View Full Version : Auto white balance, auto exposure processing?

November 15, 2006, 18:53:25

I have a camera DFK 41AF02 which is mounted on the helicopter to survey area and return images at a rate of 1 image/sec. To reduce the CPU load I interrupt video stream using
ICImagingControl1.LiveCapturePause:=True (or False);

If in the camera properties I enable AutoWhiteBalance, AutoExposure, AutGain etc, then It takes camera about 10 iterations to adjust these parameters (which is equivalent to 10 second) which is too slow for that application. For example, moving from sandy desert landscape (light background) to a forest (dark) may occur in a matter of a seconds, and camera does not adjust itself quickly enough.

Q1. Where processing of the image and subsequent adjustment of the camera settings is actually performed: onboard (in the camera itself by means of FPGA/microcontroller) or inside the PC by means of WDM driver?

Q2. Why camera settings adjustments are so slow? Could iterations converge more quickly? To be more precise: I would expect that a single image should be sufficient to estimate an exposure for the next one. Is it worth trying to implement such an algorithm inside the PC (just guessing)?


Stefan Geissler
November 17, 2006, 10:44:35

Q1: The processing is in the camera.

Q2: You would need some more images to calculate exposure and white balance, because you set a value and it will be used for the next image and then calculated again. You understand, that you can not set the changes to strong, because the oscilation of brightness from one image to the next would be to much. Thus the "iteration" is done using more then one image.

I guess it is not worth to write an own algorithm in the computer, because you would meet the same problems I described above. If you have time, then just try it, it could be interesting.

November 17, 2006, 14:58:38
Hi Stefan,

thank you for reply on my inquiries and support. I am learning more about imaging with your help.

>you can not set the changes to strong,
>because the oscilation of brightness..
Yes, I noticed oscillations on very short exposure, when returned image is dark and auto exposure is ebabled. What I don't understand is why I see minor oscillations even when ALL 'Auto' options are disabled! I would expect a still image.

I worked a lot with PID controls and those oscillations (with Auto options) remind me 'underdumped' system (integer part is too low or zero). I also learned that some digital imaging manufacturers (e.g. NIKON) use a lookup tables rather than iteration procedure, so when you point and shoot an image, the exposure and iris (or gain) are set based on information gathered from ~10 small parts of the image just right before the trigger. Though it is rather ambitious to realize such approach in general case, it is quite doable in if, say, only 2 parameters are to be adjusted (exposure time and gain).


Stefan Geissler
November 17, 2006, 15:21:19

Please excuse me that our engineers have other experiences in camera building than you. If it would be so simple, they would have implemented it as you suggested.