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A simple way of getting rid of dust donuts using PixInsight
... well, sometimes.
First of all, this method has its limitations. It will work best on images with lots of background where the dust donuts are covering small scale structures. As luck would have it, that describes most of my galaxy images.
The basic premise is that the areas affected by vignetting and dust donuts will be darker than the background which should be of uniform brightness. Thus to make the dust donuts go away, all we need to do is identify those areas and make them as bright as the background. This is easily achieved using MultiscaleMedianTransform and a simple PixelMath formula.
The basic steps are:
1. Duplicate your image and rename it to "LS"
2. Apply MultiscaleMedianTransform to the "LS" image, using 7 layers and disabling them all except the "R" layer
3. Use PixelMath, apply the following formula to the original image: $T+(iif(LS < median(LS), median(LS)-LS, 0))
I've attached a few screenshots of the process.
As stated, this procedure has its limitations, but where it can be used it's easy and relatively quick.
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