Tools tab help

You don't have to draw boxes outside of stars, APP is smart enough to see what a star is and what background. I usually stretch the preview a lot (30%, with the preset box on the right of the screen) and up color saturation a lot. This shows me which areas seem true background and what the problem parts in the image are. I then draw just 4 or 5 rather big boxes around the image and press "calculate". Then I check the result and based on that either create new boxes or I add a few, it's not needed to draw a lot of boxes. Gradients should be gradual across the image, not all over the place.

Thanks Vincent, so do you draw the boxes only in the problem areas? I'm trying to understand where I should do them, in the problem areas, in the ok areas (so APP can take these as 'what the background should be like') or across an area which encompasses both so a gradient is captured in a box.

Thanks
Ed

You should avoid drawing them on the area's with nebulosity, that's why I overstretch to make that more visible. You can just place a few all over (start with 4-5, doesn't really matter what it looks like, as long as it is background), check the result and the possibly place a few more. APP will built a model of the gradients (you can see that model by clicking on "show corrected image", that should show some gradual gradients and if it then looks good to your eye, it's likely fine already. When background consists of other light pollution, it becomes more tricky and you may have to go back and forth a bit with placing boxes and checking the results.