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Hi Greg,
This is what Stan wrote:
"Sony CCDs have remarkably uniform dark current (pixel-to-pixel) and often do not need dark subtraction. In fact, dark subtraction may inject more noise than it cures (that's why it is advisable to use a very high quality dark). But when avoiding dark subtraction, it is necessary to remove the bias or bias level (pedestal) in order for flat fielding to work properly. And it might be useful to mask out a few consistently bad pixels. This can be implemented in CCDStack."
So, I don't think he is talking about the choice of bias subtraction whilst making a dark vs. doing the bias subtraction when running the calibration tool. I think he is speaking about actually using a dark (or a bias frame as a dark).
Yes, you can make a pixel map and map the columns. You just use different rejection tools. There are examples of doing it free hand in Adam Block's tutorial.
Peter
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