# Bias-frame correction

The bias-frame correction is a subtraction of a bias frame B from a source frame X to generate an output frame Y. Unlike the dark correction, scaling is not applied, because the bias is independent of exposure duration. The bias-frame correction is applied only in the advanced calibration scheme.

(1)Y(x, y) = X(x, y) - B(x, y)

The following statements describe how bad and overexposed pixels are treated:

- If a pixel is bad in either source frame or bias frame, it must be marked as bad on the corrected frame.

- If a pixel is overexposed in the source frame, it must stay overexposed after the correction.

- If a pixel is overexposed on the bias frame, it is marked as bad on the corrected frame.