The Astrophotography Manual, 2nd Edition

Image Calibration and Stacking

Two strategies that go hand-in-hand to remove mean errors and reduce the noise level in the final image.

 

 

If a deep sky image was like a conventional photograph and did not require extensive image processing to enhance its details, calibration would be unnecessary. Unfortunately this is not the case and calibration is required to keep images at their best, even with extensive manipulation. The calibration process measures the consistent errors in an image and removes their effect. These errors are corrected by subtracting an offset and adjusting the gain for each image exposure. No two sensor pixels are precisely the same and the process of calibration applies unique corrections to each pixel in each image. ...