Hi,

At high iso darktable gives for both the wavelet solution (spikes) as
the non-local means (patches) solution ugly strutured noise output for
my NEX_C3. I noticed also some ugly colorshifts in deep shadows going
partially green or purple. However having a look at the denoisified
results of Lightroom output for my NEX-C3 I noticed the typical spikes
from the wavelet output as well as much more randomized noise. I
succesfully combined the wavelet and non-local means denoising
profiles (3 instances) to get a much nicer result very similar in
quality to Lightroom. Lightroom however seems to keep slightly more
structure, I assume they have an adaptive coupling between my multiple
instances.

Here is my approach (note the order of instances matters) for the
denoising profiles

instance 0: wavelet, 100%, strength 1 on the color.
instance 1: wavelet, 50%, strength 1 on the lightness.
instance 2: non-local means, 50%, strength 1 on the lightness.

the non-local means is an adaptive filtering and hence works best as
the last filter. Some documentation on the darktable manual of this
would perhaps safe others the time and effort. I can supply darktable
exported jpegs of before and after per email. Some color blotches
remain, which I usually filter out with the bilateral filter on the
color. I suspect the denoising profile for the NEX-C3 can be made more
accurate to solve this and the odd color shifts in the shadows. Though
I might suspect that there are processing differences between
different white balances. The out of camera jpegs seem to suffer none
of this so I expect this to be possible.

Best,

Gert
-- 
Panta Rhei -- Life is a dance

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