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Hey everyone,

I feel like I've got a good workflow down for processing my astro images, but there's one thing that's still bugging me - background (or gradient) removal.

The only tool I've found that offers to do it so far is IRIS, and while their 'remove gradient (polynomial)' works well for some photos, on others it seems to just add to the overall noise. For example, here's an M101 from last night with a visible background gradient from the top left:


If I could get rid of the gradient, I think this would be a really decent photo. So, if I run it through IRIS and their gradient remover, I get this:


It's done a decent job in the top left, but it seems to have inverted the gradient so that it's now starting from the bottom right. It also seems to always introduce fairly nasty banding artifacts which I think are worse than the original gradient.

While the gradient remover doesn't seem to be much help, I have found that the 'adaptive filter' makes a decent job of removing noise (even if it doesn't help with the background light much).

Anyway, does anyone have some tricks I can use for working with the IRIS gradient remover? There aren't many options to choose from, and I've tried all combinations but it always seems to do this 'inverting' effect rather than actually removing the gradient in a uniform way.

Failing that, what's a better gradient removal tool? I have GIMP and I tried doing a manual background mask with de-speckle, but the result really wasn't to my taste.

Cheers, appreciate the help. I feel that if I can get this sorted, I'll have a solid pic processing flow :)

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The Rolls Royce of tools is Pixinsight's Dynamic Background Extraction. Russ Croman's Ps Plug in Gradient Xterminator is also good and AstroArt, which is a great stacking and calibrating routine, has a decent gradient tool as well.

You can do quite a lot manually in any graphics program offering layers ad curves, too.


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