Explanation of SCNR Settings?

[jkmorse]

I am trying to dig deeper into the workings of various PixInsight tools since there is only limited documentation.  Earlier I asked about how to set up the parameters in CosmeticCorrections when using a Master Dark and am still hoping to get some insights there.

Today I want to better understand the SCNR settings.  I have tried reading previous posts and have gleaned some information.  For example, if you have a green tint throughout the image, you should be using the default Average Neutral setting.  I also read that Maximum Neutral should clean a green cast in the background without impacting at least OIII regions and, I am guessing here, brighter regions generally.  The reverse implies that Minimum Neutral should impact the Target but not the background but that is just speculation.  I have also read that SCNR destroys data which is always a concern.

Playing with the tool only takes you so far because you need to have an image in need for a certain type of fixing before you can test all options.  Here's hoping I can get to the next level by getting a quick primer on how this tool works at a nuts and bolts level.

Thanks,

Jim 

[msmythers]

Jim,

One of the things I did to understand more of the effects of SCNR was find a color chart for web page design. I then applied different settings of SCNR to that chart. You can find charts that have upwards of 2000 separate color samples in one chart. It's interesting to see what changes.

As far as does it destroy data, it can. The question is if what you are trying to remove is valid data? That's how I see it. Also I never use SCNR without a mask.



Mike

[topboxman]

Mike,

What kind of mask do you use for SCNR?

Thanks,
Peter

[msmythers]

Peter,

What ever type is required for the image and situation. If stars are greenish then a star mask. If the background has some green or another color that's not right then I might use a range mask or luminescence mask combined with a star mask and target just the background. I shoot in heavy light pollution without filters so strange colors can sometimes be a problem. SCNR works well for my images.


Mike

[topboxman]

Thanks Mike.

I also live in high light pollution area and image without LP filters and have used PI for a while. I don't like LP filters because it affects color balance so I don't use it and rely on PI taking care of LP gradients and has worked pretty well. I have begun to notice purplish backgrounds and not realized it may be been caused by SCNR. There was another thread about SCNR and color calibration and I got interested in trying to improve my images.

My images always show greenish cast and usually on DSOs especially galaxies so I can see that can be difficult to decide on the proper mask for SCNR.

Thanks,
Peter