Call to advice for fighting color noise

@Andrius Tried your method today and the results are amazing, even though I had no dedicated camera profile and used generic poissonian preset instead. Excuse the hastily applied mask to focus on the sky, but the results speak for themself!!!

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@mosaster I am glad it worked for you.
I wish I could take a credit for this but I just copied somebody’s method.
I guess darktable devs have done a great job :slight_smile:

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To smoothen out, I like to put an instance on top of the stack using average blending, which just gives it the final touch.

…aaaand of course, YMMV. :slight_smile:

I saved the three instances as a darktable style and uploaded it here:
https://redmine.darktable.org/attachments/download/3411/denoise%20profiled%20stack.dtstyle

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Wow, that worked great for me // saved them as presets // used them on other images that I was having trouble with and so far, really good results.

Thanks for the NR presets. I’d modify them according to what houz suggests in this text:
“For profiled denoising better use ‘HSV color’ instead of ‘color’ and ‘HSV lightness’ instead of ‘lightness’”.

Thank you for the comment.
I followed the link and finally got here:
http://darktable.org/usermanual/ch03s02s06.html.php

I am wondering what “clamping” is

@Andrius See https://en.wikipedia.org/wiki/Clamping_(graphics)

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Thank you afre

This is awesome!
My only real issue with DT was terrible noise reduction. Turns out it was just me being ignorant and didn’t understand the tool.
Thank god for that lol, I can now ditch Lightroom with confidence.

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Some time ago I profiled my Fujifilm X-Pro 2 in accordance with the dt procedure and was surprised at the good (excellent) results obtained.
When I use either the ‘2-step’ or the ‘3-step’ (mentioned above ) option I see absolutely no difference from that produced from my single step usage.
Possibly it is my camera or the individual profiling … but I do like my simple results.

Probably I should have also mentioned … the X-Pro 2 is already well corrected for noise at ISO 800 by Fujifilm. Noise at that setting is not so different from the base200 setting. I do use that ISO 800 setting for 95% of all my imagery.

A sidenote here : there is no such thing as chroma or luma or colour noise. It’s just noise. How it looks, once it enters our perceptual system, doesn’t change what it is : garbled data on RGB channels.

Similarly, the denoise profile module in darktable doesn’t know any colour or luminance since it operates in camera RGB. That camera RGB has nothing to do with our perceptual system, and will need to meet a colour profile to be remapped to XYZ and then to well-behaved RGB spaces, where chrominance and luminance have a meaning.

Blending the denoise profile in lightness or colour is therefore a theoritical mistake since these are Lab modes. HSV lightness or colour are equally wrong since the conversion RGB -> HSV assumes well-behaved RGB spaces, while the camera RGB can be absolutely whatever.

The last changes in denoise profile module (in future darktable 3.0) should make these blending modes irrelevant, since they essentially hide misbehaviours of the denoising algo.

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@mosaster Knock yourself out…all the info you should likely need here… https://tomassobekphotography.co.nz/articles/reducing-noise-in-Darktable.php

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This is an old thread and probably older than tje reference.
Nevertheless this Tomas’s website is quite something!

Thank you very much Todd for pointing to it!

I just wanted to say I strongly agree with Aurélien on this point :slight_smile:

Y’know, I think I’ve found that particular post of @aurelienpierre’s to be one of the more insightful things I’ve read recently. I think we tend to overuse the downstream manifestations of artifacts in our images to attempt correction, and we become vexed when those corrections don’t always bend things to our will. Using temp/tint for whitebalance manipulation in post-processing is another example, IMHO…

Personally, I de-noise the individual RGGB chanels before de-Bayering. Removing noise is easier before it has spread to other pixels. For example, a 1:1 crop of a noisy (ISO 256000) image:

With de-noising of the RGGB channels:

The de-noising was simple: ensure every pixel is within the local minimum and maximum of a small blur.

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I do want to explore denoising before demosaicing but

1 I am still a newbie at denoising, compared to many people here.

2 I know not of an app that does good debayering post custom operations. Currently, I rely on apps to do the raw processing and then I export an unbounded floating TIF.

  1. I’m also a newbie at de-noising.

  2. Any raw-reader can be used. I use dcraw to extract the RGGB channels, then ImageMagick to do whatever processing I want, then exiftool to build a mosaiced DNG file that any raw-reader can read. This isn’t interactive, but doesn’t need to be for my purposes. When I have a couple of hundred photos that need the same denoising, the computer can get on with it while I sleep.