Light Pollution Tool Problem

Have you tried running a stack without any calibration files to see if the artifacts remain?

I have seen an effect similar to this in the past.  But, as I recollect it occurred only when I used the light correction tool on an image that had already been light pollution corrected.  Basically the effect is called posterisation.

When APP runs the LPC tool it produces a color correction model that attempts to flatten out the color gradients in the source image.  Assuming selection boxes are well placed the tool provides an excellent (but inevitably somewhat imperfect) result.

When the process is repeated, the selection boxes will be placed somewhat differently and the tool will produce a revised color correction model that attempts to flatten out these minor residual variations.  Inevitably however there will still be minor residual color  variations in the darkest areas.

The posterisation problem occurs when APP is asked to display the highly-flattened 32 bit resolution image produced by the LPC tool, highly stretched, on a computer monitor only capable of displaying color at much lower resolution.  The result is the very minor residual color gradients in 32 bit resolution image start to show as steps at the lower resolution of a color image.

So basically I think nothing is really wrong with your image.

Mike

@mestutters thx for your tip, i will look for that