How to select the right camera using the EMVA 1288 imaging ... · How to select the right camera using the EMVA 1288 imaging performance standard ... Dark noise and Shot ... the camera

How to select the right camera using the EMVA 1288 imaging performance standard

Vladimir Tucakov - Director of Business Development 2014 VISION – Industrial Vision Days

Presentation outline

Introduction on why imaging performance matters 1

Detailed explanation of imaging performance measurements 2

Introduction of the EMVA 1288 Standard 3

Introduction of Point Grey’s image sensor review document 4

5 Examples of how to use the data to select a camera

VISION 2014 – Industrial Vision Days

Do you feel lucky? Is your job to select a camera for a machine vision application?

License plate recognition? Pharmaceutical identification?

Question: Is considering resolution, frame rate and interface sufficient to select the correct camera?

Answer: Only if you are lucky!


So you pick a camera… You determine that a VGA camera with a ¼” CCD running at 30 FPS is

sufficient in your application

You purchase a Point Grey Flea3 GigE camera with the ICX618 CCD for €375

Your initial tests show that you are able to get meaningful data from the camera!

at 10ms shutter*

* Every effort has been made to make a fair comparison between cameras. This includes using same lenses, or lenses with the same field of view and F number, camera settings such as shutter times, gamma settings, etc. Images used in this

presentation have been adjusted for display purposes without changes to the underlying data.


But… …when your objects start moving you need to reduce the shutter time

and you are no longer able to get the information you need

at 5ms shutter

at 2.5ms shutter


Will another camera help?

Will going to a larger VGA sensor help, a 1/2’’ CCD perhaps? e.g. Blackfly with the ICX414 CCD for €375

To answer this question we need to consider the imaging performance of the two cameras

We will use the EMVA 1288 standard which defines what camera performance to measure, how to measure and how exactly to present

the results

Full standard definition available at: www.emva.org

http://www.emva.org/

Signal (e-) Gain (e-/ADU)

Saturation Capacity (e-)

Photons per μm2

Number of photons

Shot Noise =

Quantum Efficiency (%)

LIGHT

Temporal Dark Noise (e-)

GREY SCALE (16-bit)

= Pixel Size

(μm)

WELL


Summary of parameters Measurement Source Definition Influenced by Unit

Shot noise Fixed Square root of signal Caused by nature

of light e-

Pixel size Fixed Well, pixel size… Sensor design µm

Quantum efficiency Primary Percentage of photons converted to

electrons at 525nm Sensor and camera

design %

Temporal dark noise (Read noise)

Primary Noise in the sensor when there is no

signal Sensor and camera

design e-

Saturation capacity (Well depth)

Primary Amount of charge that a pixel can hold Sensor and camera

design e-

Signal to noise ratio Derived Ratio of signal to noise including

shot and read noise N/A dB, bits

Dynamic range Derived Ratio of signal to noise including

only read noise N/A dB, bits

Absolute sensitivity threshold

Derived Number of photons needed to have

signal equal to noise N/A Ƴ

Gain Derived Parameter used to convert the signal

in electrons to ADUs (better known as grey scale)

N/A e-/ADU


So, will ½’’ sensor help?

EMVA 1288 results:

¼” CCD has better quantum efficiency and lower noise*

½” CCD has a bigger pixel and larger saturation capacity*

Which one will do better?

Camera Sensor Pixel size (µm)

Quantum Efficiency

(%)

Temporal Dark Noise

(e-)

Saturation Capacity

(e-) 1/4’’ Camera

(FL3-GE-03S1M-C) ICX618 5.6 70 11.73 14,508

1/2’’ Camera (BFLY-PGE-03S3M-C) ICX414 9.9 39 19.43 25,949


Signal vs. light density Signal = Light density x (Pixel Size)2 x Quantum Efficiency

Saturation capacity

It is clear that the ½” camera generates more signal than the ¼” camera


Signal and noise of the ¼” camera

This graph shows the signal and noise of the ¼” camera

Absolute sensitivity threshold

Temporal Dark Noise and Shot Noise

𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁 = (𝑇𝑇𝑁𝑁𝑇𝑇𝑇𝑇𝑁𝑁𝑇𝑇𝑇𝑇𝑇𝑇 𝐷𝐷𝑇𝑇𝑇𝑇𝐷𝐷 𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁)2+(𝑆𝑆𝑆𝑁𝑁𝑆𝑆 𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁)2


Signal and noise of the ½” camera

This graph shows the signal and noise of the ½” camera Noise includes the Temporal Dark noise and Shot noise


Comparison of the two cameras

½” camera will reach absolute sensitivity threshold at a lower lighting level

This graph shows the signal and noise of both cameras In addition to more sensitivity, ½” will detect light at lower light density


Signal to noise ratio

This graph shows the Signal to Noise ratio at low light levels Note that the ratio is expressed in linear scale, not dB


The theory

Based on the imaging performance measurements, the ½” camera should perform

better than the ¼” camera


The practice

¼’’ CCD ½’’ CCD

at 10ms shutter

at 5ms shutter

at 2.5ms shutter


Point grey’s sensor review

Point Grey published the industry’s most comprehensive review of camera sensors

The camera review consists of results for more than 70 different part numbers tested based on the EMVA 1288 Standard

The document contains raw data and easy to understand comparison charts


Easy comparison charts


Even faster? What if you find out that in your application you need even faster

shutter times (e.g. conveyor belt speed was increased)?

You test the ICX414 camera and discover that it is unable to provide you with the sensitivity you need

at 1ms shutter

You consult the camera sensor review document and discover that

none of the VGA sensors would perform better than ICX414

What to do?


Global shutter cmos?

At Vision 2014 you discover the new Sony IMX249 global shutter CMOS sensor (same imaging performance as IMX174, but lower

frame rates and price)

You learn that it has excellent imaging performance and it costs only €379 in Point Grey's Blackfly camera

While the IMX249 is a 2.3MP, 1’’ sensor, you can use a VGA region of interest and the same lens as what you used on your 1/4’’ camera

So, will this camera outperform the ½’’ ICX414 CCD?

To answer this question we have to repeat the exercise we did with the ¼’’ CCD


We repeat the exercise!

EMVA 1288 results:

ICX414 CCD has a larger pixel*

IMX249 has larger QE, less noise and larger saturation capacity*

Which one will do better?

Camera Sensor Pixel size

(µm)

Quantum Efficiency

(%)

Temporal Dark Noise

(e-)

Saturation Capacity

(e-)

BFLY-PGE-03S3M-C ICX414 9.9 39 19.43 25,949

BFLY-PGE-23S6M-C IMX249 5.86 77 6.83 32,691


Signal vs light density

ICX414 generates higher signal than IMX249 at same lighting levels

Does this mean that it will perform better at low light levels?


Signal vs noise

IMX249 absolute sensitivity threshold

IMX249 will reach absolute sensitivity threshold at a lower light density

ICX414 absolute sensitivity threshold


Signal to noise ratio

IMX249 has higher signal to noise ratio at low lighting levels

In theory, IMX249 should perform better than ICX414


In practice…

In practice IMX249 does perform better!

at 2.5ms shutter

at 1ms shutter

IMX249 ICX414


Apparent sensitivity

ICX414 will reach saturation at about 700 photons/µm2

IMX249 will reach saturation capacity at about 1,250 photons/µm2

ICX414 will appear brighter, but IMX249 will have higher dynamic range and better low light performance


High dynamic range example

IMX249

ICX414


What have we learned?

We learned why imaging performance matters in camera selection

We reviewed the key imaging performance parameters

We learned how to use EMVA 1288 standard and Point Grey’s sensor review document to select cameras

Learned how to determine whether a camera will have better performance at low light - remember to square the pixel size!

We learned that imaging performance results can narrow down camera selection…

… but can not replace tests within the application environment


Thank you Please visit us at Booth1b42

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How to select the right camera using the EMVA 1288 imaging ... · How to select the right camera using the EMVA 1288 imaging performance standard ... Dark noise and Shot ... the camera