Mottled Background Example

Reggie Jones

Hi.  I'm having trouble solving a problem where I get a mottled background after using noise reduction, specifically after using TGV Denoise.  In this example, I used MLT in the linear state to do some noise reduction which seemed Ok, but then I used TGV Denoise and just couldn't keep the mottling from happening.  I've sent you a Google link with the file to review.  I'm sure I'm probably using TGV Denoise incorrectly as well as MLT and to some extent, Mure Denoise after they changed the script a bit in this latest version of PI (and of course after I reviewed the nice original tutorial on Mure Denoise).  I've watched your TGV Denoise tutorial several times but I don't seem to completely get it right.

I also need a lesson on the different types of noise you can encounter and how to deal with them.

Thanks; Reggie Jones  

BlockHead

The main point to understand, especially when using MLT and TGVDenoise, is that removing small scale noise will make more obvious the large scale variations. This is because the contrast in the background becomes "better" for these variations. 

Without seeing the original data, it is hard to say.

But one thing that often people need to hear- is that there truly is a data quality threshold The noisier the data, the *less* processing you can do to it. There is only one fix for this, better quality data (which could mean more exposures, longer exposures, darker skies, better sensors... etc etc). 

That being said, it all depends. Even if you do all of the processing "perfectly" (best choices, "get it right" to use your words) you still may not have an image quality you think is good enough. But this isn't a processing problem.

-the Blockhead