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

Transcription

1 How to select the right camera using the EMVA 1288 imaging performance standard Vladimir Tucakov - Director of Business Development 2014 VISION Industrial Vision Days

2 Presentation outline Introduction on why imaging performance matters Detailed explanation of imaging performance measurements Introduction of the EMVA 1288 Standard Introduction of Point Grey s image sensor review document Examples of how to use the data to select a camera

3 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!

4 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.

5 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

6 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:

7 LIGHT Shot Noise = Number of photons Photons per μm 2 Quantum Efficiency (%) Temporal Dark Noise (e-) Saturation Capacity (e-) Pixel Size (μm) WELL Signal (e-) Gain (e-/adu) = GREY SCALE (16-bit)

8 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

9 So, will ½ sensor help? EMVA 1288 results: Camera 1/4 Camera (FL3-GE-03S1M-C) 1/2 Camera (BFLY-PGE-03S3M-C) Sensor Pixel size (µm) Quantum Efficiency (%) Temporal Dark Noise (e-) Saturation Capacity (e-) ICX ,508 ICX ,949 ¼ CCD has better quantum efficiency and lower noise* ½ CCD has a bigger pixel and larger saturation capacity* Which one will do better?

10 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

11 Signal and noise of the ¼ camera Temporal Dark Noise and Shot Noise Absolute sensitivity threshold This graph shows the signal and noise of the ¼ camera NNNNNNNNNN = (TTTTTTTTTTTTTTTT DDDDDDDD NNNNNNNNNN) 2 +(SSSSSSS NNNNNNNNNN) 2

12 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

13 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

14 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

15 The theory Based on the imaging performance measurements, the ½ camera should perform better than the ¼ camera

16 The practice ¼ CCD ½ CCD at 10ms shutter at 5ms shutter at 2.5ms shutter

17 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

18 Easy comparison charts

19 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?

20 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

21 We repeat the exercise! EMVA 1288 results: Camera Sensor Pixel size (µm) Quantum Efficiency (%) Temporal Dark Noise (e-) Saturation Capacity (e-) BFLY-PGE-03S3M-C ICX ,949 BFLY-PGE-23S6M-C IMX ,691 ICX414 CCD has a larger pixel* IMX249 has larger QE, less noise and larger saturation capacity* Which one will do better?

22 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?

23 Signal vs noise IMX249 absolute sensitivity threshold ICX414 absolute sensitivity threshold IMX249 will reach absolute sensitivity threshold at a lower light density

24 Signal to noise ratio IMX249 has higher signal to noise ratio at low lighting levels In theory, IMX249 should perform better than ICX414

25 In practice IMX249 ICX414 at 2.5ms shutter at 1ms shutter In practice IMX249 does perform better!

26 Apparent sensitivity ICX414 will reach saturation at about 700 photons/µm 2 IMX249 will reach saturation capacity at about 1,250 photons/µm 2 ICX414 will appear brighter, but IMX249 will have higher dynamic range and better low light performance

27 High dynamic range example ICX414 IMX249

28 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

29 Thank you Please visit us at Booth1b42