ABSTRACT
Longer and multiple exposures demand full image calibration and integration to improve image quality. This chapter recaps the benefit of averaging multiple images to reduce their random noise level and goes into the details of image calibration (also known as pre-processing or linear processing). Although calibration is an essential activity for deep-sky imaging, at the same time, it can be useful in any situation where a sensor is operating at its limits. The calibration process resolves the repeating errors by characterizing the optical transmission path and sensor readout for a specific optical configuration (including aperture, filters and camera rotation, sensor temperature, ISO setting and exposure duration). Some consider flat frame calibration as optional, for the reason of keeping the process simple. It often depends on the issues one sees during image processing. DeepSky-Stacker stacks images, but it can calibrate and align images first before stacking, and more besides.
