Re: Preserving the black channel
Re: Preserving the black channel
- Subject: Re: Preserving the black channel
- From: Henrik Holmegaard <email@hidden>
- Date: Sun, 14 Apr 2002 17:16:47 +0100
email@hidden (Lee Blevins) wrote:
0,0,0,100 (cmyk) would not be L 100, a0, b0 from what I understand of
that color model.
The point is simply that Lab is the PCS and RGB / CMYK are device
colors. If you define black in the PCS then that object isn't
reproducible without mapping PCS black into the physical black of
whatever device. Hence for Lab objects the concept is always that the
user is asking for the object to be color managed into composite
black.
PostScript Level 1 has a concept of RGB and CMYK as device spaces and
of a generic RGB to CMYK conversion based on black replacement rather
than on color. I guess all the switches in the color servers and ICC
frontend for RIPs are passing R0 G0 B0 through a Level 1 rotation
into K 100 and leaving K 100 alone as device color. But they can't do
that with Lab L0 a0 b0.
As others have stated we should turn off the profiling and try to
linearize the output device.
This is the technique we've used for decades in graphic arts.
Unfortunately, the hues of the colorants make this not work since they
don't match our "standard" process colors.
Not just for the colors, but for the black replacement, too. Any CMYK
- Lab - CMYK conversion includes a reseparation and every printing
process should have its own black replacement and ink limit. This is
the good thing about digital contone proofing: The color is addressed
and the reseparation is addressed.
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