purpose: Creates a master bias from a set of bias frames.
description: The master bias is created from a set of raw bias frames, for which the highest and the lowest value for each pixel are rejected and the average of the remaining pixels is computed. The recipe should therefore not be used on fewer than 5 raw bias frames. The overscan regions, if present, are removed from the result. The master frame has 2 extensions, with the actual product being in the first extension and its errors being in the second extension.
At the end, the new master frame is compared with the corresponding certified master frame from the calibration database.
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