video, as it is currently used, is almost useless for identification.

• Surveillance cameras should be sited strategically to capture close ups of people as they pass through a constrained point, such as a doorway.

• Image quality standards should be developed for surveillance camera installations.

• Work is needed to develop measures of image degradation caused by compression.

Conclusions

• Identification errors will occur in biometric systems. As database sizes grow this will be an increasing problem.

Claims of misidentification have to be taken seriously.

• Face recognition performance is poor. It should probably only be used for verification of identity (one to one test), and not for identification (one to many test).

Conclusions

• Identification errors will occur in biometric systems. As database sizes grow this will be an increasing problem.

Claims of misidentification have to be taken seriously.

• Face recognition performance is poor. It should probably only be used for verification of identity (one to one test), and not for identification (one to many test).

Conan O’BrienUS talk show host

Tarja HalonenPresident of Finland

Conclusions

• Identification errors will occur in biometric systems. As database sizes grow this will be an increasing problem.

Claims of misidentification have to be taken seriously.

• Face recognition performance is poor. It should probably only be used for verification of identity (one to one test), and not for identification (one to many test).

Conclusions

• Identification errors will occur in biometric systems. As database sizes grow this will be an increasing problem.

Claims of misidentification have to be taken seriously.

• Face recognition performance is poor. It should probably only be used for verification of identity (one to one test), and not for identification (one to many test).