Newbie trying to understand flats

[rppass]

Suppose I take a series of flats and over the course of time the lighting decreases (e.g., sky flats).  What is the process that PI uses to combine these images into a master calibration?  One naive way is to scale each image so the median is the same and then combine them, but I am wondering what PI does.

Thank you,
Ralph

[RickS]

See the section on Normalization in the documentation for ImageIntegration.  Read all the rest while you're there