ACES 2.0 CAM DRT Development

[priikone (Pekka Riikonen)]

I think there is one additional piece, which is that the compression happens along the perceptual hue line, which skews the color to even more cyan in the chromaticity space, making it also appear brighter (that hook in the 2D diagram). @bottosson explained why this happens, which I think is what’s also going on here.

@bottosson

This problem is unfortunately even worse if doing projections along constant hue and lightness lines. The reason is that the faces of the RGB cube end up almost perpendicular to hue and lightness in certain cases. This is most apparent in the transition from blue to cyan. You can clearly see it in this plot. Here in Oklab, but all models matching perception of hue will have this issue, since it is a property of hue perception.

I guess the claim would be that this is perceptually correct, but it sure doesn’t look correct. We get similar looking image with the current DRT with dark blue/cyan transition, but not so extreme, it’s much better.

We can try to improve this by changing the lightness mapping (J projection) in the gamut mapper. But the perceptual hue lines around blue (perceptually accurate or not) will have big impact as well.