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You often see "dark, bias and flat fames applied" in an image credit line so it can be misleading as to what is really necessary. In a nut shell, if you subtract a dark frame that matches your light (or flat) frame ie. same duration and temperature, then no bias frame is required. You only need to use bias frames if you are scaling your darks so that darks taken under different conditions or of different lengths to your lights, are usable.
In my case with my very low noise H694 chip I see no improvement from subtracting darks anyway so I do neither darks nor bias and rely purely on dithering multiple light frames to remove noise. Of course this is not really possible with most other popular chips used in astroimaging cameras.
Mike
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