Uniform LAB space

[st599]

I have been playing with CIELAB as a color processing space and ham having issues with hue shifts in blue. This is a known issue apparently, Braun, Fairchild et.al. discuss a solution in a paper from 1998 [1]

Do any of the open source libraries implement this hue linearized LAB concept, or do they use the CIE space?

[1]http://rit-mcsl.org/fairchild/PDFs/PRO04.pdf

[heckflosse (Ingo Weyrich)]

ping @jdc.

[Elle (Elle Stone)]

RawTherapee has such code:

Color Choosing Paradox, also Warmer vs Cooler

@Elle For correction Munsell<==>Lab, I don’t use UPlab Profile (I think it’s buggy, but thats not the problem…). I use 195 LUT (I deposited a copyright) for each Munsell reference : Color ,saturation and Luminance (in Munsell notation). I give to the LUT, Luminance Lab, Chroma Lab, and Hue Lab, then I obtain a correction. This system is not perfect (what is perfect ?), but differences are very, very tiny (1 or 2%). The system is very fast, and don’t use much memory (each LUT is very small about…

[jdc (Desmis)]

@Elle @heckflosse Thank you

In addition to the link

There is as much LUT as necessary.

They are distributed according to the luminance, the chroma, and the hue, with a “concentration” all the higher as the Munsell-Lab differences are important.

The largest differences are for Blue-Purple and Red-Yellow and can reach 0.45 radians and 0.3 radians respectively.

For the other colors the differences are lower, often of the order of 0.1 radian, but it is not negligible

LUTs are initialized when Rawtherapee starts, then processing times and memory consumption are low.

Jacques

[st599]

Many thanks all,

I’ll have a good read when back at work.