Re: Of black point compensation (short version -:))
Re: Of black point compensation (short version -:))
- Subject: Re: Of black point compensation (short version -:))
- From: lasse seppala <email@hidden>
- Date: Sat, 7 Jul 2001 20:57:37 +0300
lasse seppala wrote:
For softproofing
you should use the rendering intent (perceptual<>relativ) you are
going to use for actual separating.
Henrik Holmegaard wrote:
This would be a bug and not a feature. In the step from source RGB /
Lab to simulation / output space, your choice is perceptual or
relative colorimetric with relative black point (the lord forbid you
do it with absolute). No you have the colors that will print. Then in
the step from simulation / output space to monitor and printer proof
space your application software must *NOT* allow any color
displacement.
The bug in application software except Linocolor 6, Newcolor and
Pshop 6 is that the same intent is used in the first step as in the
second. If you choose Perceptual, you first gamut map into the
simulation / output CMYK space and then try to decompress the gamut
mapping going into the destination / proof space. The print will be
OK but the soft proof will be all over the place. If you choose
Relative Colorimetric with relative black point going into the
simulation / output CMYK space your shadows will not be rendered as
well as with perceptual, but at least they won't be massively
clipped, and your software will not give you the option to convert
into the monitor space, if it works at all. If it does, you're
entitled to ask for your money back -:).
... and your software will not give you the option to convert with
perceptual into the monitor or printer proof space here either, if it
works at all.
If you ask tech support its always a feature...But also in my opinion
it is a feature, because if I have understood PS6 philosophy, monitor
profile is working (suppose relatively) on top of internal PS-lab
showing what is asked.
So if I ask PS6 to show me how a separation of RGB_xx would look
like in Press_yy, I go to View/ProofSetup/Custom and take the
Press_yy-profile. With the intent I select how the resulting
separation would look like as separated with relative or perceptual
intent (I suppose this is not affecting cie/monitor, which should be
relative on top of everything). With Paper white (and black checked)
you have absolute-cmyk-simulation (with BPC) on your monitor. With
only Black ink checked you get relative-cmyk-simulation with BPC on
monitor.
One thing (important) more. You must have set perceptual/actual
press pofile in color settings for this kind of softproofing to work
correctly. If it is set relative in Color settings, screen proofs are
identical (relative) with both intents in proof settings. It is also
best bet to have it perceptual (as discussed earlier) to get safer
separations by somebody pressing CMYK-tab without checking first what
is happening. The best way to separate is always to use
convert-to-profile -dialog (you can check surely the settings) and to
have BPC on (unless you want deeeeep shadows beyond the paper
facilities) if you use relative conversion.
As I described in my original post, it is easy to test simulation by
making two different separations (rel/perc) and softproofing them
(preserve color numbers checked) manually. If you have same
checkboxes checked (White/Black ink) as with RGB_CMYK -simulations,
the relative separation (cmyk) looks identical to rel-rgb-cmyk
-simulation and the perceptual-cmyk looks identical to perc-rgb-cmyk
-simulation. So if this is a bug, I find it useful.
I would like to here some comments from Adobe (or somebody knowing
PS6 under the hood well) how the monitor profile is actually working
in different situations.
These experiments above are self-found, and somebody may have
different aspects. But if there is no different opinions, there is
also no conversation.
Regards
lasse seppala