Bias and dark current from a graph of mean signal vs exposure time

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beans123
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TL;DR
I am attempting to find the bias and dark current from a graph of mean signal (per pixel) vs exposure time (sec) for 8 different dark frames.
I have a graph of mean signal (per pixel) vs exposure time (sec) for 8 different dark frames. I am being asked to find the bias in ADUs/pixel and the dark current in ADUs/sec/pixel and I am very confused on how I could get it. I know that the average of all of the mean signals is a rough guide as to what I should get for the bias per pixel but I'm very confused as to how to find the dark current from the graph.
 
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beans123 said:
I know that the average of all of the mean signals is a rough guide as to what I should get for the bias per pixel
Only if the dark current is very low. For example, if the bias is 100 ADU and the dark current is 0.1 ADU/s, and you take an exposure of 10 seconds, the mean pixel value of approximately 101 ADU is very close to the bias. But if the exposures are very long or the dark current is very large then you might wind up with a bias of 100 ADU but a mean pixel value of 150 ADU, in which case you would be off by 50% if you just went with the mean value.

beans123 said:
I have a graph of mean signal (per pixel) vs exposure time (sec) for 8 different dark frames.
Do these dark frames have the same exposure time, or different? If different, you can find the slope of the graph and extrapolate backwards to zero seconds exposure time to find the bias.