Quote:
Originally Posted by gregbradley
Not sure about that technically. Why would you subtract a master bias from a master dark? The master dark already has the master bias component in it and you would want that when you subtract it from your light as the light would have the white edge in it.
As I understand it bias are more for flats unless you want to scale your darks which is handy at times.
Greg.
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Hi Greg,
I don't normally subtract a bias from a master dark! Spacenoob said I should try that as a test which I did and got the predicted result.
I did experiment by subtracting a bias frame from my lights and that seemed to do as good a job removing the white line as a master dark. I just wonder about the advantage or disadvantage of doing that given previous statements by others on this forum that dark calibration can add more noise than it removes. Also, Terry Platt responded to me and said:
"It’s a very slight overshoot in the CCD amplifier, caused by the sudden DC change at the start of each line. It’s a ‘bias’ artefact and is completely removed by a bias subtraction."
Peter