ART
exposure compensation -1EV
highlight reconstruction off
tone curve film-like
local contrast
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Can you recommend settings for dummies like me? I donāt work in a lab, but in our living room; sometimes, I develop my photos at night, beside a warm white desk light; sometimes during the day, by the window, and outside it may be sunny, or it may be raining. Therefore, simply trusting my eyes may not lead to consistent results.
- Iād think that at least the āclipping indicationā should be useful. The defaults are, I think, āfull gamutā, -12.69 EV (8-bit sRGB), 99.99%.
- For the histogram (as I never print and just post online), should sRGB be good choice?
- Or should it be one of Rec2020 PQ and HLG? And which one? They are not even remotely similar:
Based on those screenshots, will my highlights be clipped in output? Will my blacks be grey, or have large black spots? Do I make full use of sRGB, which looks like this (not too far off from HLG Rec2020):
- Should I just ignore gamut checking?
ā Or only use it when I adjust OOG colours in CAT? - Which setting (softproof or histogram) does gamut checking use? (Update: experimenting shows it uses softproof.)
- Does the clipping indicator use the same one? (It seems to use a weird combination of display + histogram, see the different sets of pixels highlighted by the clipping indicator.)
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You seem to be hitting this issue: Choice of display profile affects histogram, color picker values and overexposure indicators Ā· Issue #3271 Ā· darktable-org/darktable Ā· GitHub
i.e. the display profile affects the clipping indications and histogram even if it shouldnāt.
Iāve found the ISO 12646 colour assessment conditions (the lightbulb icon in the same toolbar as the clipping and softproofing toggles) pretty useful in this kind of a situation for better judging the middle grey exposure and the highlights. Also I usually adjust the (laptop) display brightness to match the environment.
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Thnaks for the explanation, Iāve realized only today that is possible to brighten the image with the level tool before the profile conversion and it works too.
DSC_7355.nef.xmp (9.4 KB)
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But why are you hurting yourself like that ? It does not āworkā, you are merely exploiting a drawback of some algo to desaturate in an uncontrolled way and the profile is designed to work on linear RGB input, while you are now feeding it non-linear RGB, so itās basically wrong.
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People at the aces central forum have developed a fast rgb gamut compression https://community.acescentral.com/t/wrapping-up-the-architecture-vwg/3433
Really great stuff 
Iāve implemented a semplified version for gāmic.
There are only two parameters, gamut that is the strength of compression and threshold, under this value the distance (āsaturationā) is untouched
the steps are
1)found achromatic , same as Value in HSV
2)found distance, similar to Saturation in HSV
3)apply tonemapping on ādistanceā
4)come back to rgb
Here itās explained very well https://paper.dropbox.com/doc/ACES-Gamut-Mapping-Architecture-VWG-Technical-Documentation-Deliverable-tZHiuOCj0RdYw8PPkrTam
This is the the Gāmic code, however it works in Photoflow but not in Gimp 
-fill \
gamut=1.3;\
thr=0.79;\
thr1=(thr*(1+thr/(gamut*gamut)))/(1+thr);\
i=i/255;\
ach=(max(i0,i1,i2))/255;\
distance=(ach-i)/ach;\
compressed_distance=(distance* (1+distance/(gamut*gamut)))/(1+distance);\
compressed_distance=((((compressed_distance-thr1)/(1-thr1))*(1-thr))+thr);\
compressed_distance=if(distance<thr,distance,compressed_distance);\
i=ach-(compressed_distance*ach);\
i=i*255;
DSC_7355.pfi (22.7 KB)
original
simplified rgb gamut compression
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How is blue degrading to magenta āgreatā ?
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A lot, at least with the idea behind it we could:
a) use the formula sat= (max - min)/max as a mask for the detection of oog colors in the current rgb working space, only values higher than 1 are outside of the gamut.
We could even clamp this mask to 0-1 and it would be useful for less global desaturation where itās not needed.
b)restore luminance and hue from the original not desaturated image
EDIT:
Itās easy to keep the ārgb hueā locked, just use the same strategy used in the filmlike curve in Rawtherapee and Lightroom.
Basically apply the tonemapping function on the max channel, in this special case the minimum channel is always normalized to 0 and linearly interpolate the middle value with the formula : middle= (middle / oldmax) * newmax
In this way the new middle value keep the same relative distance from the max and min channels (same hue).
Iām not sure you got the answer here and not sure I could advise you better than you already know but you might find this interestingā¦esp the last few comments near the end which are more recentā¦ as you can see the users are not the only ones that get confused by these thingsā¦ Choice of display profile affects histogram, color picker values and overexposure indicators Ā· Issue #3271 Ā· darktable-org/darktable Ā· GitHub
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What really bother me isnāt the hue shift but the flat and washed out look, using the power norm instead of the max rgb helps preserving the āluminanceā.
Gamut compression using the power norm
With rgb curve and raised saturation
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