5:51 p.m.
In attempts to convert RGB data to CMYK using the ISO Web coated
profile I've noticed that the values of neutral areas appear to have a
lack of Yellow in comparison to the cyan and magenta separtions (at
least according to what I would expect).
Is there a reason for this that I am not aware of.
Are there any printers out there who have converted RGB to CMYK using
this profile who might be able to give some "in the trenches" points of
view on this somewhat "unconventional" grey balance.
kind Regards
Andy Psarianos
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7:38 p.m.
Hi Andy
Yes it does look a little odd, but works well in practise, due to the GCR
setting I think. This is the latest ISO wed coated icc, as of a few months
ago?
Worked very well for me when a client was given Euroscale coated v2 for
sheetfed images for a wed offset production with lots of neutral consumer
electrical images. I was called in after the first printing!! We changed the
Euroscale coated v2 to ISO web coated with good results when reprinted.
Regards
Paul Sherfield
The Missing Horse Consultancy Ltd
Telephone: 01442 871752
Mobile: 07899 906385
10:46 p.m.
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
On 30 Jul 2004, at 18:38, Paul Sherfield wrote:
Hi Andy
Yes it does look a little odd, but works well in practise, due to the
GCR
setting I think. This is the latest ISO wed coated icc, as of a few
months
ago?
Worked very well for me when a client was given Euroscale coated v2 for
sheetfed images for a wed offset production with lots of neutral
consumer
electrical images. I was called in after the first printing!! We
changed the
Euroscale coated v2 to ISO web coated with good results when reprinted.
Regards
Paul Sherfield
The Missing Horse Consultancy Ltd
Telephone: 01442 871752
Mobile: 07899 906385
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11:03 p.m.
On Aug 3, 2004, at 2:46 PM, Andy Psarianos wrote:
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?
I see this frequently with inkjet printing. If the yellow ink is very
saturated (pure) compared to the other inks, it will take less yellow
to balance the blue produced by cyan and magenta. And some yellow inks
can be fairly green, which would take more magenta to further offset
that contamination in the yellow.
Off hand I can't say what yellow ink hue is being used with ISO web
coated, but this is probably what's going on. This is why color by the
numbers doesn't work unless you know the inkset and the print behavior
of the press/printer very well. CMYK numbers are ambiguous.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0-201-77340-6)
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
4:43 p.m.
On Aug 4, 2004, at 2:49 AM, Peter Kleinheider wrote:
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.
Ahh OK. While this is not defined in the ICC spec, it is possible for
different profile vendors to have different gray balance behavior
between rendering intents, in particular perceptual. Relative
Colorimetric ignores paper white. Because a neutral gray, without any
respect for the paper, is produced with this intent, it's the most
reliable because the human visual system will chromatically adapt to
the paper white (and the corresponding tint in grays due to paper white
showing through).
Gretag Macbeth has an option in ProfileMaker that defaults to this
behavior for perceptual as well. But there is an option to force a
neutral gray WITH respect for paper white. If you were to measure a
gray ramp made in RGB, converted to CMYK using the perceptual intent
with such a profile, the measurement would indicate a neutral gray (a*
and b* = 0 or close to it). The problem with this is that the human
visual system still chromatically adapts to paper white. So a yellow
stock still looks white to the humans, and now the gray ramp will look
very cool in comparison, not neutral. I have found this method of
rendering, taking paper white into account, when it comes to gray
balance to be a waste of time. If anyone has had good results with it
in certain situations, I'd like to hear about it.
When it comes to taking paper L* into account however (which Relative
Colorimetric does not, it assumes paper white has an L* of 100, which
can leader to heavier separations with decreasing paper L*), that's a
good thing.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0-201-77340-6)
10:55 a.m.
Hi Andy
It does look odd, but as Chris Murphy said the yellow can do strange things
within a CMYK grey balance.
I believe this GCR setting within the profile is causing the results you are
seeing, reducing the yellow in a RGB to CMYK conversion to reduce the
possibility of a yellow bias.
The grey balance for ISO for the CMY is:
Cyan Magenta Yellow
Quarter tone 25% 19% 19%
Mid tone 50% 40% 40%
Three qu. tone 75% 46% 46%
But this will not reflect the profile and any GCR that would be applied with
a RGB to CMYK conversion.
As you say the ISO profiles do work well, if the printers follow the
standard printing conditions associated with each profile.
Regards
Paul
The Missing Horse Consultancy Ltd
Telephone: 01442 871752
Mobile: 07899 906385
11:04 a.m.
Paul
This is just a recomendation and does not take in concern any color
cast of the paper.
the issue is: if a printer is printing according to ISO 12647, then the
colors will turn out to be gray on the prints (when doing a separation
of AdobeRGB or ECI-RGB to ISO Web coated)
Am 04.08.2004 um 10:55 schrieb Paul Sherfield:
The grey balance for ISO for the CMY is:
Cyan Magenta Yellow
Quarter tone 25% 19% 19%
Mid tone 50% 40% 40%
Three qu. tone 75% 46% 46%
Peter
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7 comments
4 participants
participants (4)
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Andy Psarianos -
Chris Murphy -
Paul Sherfield -
Peter Kleinheider