Originally Posted by gwgill
It could be that the calibration curves are raising the black level:
From my own testing, using collink -a to include a calibration file raises the black level rather significantly even when using -Ib with a linear VideoLUT. While using collink without -a and calibrated VideoLUT potentially doesn't raise black level at all. Playing around with CIECAM02, always results in a non-zero and occasionally significantly elevated black level depending on the source parameters.
I'd suspect this may be because you are not taking into account the effect which madVR dithering and expanding levels from 16-235 + WTW & BTB -> 0-255 has on a 3DLUT outputting a non-zero black and/or BTB information, since nothing gets clipped. In many ways it'd be nice to have an option for the 3DLUT to always map video range Y<=16 Black -> R0-G0-B0, and never have black output values greater than R1-G1-B1 when dithered by madVR with whatever the 3DLUT outputs from video range Y=17.
Originally Posted by N3W813
What is the difference between a, aa, aw, and al?
See collink's documentation
for a decent description of each.
As far as out-of-gamut clipping is concerned, -i al (Absolute L*a*b*) is by far the worse out of all the Absolute intents on my profiles. Both -i a (Absolute Jab
) or -i aw (Absolute Jab
w/ white point scaling) gave good results for an absolute intent. The oddball was -i aa (Absolute appearance Jab
), which clipped very slightly worse than -i a & -i aw, but had an interesting perceptual twist to how it mapped some colors. Personally if I were going to use an Absolute intent, I would probably stick with -i aw.
Overall for the purpose of madVR 3DLUTs, I've been favoring the -i la (Luminance appearance) intent per an earlier recommendation Graeme Gill made to me because of my gamma woes. Ever since I started creating profiles from larger patch sets, I was able to understand why. This is the only colorimetric intent which attempts to maintain the relative luminance between source colors after collink gamma and gamut correction. At least with my profiles (gamut smaller than Rec709), the nearest-match approach of other colorimetric intents all result in random small to large gamma shifts to colors outside the neutral-axis, without any apparent relationship within a given scene. Overall I don't see much use of -i r (Relative colorimetric) when -i la is available.
I've never really liked -i p (Perceptual) -i ms (Saturation) -i s (Enhanced Saturation) very much, because they are non-colorimetric intents. Perceptual has the best tone smoothness out of all the intents, but otherwise it desaturates colors to match hue. Both of the saturation intents oversaturate colors, making them even more useless than the normal perceptual intent in my subjective view.
tl;dr In my subjective opinion
: la > aw > a > ir > aa > p > al > ms > s