Introduction

The standard calibration algorithm executes the following steps for each raw data image (if requested, see the dialog window in figure 1):

  1. Subtracts the sky image from the raw image.
  2. Divides the result by the flatfield.
  3. The value of each bad pixel is replaced by a value, calculated from some neighbour pixels.

Important:

It depends on the algorithm used for the reconstruction step if it is allowed to subtract the sky background or not. For example, the Richardson-Lucy deconvolution algorithm uses a sky-subtracted psf but a target image which must contain the sky background. In this case, the sky background must be kept and subtracted later during the psf preprocessing step.
Calibration setup dialog
Figure 1: Standard calibration setup dialog.

The defect pixel interpolation is provided by an algorithm which uses up to two pairs of good pixels. The pixels of a pair are on the opposite side of a defect pixel, and an interpolation schema is used to calculate the replacement value.

Additional information: