how to select the right camera using the emva 1288 standard · how to select the right camera using...

How to select the right camera using

the EMVA 1288 standard ?

A. Darmont - [email protected]

J. Caron - [email protected]

Agenda

• EMVA 1288 motivations

• Basic principles

• Measurements

• Template camera datasheet

• Examples

20 Sept. 2017 ENOVA Show | Paris

EMVA 1288 motivations

• European Machine Vision Association initiative - www.emva.org

• Define a unified method to measure, compute and present specification parameters for cameras and image sensors used for machine vision applications

• Data presentation guidelines for easy comparison of cameras and image sensors

• First release in August 2005


http://www.emva.org/

Basic principles

● Based on mathematical models

● Provides test methods to robustly extract device parameters

● All parameters are based on physical quantities (no lux, lumen, foot candle)

● Defined so that little freedom is left to the user → fair reporting, allows for direct comparison of devices

● Reproducible and repeatable measurements


Basic principles

● 3 basic formulas

– Linear signal model– Photon Transfer Method– Signal-to-Noise ratio


Basic principles


Basic principles – Linear Signal Model


● Linear Signal Model

● Analyzed by the photoresponse plot

● A linear fit through the non-saturated (< max variance) data points gives and

y= y , darkK AhcEtexp

y= f E t exp

y , darkK

Ahc

Basic principles – Linear Signal Model


Photoresponse Plot

0.00E+000

5.00E+001

1.00E+002

1.50E+002

2.00E+002

2.50E+002

3.00E+002

0.0E+0 2.0E+3 4.0E+3 6.0E+3 8.0E+3 1.0E+4 1.2E+4 1.4E+4

Nbr Photons

DN

[8b

]

Dark Signal

Bright Signal

Dark corr Signal

Basic principles – Photon transfer method


● Photon transfer method

● Analyzed by the photon transfer plot

● A linear fit through the non-saturated data points gives and

y2=K2d

2q2K y− y ,dark

y2= f y− y , dark

K K 2 d2 q

2

Basic principles – Photon transfer method


Photon Transfer Plot

-1

0

1

2

3

4

5

6

0.0E+0 5.0E+1 1.0E+2 1.5E+2 2.0E+2 2.5E+2 3.0E+2

Dark corr Signal [DN]

Var

ain

ce [

DN

² /

8bit

]

Dark corr Variance

Linear Fit

Basic principles – image acquisition

● Two images for each exposure

● Large number of images at 0% and 50% exposure (reason will be explained later)


www.aphesa.com

Image acquisition0% 17% 34% 50% 67% 84% 100% 117%

Ave

rage

Sen

sor

outp

ut %

Light input %

www.aphesa.com


Ave

rage

Var

ianc

e

Light input %

www.aphesa.com


...

L+2 images

...

L+2 images

Basic principles – SNR


● Signal-to-Noise ratio

SNR p= p

d2

q2

K2 p

SNRideal p= p

Basic principles – SNR


log2 SNR [bit]

51 10 151

5

log2 µp.min log2 µp.sat

log2 µp [bit]

log2 SNRmax

slope = 0gain noisedominated

Basic principles – Non-uniformities

● Spatial variance → overall measure of spatial non-uniformity --> DSNU & PRNU

● Spectrograms → patterns of periodic signal variations

● Defect pixels


Basic principles – Total noise SNR


SNR p= p

d2DSNU 1288

2

q2

K2 pPRNU 1288

22 p2

Basic principles – Other parameters

● Sensitivity

● Dynamic Range

● Dark current

● Dark current doubling temperature

● Linearity

● Spectral response

● (Response delay)

● (Shutter efficiency)

● (RTN)


Basic principles – Monochronatic light source

● Uniform monochromatic light source

● F/8

● Many aspects of its implementation are left to the user

● Several intensity variation methods possible


Monochromatic Light Source


● Properties

– At most 3% uniformity error within the sensor's area

– FWHM of at most 50nm– Stable of time– Calibrated within 3 to 5% for absolute irradiance at

least every second year.


Template datasheet

● Standard format for all sensors and cameras

● Summary datasheet followed by detailed plots

● Mandatory

● Must be used in conjunction with the EMVA1288 logo

● Must be made available to the public for any sensor or camera that complies with the EMVA1288 standard and uses the logo


Template datasheet

● Page 1

– Camera/sensor information– Operating point information– Spectral response plot


Template datasheet

● Page 2

– Operating point information– Photon transfer plot– SNR plot– Table (on the right) with all

mandatory numeric results● Pages 3 to 9 : all measured and

calculated plots


www.aphesa.com

Selecting an Image Sensor or a CameraStart with simple application requirements

– Irradiance from Brightest and Darkest points of the scene– Linearity requirements– Is image processing available for sensor corrections– SNR requirements– Wavelength of illumination / Spectrum of the scene

www.aphesa.com

Selecting an Image Sensor or a Camera

– Maximum acceptable exposure time– Resolution– Operating temperature

www.aphesa.com


Irradiance from darkest point– Dark noise SNR=1 point (or SNR=3 or 5 etc)→

Irradiance from brightest point– Saturation capacity– Dynamic range

Linearity– Linearity error

www.aphesa.com


Operating temperature– Dark current at room temperature– Dark current doubling temperature

www.aphesa.com

Defects found using the standard

Reminder: basic principle = model ideal behavior, make measurement, extract paremeters.

What happens if the data does not follow the model– Some measurements may be incorrect– More important: the device being tested is far from ideal

• On-purpose check datasheet→• Design errors and defects design validation for the →

sensor/camera design company.

www.aphesa.com

Defects found using the standard

Conclusions

● Users: always request EMVA1288 data from your suppliers

● Suppliers: be ready to provide EMVA1288 data to your customers

● Save evaluation and comparison time with the EMVA1288 standard


THANK YOU

Questions?

how to select the right camera using the emva 1288 standard · how to select the right camera using...

Documents