Thanks for clarifying. I noticed only that the other colours were very subtly shifted to be slightly lighter overall, not different in the sense of changing to another hue or colourfulness perceptually speaking. Anders says this makes for a more robust general-use profile with cameras that are overly blue-sensitive and it only sacrifices colourimetric accuracy very slightly in more common, less saturated colours for significantly better handling of the extremely highly saturated colours. He cautions to expect that a profile which handles extreme colours well (depends on what each of us mean by ‘well’) might not be so accurate for less saturated colours and contrariwise. I have a set of profiles for my Sony with the Y limit at a less negative value and another where the Y is allowed to be as negative as the optimizer thinks it should be for a more colourimetrically accurate result.
That’s an interesting idea. I think that a company like Lensrentals, actually I can really only think of them in this context, is ideally positioned to offer SSF data. They can measure multiple copies of the same camera, average the variation if they find any (I’m under the impression that it is very minimal), provide pure camera or camera+lens SSF combinations of all sorts to us because of the amount of inventory they have. I would be happier to pay for that data rather than have to travel somewhere in person with my camera or ship it to someone to have it measured and Lensrentals has established themselves as some of the best and most trustworthy in the world for optical measurements.
I was doing a bit of Googling regarding IT8 targets (thinking along the same lines as @ggbutcher …) and came here.
One thing is: It appears that you’re comparing IT8 “full” profile vs. CC24 matrix - what about dcamprof vs dcamprof with the two targets?
I’m probably going to buy an IT8 target anyway… And I’m wondering if there might be some good use cases for the transmissive IT8 charts (put a diffuser behind a transmissive chart and shoot through it to eliminate the glare concern?)
All three images in the OP are rendered with dcamprof profiles. Look in the colorspace parameters, bottom-left, and the profile filenames confirm it (I had to go look, couldn’t remember… )
DCamProf can make a pure matrix profile (with shaper curves if a transfer function is provided via the -t parameter), and a LUT profile with either camera RGB to XYZ conversion or camera RGB to Lab.
Quoted…
Also quoted…
DCamProf can make an RGB to XYZ or an RGB to Lab LUT, the latter is the default. Currently the XYZ LUT uses the forward matrix directly which means that extreme value handling is not as good as the Lab LUT, so I recommend using the default Lab LUT.
So, in the ICC transform, there are two steps: camera → PCS, then PCS ->destination. If the camera profile converts to Lab, then the destination profile needs a matrix/LUT that converts from Lab. I don’t have any; I use Elle Stone’s ‘well-behaved’ profiles for most of my destinations, and those are all XYZ anchored.
Unless I’m missing something about the process, which is likely…
Not likely , I really just wondered if there there was a technical reason and I had remembered a tid bit that lab was preferred for lut creation…I went to check on the color charts…listed as sold out…
When you stick 2 profiles together to make a colour transform, the CMM* will perform conversions between XYZ and Lab PCS encodings as necessary. So (unless you are writing your own colour management software) you don’t need to worry about it.
Sooo… if I create a camera profile with dcamprof and the lablut parameter, if I use this profile in a transform to, say, Elle Stone’s v4 g22 sRGB profile (which has XYZ round trip matrices), LittleCMS will do camera → Lab, Lab → XYZ, and finally XYZ → sRGB? Never got that from the docs, although my reading was mainly "how does cmsTransform() work?, to do rawproc coding…
I think we do too much slinging of the pixels raw processing, so adding more transforms, especially one that departs, then returns to RGB coordinates, is not appealing…
With more patches, It’ll probably better-inform a LUT profile out of dcamprof; the 24-patch ColorChecker can really only well-inform a matrix profile. Make sure it comes with a .ti3 reference file, or something you can easily massage to that for dcamprof…
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