János, Tóth F. wrote:
But it sounds much easier to set up those three ambient view condition presets with fixed curve parameters.
You could probably approximate what CIECAM02 does using a standard power-curve-with-straight-segment, but to do that you'd have to sample the CIECAM02 curve and then use a fitting algorithm to derive the parameters. Is that somehow easier ? Of course I just used the whole CIECAM02 algorithm because I had it available (and I think it is in lcms too), but you could tease out the luminance processing and figure out a simplified equation, but it won't be a power-curve-with-straight-segment.
Otherwise, I can't really believe in CIECAM02 here because it's much younger than Rec709. (There is no way that Rec709 has anything to do with CIECAM02. At least officially...)
They are completely different things. Rec709 is just a standardisation of an video encoding. CIECAM02 is a human color appearance model, so it's specifically designed to model color appearance, rather than it happening as a side effect, which is what has happened in TV standards.
So, I think: If the "scaled inverse encode curve" is really meant to be used on the end-user side, then there should be a commonly accepted/suggested way for this scaling method. (Which had to be exist long before CIECAM02...)
No there is not. The color appearance transform effects of the mismatch between the TV encoding and actual display response hasn't been widely understood. Presumably the original TV engineers tweaked the encoding curve to give the right looking response on a CRT display, and this winds up corresponding to an encoding gamma of about 2.2. A typical CRT has a gamma of 2.4 or so, giving the studio bright to living room dim appearance adjustment. Read this http://www.poynton.com/notes/PU-PR-IS/Poynton-PU-PR-IS.pdf, and this http://www.poynton.com/notes/color/GammaFQA.html, or better yet, get a copy of Charles Poyntons book: http://www.poynton.com/DVAI/index.html
And another concern of mine that this curve is well defined but otherwise "hard to scale". It wouldn't make me think that I should use it in a scaled form. (Or where are the scaling formulas and/or the suggested curve parameters then...?")
I'm not quite sure what you mean. Graeme Gill.