View Full Version : Laser beam profile

May 15, 2009, 12:20:47
I'm using the DMK-21BU04 to record the laser beam profile in a 1km free space optical link. When I set parameters to star capture, I've notice that if I change the value of 'Auto Reference' in the properties dialog I get different values of each pixel.

The thing is that this parameter's range is 0-255, and if I choose 0 I get the dimmest image, and if I use 255 I get an extremely bright image, in which the background becomes too large. When I look for documentation on this paremeter, I didn't found what kind of operation it performs on the image. It would be of much help if someone could clarify this to me.

Another question is regarding the Gamma value. As my camera is USB I would like to know which value of gamma give me the most linear response. Currently I'm using 100 (the default option).

Stefan Geissler
May 15, 2009, 13:44:29

The auto references determines the brightness to be achieved by the exposure automatic.

100 is no gamma correction. Than means the Gamma value is 1 (Iin = Iout^Gamma)

May 15, 2009, 15:04:21
First of all thanks for your rapid response.

I still have some questions. What do you mean by "...the brightness to be achieved by the exposure automatic"

I am not using the exposure in automatic. So what would be the difference in the image (how each pixel is affected) between a image taken with AutoReference in 0 and another one with 128.


Stefan Geissler
May 15, 2009, 15:28:19
The automatic exposure has a criteria, that determines, how bright the resulting image should be. This is meant by brightness. The gain - automatic is also influenced by this value.

What the difference is exact, is not specified, and in fact, I never measured this on my own. This is some of the secrets of the camera engineers :-)