I’ve been reading about and experimenting with the color calibration module, and I’m having some trouble understanding the color mixer feature.
I was expecting the three color mixing tabs to simply work as interfaces to input coefficients OI in a matrix, where O is the name of the tab (either R, G or B) and I is the name of the slider, which is the multiplied with the input channels to produce the output:
So for example setting everything to zero except for any of the entries in the R tab would produce a red image, and this is true when adaptation is set to none (bypass).
So far, so good. Now, the manual suggests using the color mixer with the CIECAM16 adaptation (i.e. color model?) enabled, even if the CAT tab is not used (in which case the manual suggests setting illuminant to same as pipeline (D50)).
I understand that by changing a different color profile (or color model or …? as is probably obvious I’m not familiar with these concepts) than the pipeline, repeating the same thing as above (everything to zero except one slider in one channel) the resulting image will likely contain a mix of R, G and B due to the mapping back from CIECAM16 at the output of the module.
However, at this point the result puzzles me: while setting only input R in the R tab does produce a mostly red image (with some blue) as I expected, doing the same with G or B produces a perfectly black image. Here are some screenshots with a bit of the image, the histogram and the color calibration settings to illustrate what I mean:
What am I missing?
Also, another question that I suspect might be related: why are the colors in the R and G sliders basically identical (though reversed) and those in B completely different? I expected these sliders to be different in each tab, as they indeed are when the adaptation is set to none (bypass):
I tried to figure this out by reading the documentation of this Darktable module, about CIECAM16, and so on, but I guess that I lack knowledge of some fundamental concepts that are required to understand this. I’ve also seen quite a few similar-sounding questions posted here, but they did not help me in understanding this.
P.S. I’ve posted this question on stackexchange about two months ago (I didn’t know about pixls.us yet), and I’m only reposting it here because nobody was able to answer there and someone suggested I ask it here.