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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!
VISION 2014 – Industrial Vision Days
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.
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
The theory
Based on the imaging performance measurements, the ½” camera should perform
better than the ¼” camera
VISION 2014 – Industrial Vision Days
The practice
¼’’ CCD ½’’ CCD
at 10ms shutter
at 5ms shutter
at 2.5ms shutter
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
Easy comparison charts
VISION 2014 – Industrial Vision Days
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?
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
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?
VISION 2014 – Industrial Vision Days
Signal vs noise
IMX249 absolute sensitivity threshold
IMX249 will reach absolute sensitivity threshold at a lower light density
ICX414 absolute sensitivity threshold
VISION 2014 – Industrial Vision Days
Signal to noise ratio
IMX249 has higher signal to noise ratio at low lighting levels
In theory, IMX249 should perform better than ICX414
VISION 2014 – Industrial Vision Days
In practice…
In practice IMX249 does perform better!
at 2.5ms shutter
at 1ms shutter
IMX249 ICX414
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
High dynamic range example
IMX249
ICX414
VISION 2014 – Industrial Vision Days
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
VISION 2014 – Industrial Vision Days
Thank you Please visit us at Booth1b42