[argyllcms] Re: Total Ink Limit (aka TAC)

Hi Martin,

Graeme wrote:
     The behavior of a CMYK device near black is not usually simple. In general      there are multiple overlapping, discontinuous regions. For a given target color      (say L*a*b* = 0,0,0) it does not follow automatically that the closest color      will use the maximum possible ink. Some inksets have non-monotonic behavior      near black (ie., often adding yellow makes things lighter for some pigmented inks). 

True. The darkest point in this profile is not on the neutral curve.


Any suggestions on how to find the true TAC?
I can't get those numbers at all. Going from L*a*b* = 0,0,0 to CMYK (rel.col.) I get: 
0.874157 0.770432 0.600203 1.000000 (ArgyllCMS)
87 77 60 100 (Photoshop CS2, Adobe (ACE))
87.4189 77.0321 60.0153 99.9969 (LittleCMS, icctrans.dll for Matlab)
This is what what the tools I have say as well. They try to pick a nearly neutral black, which is about L: 10,08 a:0,25 b:0,08 with a deltaE of 10,1. (I used your original profile)
ColorPicker (part of the ProfileMaker package) has the ability to minimize the deltaE 
and chooses C:100 M:97,0 Y:61,1 K:100.
This results in L:9,46 a:1,28 b:-0,14 and has a deltaE of 9,5.
The TAC of this colour is 358,1%.

Rolf Gierling

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