Re: [ECI-EN] RGB to CMYK with ISO web coated profile
4 Aug
2004
4 Aug
'04
10:49 a.m.
Andy
When you do a relativ Colormetric Conversion from AdobeRGB to ISO Web
Coated, a different way of gray-generation gets used as of perceptual.
Since in a print run the yellow color is (usually) the last coler,
Heidelberg (Profiles are done with Heidelberg PrintOpen) found that the
yellow color is often reflecting and the color gets lighter the more
yellow is on the sheet in a darkgray area. Therefor in the RelCol RI,
the yellow color gets reduced a little bit more. Even at about 85%
Gray, the values of yellow stall or drop when the color gets darker.
When you separate using the Perceptive RI, you will find CMYK-Values
that you would more consider as to be gray. But in real world pint
production, you will not see much difference.
Maybe Mr. Bestmann from Heidelberg cann explain that better.
rgds
Peter Kleinheider
Am 03.08.2004 um 22:46 schrieb Andy Psarianos:
Paul,
Thanks that's really helpful.
Yes indeed I am talking about the latest release of the profile called
"ISO web coated"
For example if I convert the following values I get the following
results.
From RGB Adobe 1998:
RGB 50,50,50 to "SWOP" CMYK = 70,64,63,62
(C highest and M and Y are similar values)
RGB 50,50,50 to "ISO web coated" CMYK = 64,53,48,71
(C highest M in middle and Y lowest)
I'm not saying SWOP is correct, but if I were to remove the black
separation it would appear grey wouldn't it? I don't believe the
values in the ISO web coated values would be neutral. If this is the
case, the question is why?
I do understand that the lack of yellow in the dark greys could be
hidden by the heavy black, but I don't understand why this was done,
and why a more "conventional & balanced grey" was not chosen. Is it
simply that when printing shadows with equal amounts of m and y they
have a "yellowish hue" or is this an ink trapping issue?
Overall, all tests I've done with the ISO web coated profile in
conversions results have been very good. I'm willing to accept that
these "unconventional values" in principle are OK, although I have
several sceptics here which I need to convince.
I would like to know what the reason was for this choice, if indeed it
was a choice.
Can anyone help shine some light on this decision?
many thanks
Andy Psarianos