bablokb
Posts: 25
Joined: Fri Nov 07, 2014 7:45 am

AWB off results in severe underexposure

Fri Nov 07, 2014 8:52 am

Hi all,

I'm using a NOIR camera-module and have some problems when AWB is turned off. When I set awb to off (e.g. raspistill --awb off -o test.jpg) the shutter-speed will be 1/5587 (at least that's what is recorded in the exif-data). The image is therefore nearly black. Same happens with python pi-camera.

Since I also have a LCD screen attached, I'm using a custom kernel, but the system is quite current (from Sept 2, 2014). Kernel is 3.12.26+. So this issue might be related to the special kernel/firmware of my system.

So my questions are: can anybody confirm the issue with a current stock raspbian? Can I somehow query the camera-firmware? Is it possible to upgrade the camera firmware independently of the kernel?

Thanks in advance, Bernhard

ethanol100
Posts: 587
Joined: Wed Oct 02, 2013 12:28 pm

Re: AWB off results in severe underexposure

Fri Nov 07, 2014 10:10 am

You need to specify the gains with -awbg 1,1 where the first number is for the red and the second for the blue gain. The values are in the "0<x<=8". These are set to 0 if not specified and that is not what you want.

bablokb
Posts: 25
Joined: Fri Nov 07, 2014 7:45 am

Re: AWB off results in severe underexposure

Fri Nov 07, 2014 12:39 pm

Ok, my understanding was that turning automatic (!) white balance off is something different than setting white balance manually. It would be more logical if setting gains to 1,1 would be the default for -awb off. Or rename "off" to "manual". Now the user has to know that for every setting _except_ off he should not set gains manually, but for off he has to set gains manually.

Also, I see no reason why tinkering with white balance changes the shutter speed (in case of AWB off very drastically).

Bernhard

ethanol100
Posts: 587
Joined: Wed Oct 02, 2013 12:28 pm

Re: AWB off results in severe underexposure

Fri Nov 07, 2014 1:11 pm

I think

Code: Select all

-awbg, --awbgains       : Set AWB gains - AWB mode must be off
is quite clear.
The auto white balance is just an algorithm, which changes the the white balance automatically. If it is off, it should be clear that this is the manual mode. The white balance always depend on the lighting, and setting it to 1 is just useless.

Have you looked in the forum before posting? There are a lot of threads about awb?

And the auto exposure and auto white balance need to work together, setting wrong values for one will clearly change the other.

Just don't use it, if you are not comfortable with it. A normal user should be happy with awb auto and exp auto. :roll:

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