View Full Version : How does auto-exposure works?

August 22, 2007, 11:38:36

I often use auto-shutterspeed (not gain).
I wonder how this function realy works..

Is it evaluating the frame it receives from the camera?
Average weighting or something?
Or is it just following a certain value, set by the software.

And this value.. what is this?
Sometimes I must set it to 600, sometimes to 150 to have a good auto exposure. I do not understand this.

Thank you in advance


Sascha Schmidt
August 22, 2007, 13:44:34
Hallo Fred,

Simplified, the auto-exposure-algorithms analyze the image lightness and extend/reduce the exposure-time in consideration of the auto reference value.

For example, if the automatic-algorithms detects an dark image, the exposure time will be raised.
The auto reference value can be considered as the fine tuning for the auto exposure algorithms.

August 22, 2007, 13:51:01
Hello Sascha,

Thank you for the fast answer. :)

But how is the image brightness analyzed?
White peaks? Average grey levels???
And is this analyzing done in the camera or by the IC Capture software?

Thank you in advance,

Sascha Schmidt
August 22, 2007, 14:59:54
Hallo Fred,

But how is the image brightness analyzed?
The algorithms adds up exclusive pixels to specify the brightness by the average brightness of these pixels.

And is this analyzing done in the camera or by the IC Capture software?
The auto-exposure-algorithms is done by the camera (firmware).

August 22, 2007, 15:17:59

Thank you for explaining!


August 29, 2007, 22:18:46
I have a DFK21AF04 and I bought a lens with DC iris (if that's the correct name for it).

The reason being that for my application, I want constant shutter speed (camera will be mounted on a rough terrain vehicle), so the aperture would be the other parameter to control.

Obviously the camera doesn't have a connection for the dc-iris control, so I will have to develop the electronics and the feedback control loop myself.

The question is: have you guys seen such an application before? Is it something feasible to implement? Any hints?

Stefan Geissler
September 3, 2007, 10:29:44
Hello padu,

Our zoom cameras do this internally. The have an auto iris functionallity. But I am not able to tell you how the algorithm and iris control works. I am sorry for this.