I would observe caution when using those meters / the vocabulary. The perceived color depends so much on the surroundings that absolute measurements from single points can’t possible cover that.
Here’s a terrific demonstration:
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Thanks for the tip Priort
Thanks for the analysis. I hope the picture can be useful in improving the feature. As I said, the smooth preset is already very good, but it would be even better if there was a systematic way (or at least some guidelines) of tuning the primaries according to the curve parameters. FWIW, in my code I’m following a different approach to the picture formation, but the simplicity of per channel in a custom working space is really appealing, so I’m looking forward to future refinements of the idea/implementation! 
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Thanks for your work, it works great!
I tried it on a few of my pictures that I’ve never managed to look like how I perceived the scene. Left (filmic) has never felt right — the globe is supposed to emit a strong yellow light, but it looks salmon colored. The right picture, using the sigmoid smooth preset, recovers the atmosphere of the room far better.
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But adjust the hand to get the right skin tone and I bet it would be red or more red. I have found it to be surprising how often targeting skin tones and setting them results in the whole photo being corrected from some weird color casts… I am no expert but often when I get a tricky skin color I have used the lab tone curve to tweak the skin tones using the guides offered in DT to bring up the average caucasian tones… Your point is well taken. Every photo is its own challenge
Edit: Just for fun…downloading this image with “no color” and actually looking at it… its not white balanced…if you simple white balance and then you can further tweak things using the hand skin tone using the DT reference as a guide… and then finally CB RGB for set the black as its not right…you end up here… with red for sure…
WB it…on coke letters
Then skin tone and overall tone tweak
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Hello, I left a lights and smoke playraw to everyone who likes to test the primaries for Sigmoid.
Thanks @flannelhead !!
For sure! It has been already. I think it helped already to make it very clear that the skew parameter has a drastic influence on the output, and that with portraits (or probably most kinds of images) it is not advisable to push it very high to positive values. I think this is true of sigmoid’s per-channel mode in general.
I think in this particular case this wouldn’t have helped much, since the more red areas were in such position that with the chosen curve, they only ever get some increased purity but none of the desired shift toward yellow. With that particular curve, I don’t think any settings of the primaries would have remedied this, like you also found out.
Would be really interesting to learn more about this. Where should I start looking?
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Yes, sure it was not white balanced. The point I tried to make was that in the original, the can is clearly perceived as red, but no color picker would be able to tell you that.
This kind of a thing will happen on smaller scale in pretty much every picture, so it’s always best to rely on one’s eyes for judgement.
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Well, it depends… I prefer to keep the dynamic range compression separated from the contrast recovery and “path to white”, so these are in two different places. Assuming you are interested in the latter, it’s essentially here. In a nutshell:
- save the original hue in jzazbz
- apply gamut compression for the output profile, using the aces method
- apply a per-channel tone curve (in the working profile)
- restore the original hue in jzazbz
- apply some handtuned hue shifts and highlights desaturation. This is the part I’d like to improve ideally
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I wonder do our eyes WB or do we just know the can is red and have a strong perceptual bias, or both 
It’s both - interpreting wavelength of light is done just in the brain.
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Would a moderator like to split out the discussion starting from Introducing "primaries" feature for sigmoid - #44 by Till80? This is an important discussion and deserves a thread of its own. I’ll also chime in later, right now busy IRL…
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Yes, done.
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I recently had a photo assignment where my task was to document one union campaign photographically. The union members were all wearing different safety vests.
While editing photos, I realized that the orange vests were very difficult to process with sigmiod options alone.
Here is an example. At first I had to underexpose the shots a lot because orange vests threatened to break the gamut limit:
When increasing the exposure with exposure module and increasing the contrast in sigmoid, the orange vest went right over the gamut. Note that the green-yellow vest, for example, remained within the gamut:
Increasing the attenuation of the red primary did help but with very strong desaturation as a result:
One option to counteract this was to reduce the brightness of the highlights, but the contrasts in this area were greatly reduced as a result:
The best solution was to reduce the brightness of the red channel with the help of an additional instance of the color calibration module:
The question that arises for me is, would it make sense to have the reduction of the brightness of the individual primary colors in addition to attenuation and rotation for such cases, or should the brightness - as in this example - be regulated with a color calibration module?
What do you think @flannelhead ?
Here is the raw file for testing purposes:
Creative Commons, By-Attribution, Share-Alike
_DSC0602.NEF (90,5 MB)
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Funny with tricky oranges I used to use the two skin tone patches on the CLUT module and or click on the orange patch to sample and then edit it there… worked surprisingly well … Might try to mess with primaries and other … I feel like personally I will be using the rgb primaries with filmic more that sigmoid… I am just better at using filmic to get the looks I want esp with v5… so pairing that with rgb primaries where you can boost or attenuate should provide as much control… Other than helping sigmoid out if you use it is there any real advantage to using it and the primaries with in that module over using rgb primaries with filmic??
Using the workflow recommended by @flannelhead , with the sRGB-optimised settings, and color balance rgb after sigmoid:
_DSC0602.NEF.xmp (11.6 KB)
One could increase perceptual saturation for highlights even more. With 50%:
And at 75%:
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This is one of the cases which shows that we would really need a sensible “gamut mapping” right before the output profile conversion. This would serve as a guard rail to handle these situations gracefully.
As a workaround, you might want to have a look at the suggested alternative settings in the initial post. The idea is that when sRGB primaries are used for the working space inside the sigmoid, when applying the per-channel curves, you won’t have values outside the sRGB footprint as long as you keep the recover purity setting at bay.
Behind the scenes, sigmoid first pulls all the input data inside the sRGB footprint before applying the attenuation, so nothing is clipped at that stage either.
Here’s my attempt with those guidelines. Sidecar embedded.
It seems @kofa was faster than me 
I think this is out of scope as it doesn’t naturally fit within the process that is implemented by sigmoid.
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