Thank you @supernov ?
There is off course a big difference between
- images with lots of background and little or no nebulosity, like your recent M81/M82 data
- or data full of nebulosity
A correction is simple and quickly done in the first case, and that could be more or less automated.
But in the second case, you will need to work step by step, I’ll make a video showing this on difficult data with lots of nebulosity ?
One more tip, placing the select boxes evenly over the image helps, since each select box has a weight in the model calculation.