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

Martin Weberg wrote:


profile -v -qm -kp 0 .17 .9 1 .53 -l350 -L100 -SAdobeRGB1998.icc -cmt -dpp 
FOGRA39L.ti3



Quick calc -> 87+77+60+100=324%?
(icclu ... -ip ... -> 322%)

Shouldn't it be more close to 350% if -l350 specified?


A few things:

    The total ink limit is a maximum, not a target.

    The ink limit is imposed at the grid vertices, and the
    linear interpolation within grid cells and output curve lookups
    may give outputs that sum over the limit.

    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).

Having said that, I don't get quite the same results as you:

icclu -fb -ir FOGRA39L.icm
0 0 0 -> 1.000000 0.856338 0.575142 1.000000

with the sum 3.43148, but that's with my development code, which may
be a little different to the current release. Your result doesn't seem
unreasonable.

Graeme Gill.

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