Robert Krawitz schrieb am 08.03.2018 um 03:52:
On Wed, 7 Mar 2018 20:36:14 +0100, Matej Martinovic wrote:
Hey,

denoising in darktable is somewhat tricky:

Use the *denoise (profiled)*, set it to "wavelet" and set blend mode to "color". This 
eliminates the awful color noise. Use a *second instance* of denoise (profiled), set it to non-local means 
and choose blend mode "lightness". With that second instance i'll usually reduce the strength or 
opacity to my liking to keep some detail.

You can set some presets and have them apply the correct denoising 
automatically.

This info is also available in the manual 
https://www.darktable.org/usermanual/en/correction_group.html, under 3.4.4.3. 
Denoise – profiled -> mode.
I've tried this also a number of times, and also find the NR from
Darktable unsatisfactory compared to RawTherapee.  I'm using a
7DnmkII, typically at ISO 6400-8000.  I've posted a number of examples
here:
https://rlk.smugmug.com/Photography/DarktableRawTherapee/i-pZbDfRH

It's unfortunate; there are other reasons I'd prefer to use Darktable,
but when I need significant noise reduction, the artifacts I get are
simply not satisfactory.

On 2018-03-07 19:59, darkta...@911networks.com wrote:
DT 2.4.1

I'm having problems with the denoising:
Canon 7DMkII and Canon 70-200L IS f/4 ISO1250

Darktable:
* before denoise: https://i.imgur.com/k9Njy70.png
* denoise profiled: https://i.imgur.com/Unw2i8O.png and it's very
    blotchy
* equalizer denoise: https://i.imgur.com/8E1CzHt.png (w/o the
    denoise profiled). Less blotchy than profiled but not good either.

I have also tried Rawtherapee
* after noise reduction: https://i.imgur.com/Js5ZGfd.png and it's
    excellent

What can I do to improve the image?
I found some improvement recently on my D500 by playing with https://www.darktable.org/usermanual/en/modules.html#demosaic demosaicing before doing anything else. I have adjusted the settings in such a way that the structure of the noise appears as "even" as possible. This makes the artifacts less conspicuous after denoising.
Worth a try I guess.

--

regards
Bernhard

https://www.bilddateien.de

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