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Hello,I have CCD images with overscan region. When I use ccdproc, IRAF subtracted my images with overscan region and bias images. My question is, since the "bias" is already inside (embedded in) the "overscan", isn't it redundant to subtract the bias twice from the images?Normally if I have a set of science, dark, bias, and flat frames, I just subtract the darks from the science images. I did not use bias images in subtraction since it is already included in the darks - I just use them for stability check.Thanks,
Hanin.

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IRAFNET PC-IRAF Revision 2.13-BETA2 Wed Apr 19 21:21:13 MST 2006 on Ubuntu 7.04

Hello,Overscan corrections are used to track very short term electronic drifts; on the time scale of an exposure. Bias or dark frames are also overscan corrected to leave any more stable 2D pattern of dark counts or electronic zero point variations for removal from the overscan corrected science exposures.Yes, it is generally the case that one uses dark calibrations in place of bias or zero frame calibrations.So you should use overscan and dark calibrations.Yours,
Frank Valdes