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What is Gain?

Started by jimhp29401us, 01/05/2004 01:54PM
Posted 01/05/2004 01:54PM Opening Post
Hello everyone. When I am imaging with my Toucam Pro I play with the gain to get the best image on the screen before I start actually recording the AVI. Can anyone explain "gain"? Should I try tor higher gain with lower brightness or the reverse? Thanks for any help.

Jim Phillips
Posted 01/05/2004 03:03PM #1
Hi Jim -

I'm sure someone can give a better technical explanation, but from my understanding - gain is electronic amplification of the levels in the image without adding signal - so with gain comes pain - noise.

In perfect seeing, the best image would come with the lowest gain setting that produces a sufficiently bright image. In the real world it's more complicated. In average seeing, using a higher shutter setting will freeze details that can't be captured otherwise - but to move to a faster shutter will require gain to be increased. I find that I still fiddle with these settings every night I go out - almost as much as I fiddle with the focus! But the proper marriage should be a function of the object brightness, aperture and seeing.

Just my .02!


Alan Friedman
Posted 01/05/2004 07:01PM #2

You could think of it as the electronic equivalent of ISO. It’s the amplification factor between the CCD and the Analog to Digital converter inside the camera. The amount of signal that’s captured doesn’t change. When you turn up the gain you’re amplifying that signal more before it’s converted to a digital signal. You’re also spreading out the signal and creating a larger Quantification noise which is the individual steps between each signal level.

Let’s say that you’ve got a CCD with a full well capacity of 10mV and your digital to analog converter accepts a signal between 0 and 10V. You capture enough photons to generate a 2mV signal. You amplify it by 1000 which converts it to 2V which is then feed to the A/D converter. If you turn up the gain to 1500 then the signal that the A/D converter sees is 3V. You get a larger signal out but you haven’t really captured any more data. You’ve just spread it out more and that makes the steps between discreet levels courser.