MLT leaving holes + spots in image?

[fnord123]

I am trying to reduce the noise on a linear OSC image.  MLT seems to provide most of the controls I want, but I notice that it seems to leave behind a few pixels that look like holes and others that look like hotspots - e.g. see the attached PNG file, showing a STF stretched post-MLT portion of the image.  I've also attached the pre-MLT .xisf of the same area in case that helps. I have also attached a screenshot of the MLT parameters I am using.

Also, I think there is too much smoothing of the nebula area, and a bit too little in the background areas of stars, but haven't been able to do better than this compromise, even with using linear masking. If anyone has general suggestions on using MLT better here that would be appreciated as well.

Any suggestions to prevent these holes/spots from appearing in MLT, or how to remove them afterwards, would be much appreciated!

[Juan Conejero]

Those spots are outlier pixels, from the point of view of MLT. You can either use MultiscaleMedianTransform for noise reduction, or apply it after MLT just to remove these outliers. Apply noise reduction to the first layer with a large adaptive parameter; say 5-7 MAD units, and leave the rest with default values as a start. This should fix most of these spots without causing any damage to the image. No mask should be necessary, but you can enable it also if you wish.

I would try also with MMT directly for noise reduction. The adaptive parameter is very effective to prevent outliers.