How do pixel values relate to gain exactly?

I am using FlyCapture2 SDK with a Blackfly GigE camera. I am experimenting with the "gain" setting. In "absolute" mode, the gain ranges from -1.5 dB to 40.5 dB. When I take a series of images of a uniform-color field at increasing gain values in that range, I see that the average pixel value grows at what appears to be an exponential rate. What rate is this exactly? That is, what is the definition of the dB that "gain" represents? If dB = 20 * log(V/V0), where V0 is the input voltage at gain = 0, then I would expect the average pixel values to increase faster than I'm measuring. For example, if I measure an average pixel value of ~19 at gain = 0, I would expect the average pixel value as a function of gain (g) to be = 19 * 10^(g/20), but that curve is steeper than what I measure. Here is a plot:

Official comment

TDY_Manuel

Community team

November 14, 2024 08:03

Could you please try again with a higher brightness setting to prevent the lower part of the histogram from being cut off? Also, please make sure gamma is turned off. Best use a RAW pixel format.

If that doesn't help, could you please open a support ticket on https://flir.custhelp.com/app/ask ?

September 17, 2024 07:45

Hello MJ,

You are right, we use a 20 log rule for our gain setting. I'm wondering if the Brightness setting could cause this. Could you please check if it was set to 0?

Best regards,

Manuel

November 13, 2024 21:43

Thanks for the reply and sorry for the delay. I'm unable to check what the settings had been, but I re-ran the experiment, first setting the Brightness to 0, and got essentially the same results.

November 14, 2024 22:59

That was the ticket. I hadn't considered the gamma and had been using RGB8 mode so that it was easy to handle the separate color data. When I switched to RAW8, the theory and experimental values line up very closely.

Thank you for the help.

How do pixel values relate to gain exactly?

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