I don’t think so.
Certain norms (e.g. luminance Y) help, as does preserve chrominance = no.
I just had a quick try, and what - I think - already has been said in the topic:
Set preserve chrominance to ‘no’ and things appear right almost directly.
Whichever preserve-mode I pick, filmic v5 doesn’t do better (except ‘no’).
Luminance-Y comes close, but the trousers of the sailors get a bit blue, while they stay white / warmer with just set to ‘no’.
In the top-right between the leaves is also a bit of overexposed sky. When set to v6-‘no’ I don’t have to do anything to it, not even filmic-reconstruction. In other modes it’s magenta and I have to grab the highlight-reconstruct module (didn’t try filmic’s to be honest).
preserve-mode set to ‘no’ does make the highlights really ‘pop out’. The people in the middle-right with white shirts for example, they look really bright (blown out?). The captain with the full beard right of the tail of the fish, his beard also seems rather blown out. But changing preserve-modes doesn’t really bring it back. Toying around with the tone equalizer, you can bring the highlights down and the shadows up to lower the contrast of the scene before hitting filmic, but that might not be the look you’re after.
(although dragging tone-equalizer before exposure (so under it) and picking one of the ‘soft’ compression presets is not that bad actually).
‘max rgb’ really tries very hard to get any kind of color out of it. And if your highlights are really white (like the trousers here) it just turns them into some color that’s not really correct.
It’s not an easy one, I give you that. Makes me want to go back to some pictures and try some other preserve-modes :).
I posted a filmic v5 version (the 1st image, in fact), and I think it does a fine job out of the box. Try opening these in tabs, and switch between them:
ah, my dropdown boxes bug out with recent gtk versions, so once I click something it doesn’t always ‘stick’…
using the scroll wheel to go through modes is more reliable… filmic v5 with preserve-mode set to ‘no’ and filmic v6 (with no) are very very close, and both work well.
@flannelhead can you explain - to someone not knee-deep into color maths - why ‘preserve chrominance’ set to no is still hue preserving?
Am I correct in explaining it as 'it does not try to keep saturation, or ‘how much color’, but it does keep ‘which color’, by not causing color shifts?
So the trousers have some blue in them somewhere, but with preserve-chrominance to ‘no’ they are just so high in luminance that they appear white?
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Chrominance is the colour correlate of the norm. If the colour of the source is incorrect to begin with or one modifies one without the other, then one would end up with funky colours.
Sorry, English is not my mother tongue.
Webster’s defines correlate (noun) as
1: either of two things so related that one directly implies or is complementary to the other (such as husband and wife)
//brain size as a correlate of intelligence
2: a phenomenon that accompanies another phenomenon, is usually parallel to it, and is related in some way to it
//… precise electrical correlates of conscious thinking in the human brain …
darktable’s docs only mention chrominance to note that it’s not the same as chroma:
chroma is not short for chrominance, which is the color part of a video signal (the Cb and Cr channels in YCbCr, for example).
Those two don’t help me understand what you mean.
I should have just stuck with component. In short, chrominance as it relates to the norm is image divided by norm. I am a very tired: someone please correct me gently if I am misspeaking on the matter. Essentially, chrominance is the direction component of the vector and the norm is the magnitude. If you know what I am talking about, it is easy to understand why a change in direction or magnitude would change everything, especially something as sensitive as colour.
Yes, there is that. The CIE definition is a value that can be calculated and used as an intermediary for other calculations. @jdc is the gentleman to ask. Just don’t do it in this thread.
There is a nice video there taken from the perspective of painter in the digital realm…I think he defined it as chroma / max chroma possible for a given hue… outside the scope of my knowledge really but makes sense I think
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Glad you asked. The ”no” mode first applies the filmic curve to each channel individually. This causes a desaturation in the highlights and a hue shift. However v6 then restores the original hue (”which color”) but keeps the new chroma (i.e. ”how much color”). This is followed by gamut mapping to decrease the chroma in order to fit within the output color space. So I think your explanation is pretty accurate.
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If I remember correctly, there’s also an effect on the shadows, where the individually applied curves would cause a hue shift + oversaturation; and filmic v6 counters both (in contrast with highlights, where the (lowering) effect on saturation is retained).
Actually the shadows don’t get any special treatment there, so filmic v6 with the no chromaticity preservation mode gets that resaturation of shadows. However, that’s followed by gamut mapping so there should be no hue shifts in the shadows.
Thank you! And for comparison, how does v5 behave?
Has the behaviour described here changed?
- for the non-chrominance preserving method (independent RGB channels), we still enforce hue to be passed along from input to output. We still keep the desaturing behaviour in highlights but we set the original chroma in shadows to avoid resaturating.
Actually yes, you may be right 
I forgot there’s also a function that changes the chroma a bit before final gamut mapping. Too tired to read the code now though, getting back to this tomorrow
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