[argyllcms] Re: Profile generation with perceptual intent with compensation for paper white
- From: Henrik Olsen <henrikolsen@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 21 Sep 2017 15:48:32 +0200
On 21 Sep 2017, at 14.34, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:
Henrik Olsen wrote:
Hi,
That seems to be what I want. Control over how paper white point is being
mapped. I’d
like my (perceptual) profile to neutralize any offset in paper white,
typically blue,
så my colors won’t have a blue cast.
sorry, that makes no sense. By default all the intents except absolute
colorimetric
make the paper perfectly white and neutral. You can easily check this by
feeding
L*a*b* 100,0,0 into a profiles B2A table, and you will get CMYK 0,0,0,0 out.
Can see the wording can be a little tricky. “Perfectly white and neutral” to
you means no ink on paper, it seems. To me neutral means a* and b* is 0. I
print on inkjets with RGB interfaces, by the way.
If I take a paper/profile like their RC Photo Luster with a typical bluish
look with a
Lab b around -9 the difference is clear compared to other profiles for
similar bluish
RC papers. Without printing, but just softproofing in Photoshop or Lightroom
(with
paper and ink simulation turned on to primarily see effect of paper white
point), it’s
clear that typical profiles maintain the bluish look of the this category of
paper with
both relative and perceptual intent,
This is not correct. You will only get a bluish look for papers with a blue
white
point when using in some sort of absolute colorimetric mode.
I don’t agree, or understand. If the paper is bluish, then the final print has
all my colors skewed towards that bluish paper white, as in relative col. Say
printing a grayscale edited as a* and b* as 0 on a typical bluish paper with
white point of b* -5 to -9, using relative col, the printed greyscale will
measure in non-neutral with negative b* values, as the whitepoint of the paper
has been used/mapped. The whole image gamut have been skewed, and the whole
image appears bluish / less warm than intended.
Wishing more of an absolute match on
colors with my source file - not nessecarily super scientific match, but a
perceptual
match, more as if the paper actually had a neutral white point.
That's what relative colorimetric does.
Relative intent gives me relative colors, as in all colors are skewed to the
papers whitepoint. I’d like my edited images to maintain their hue look when
printed (contrast and saturation will often need compression though). Relative
on blue paper, makes my images look overall bluish. As it’s spec’ed to do. And
absolute makes my in-gamut colors look exactly as I want them - in effect
counteracting the non-neutral paper white, so a neutral greyscale actually
prints neutral, as in maintaining a* and b* 0. Tested and verified. So absolute
is close to my intended wish of not having overall look turn toward a blue
paper white, but of course brutally clips out-of-gamut colors, worst being loss
of shadow and highlight details, without manually limiting beforehand.
So I’d like to somehow make an intent/profile that could ensure tonality with
adequate compression (at least moving black and white point of image to within
paper/printer gamut to avoid clipping, perhaps with BPC), and then _not_ map
white point to paper white, so my colors aren’t skewed towards blue, but
maintain their overall hue, that would be great.
I know perceptual intent can have all kinds of custom unspecified tricks up
it’s sleeve, but as I have long had a wish of solving how to compensate the
bluish look
when printing with my own argyllcms profiles (primarily from Lightroom), I
got very
intrigued. Absolute intent isn’t available from Lightroom, and doesn’t fit
the wish
anyhow, as I would like something like black point compensation to be of use
to me.
Something is wacky with your print workflow if you are getting blueish whites
without selecting some sort of absolute colorimetric or proofing setting.
I would think the workflow is fine. I get, expected, bluish output, if printing
on bluish paper, if using intents with white point mapping (for instance
relative). That’s what they do, and what I’m used to (therefore prefering more
neutral papers that doesn’t require as heavy white point mapping, often
expensive though). What I’d like to have an option for, is to counteract a
paper’s blue tint, so my edited colors on print won’t shift as much towards
that unwanted white point. I know that in effect colors everything yellowish,
and will alter the contrast slightly (as white will now not be paper white, but
actually neutral in tone, by printing compensating yellow).
Again, it could seem i1Profilers mentioned perceptual option for this greyscale
neutralization seem to do that. "The Neutralize Grey slider allows you to force
the greys to become more absolutely neutral by dialing in a lower value or
match the paper more by setting a higher value.” That seem to explain and match
my wish. How to accomplish in ArgyllCMS? Will the "Grey axis alignment factor”
in ArgyllCMS affect some of this, if altered?
I hope that clears up some of the misunderstanding. Trying to communicate this
seems difficult. Thanks for trying to respond.
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