The following tutorial is geared to help an astrophographer know how to create a synthetic flat to deal with image issues such as irregular pattern noise and other blemishes that aren't discovered till after data collection and image stacking has already occurred.
The following steps should be a good "cheat sheet" for a user to follow as they learn the concepts taught in this tutorial:
Making a Synthetic Flat in PI: (start with a stretch image - non-linear)
1. Starless Color Image (use starnet++ or starexterminator to get a color starless image)
2. AdvStarMask
3. AutoStrech StarMask -- apply to HistoGramTransformation and apply
4. Binarize (set K value on dim star and then apply)
5. Then CTRL-...