Noise reduction technique

[Carole]

Roberto Colombari shared this method on Astrobin, and I tried it today.  To say I am impressed is an understatement.  It does use photoshop.

You basically produce a starless version of the image and then blur it slightly.  Then paste it back over the original blend mode lighten.

This is an experiment I did today with just 1 hours worth of Ha data. 
Top image is normal processing.
Lower image is the same processed image but with the noise reduction technique applied to it.

Will now have to go back through all my images and denoise them.

Link to larger version:
https://www.astrobin.com/full/ktjxkh/0/?nc=user

[Roberto]

Yes, that method produces eye pleasing images but you do lose detail in the nebula that is just making it about noise levels.  The best method to reduce noise is to capture more data! (Not always possible though).

[Carole]

You can always do a composite as it's mainly the areas without nebula that shows the noise.

Carole

[Roberto]

Yes, there's a technique in PixInsight that does this in one go:  you create a mask of your image by stretching and compressing levels to make the noise reduction heavier in darker areas and softer in areas with high signal.  Then use multi-scale linear median transformations with higher blurring for smaller pixel scales (through wavelets).  It sounds more complicated than it is as it takes a couple of clicks.  This is done with the image still linear so that noise does not get stretched.

Roberto

[Carole]

That sounds good, however I don't use Pixinsight, so good to have a method that works in Photoshop.

Carole