Dan Margulis Applied Color Theory
Creating a 4/c Black and White
Date: Mon, 3 Jan 2005 07:36:07 EST
From:Hal Silverman
Subject: Converting to B/W
Hello and Happy New Year to all.
I just completed shooting a job, where many(24) of the
color images will be reproduced in a brochure as 4 color b/w. Through the
"Channel Mixer," I have converted the images to a monochromatic
state while keeping them RGB. They look great!
Now, how should I go about the CMYK conversion? What
should I look for in keeping the neutral color in the images? I noticed
that in some of the images I converted over while testing, the cmy values
shifted a percentage here and there. I might mention that the images were
shot under the same conditions, so they are very consistent in their
appearance.
I contacted the printer for their recommendation; they
were of no assistance.
Best regards,
Hal
Hal Silverman Studio, Inc.
6511B Basile Rowe
E. Syracuse, NY 13057
p. 315.434.9121
w. www.silvermanstudio.com
___________________________________________________________________________
Date: Mon, 03 Jan 2005 12:59:21 +0000
From: Shangara Singh
Subject: Re: Converting to B/W
It was 3/1/05 12:36 pm, whenHal Silverman wrote:
I just completed shooting a job, where many(24) of the
color images will be
reproduced in a brochure as 4 color b/w. Through the
"Channel Mixer," I have
converted the images to a monochromatic state while
keeping them RGB. They
look great!
Now, how should I go about the CMYK conversion? What
should I look for in
keeping the neutral color in the images?
Stephen Marsh has some good info regarding basic CMYK
separations on his Website. It's in three parts. The info you seek is in
part three, I think. It's worth reading all three parts.
http://members.ozemail.com.au/~binaryfx/index.html
Shangara Singh.
___________________________________________________________________________
Date: Mon, 3 Jan 2005 12:48:32 -0500
From: Terry Wyse
Subject: Re: Converting to B/W
I'd create a "Custom CMYK" profile (I can't
believe I just recommended using the "Custom CMYK" engine) and
set it up for either "Heavy GCR" or "Maximum GCR" with
a Black limit at or near 100% with a total ink of not more than about 300%.
The idea is you want a separation made up of almost exclusively black ink
with only enough CMY to extend the dynamic/density range out to the limits
of what the press can achieve. The other option would be to create a
"traditional" double-black duotone or gray+black duotone.
As a side note, I recently did a bit of press profiling
where I included a total ink chart in the press run. Interestingly (or
not), the highest Dmax's were achieved where K=100% but the total ink was
no more than about 260-280%. At K<100%, the total ink amount could be
much higher (340%+) but in no case did the Dmax exceed the K=100%, TAC=
260-280% combination. FYI, this was on a 6/color 40" Heidelberg
sheetfed press.
Cheers,
Terry
_____________________________
WyseConsul
Color Management Consulting
704.843.0858
http://www.colormanagementgroup.com
http://www.wyseconsul.com (coming soon)
________________________________________________________________________
Date: Tue, 04 Jan 2005 01:05:22 -0000
From:Stephen Marsh
Subject: Re: Converting to B/W
Hal Silverman wrote:
Now, how should I go about the CMYK conversion? What
should I look for in
keeping the neutral color in the images?
Two basic choices - grey balance is your main concern
here, even though using a heavy GCR this is still a concern for lighter
tones.
i) Using a modified default Custom CMYK using Heavy GCR
and whatever dot gain and max K and TIL etc.
This will result in one type of neutral grey balance,
that many printers who are used to working with Photoshop separations over
the years will be comfortable with.
ii) Using an EDITED Custom CMYK setting that has
ALTERED LAB INK VALUES from the default, to produce the grey balance that
you would like to hit, rather than the Photoshop legacy aimpoint. For
example, I have made an ICC profile from Custom CMYK that is very close to
TR001 grey balance (what most mean when they say SWOP). But I would only
use this hacked profile for four colour greyscales.
Now if Adobe and other profile suppliers would be kind
enough to offer freely available Heavy GCR TR001 profiles to the public -
then that would be great. But nobody does. At least Chromix offered UCR and
LT and MED GCR variants of TR001. But nobody seems to care about four
colour greyscale work.
Another 'radical' option is to make your own greyscale
conversion where the image is K only, then to fudge support screens in the
CMY in the deep shadows/three quarter tones. Easy enough to automate.
Stephen Marsh.
___________________________________________________________________________
Date: Wed, 5 Jan 2005 19:03:48 EST
From: Dan Margulis
Subject: Re: Converting to B/W
Terry Wyse writes,
I'd create a "Custom CMYK" profile (I can't
believe I just recommended
using the "Custom CMYK" engine)
I can't believe that in the year of our Lord 2005, that
Custom CMYK is the only option Adobe chooses to give us for dealing with
drop shadows, 4/c B/W, and the like.
and set it up for either "Heavy GCR" or
"Maximum GCR" with a Black limit at
or near 100% with a total ink of not more than about
300%.
Not Maximum GCR. That would give you K only, no CMY at
all. Also, an important note: By default, Custom CMYK underestimates black
dot gain. That's not a big deal when using a skeleton black, but in this
case it *is* a big deal. Ideally one goes in and edits the black dot
gain curve, but for these limited purposes Hal could just increase the
overall dot gain setting by four points before separating.
As a side note, I recently did a bit of press profiling
where I included a
total ink chart in the press run. Interestingly (or
not), the highest Dmax's
were achieved where K=100% but the total ink was no
more than about 260-280%.
At K<100%, the total ink amount could be much higher
(340%+) but in no case did
the Dmax exceed the K=100%, TAC=260-280% combination.
Yup. If you're using a relatively heavy black, trying
to force extra CMY into the shadow is counterproductive, as we discussed
some months ago when various parties found it illogical that the black
generation setting in Custom CMYK supersedes a contrary ink limit.
Dan Margulis
___________________________________________________________________________
Date: Wed, 5 Jan 2005 20:46:20 -0500
From: Terry Wyse
Subject: Re: Converting to B/W
I guess I was thinking more in terms of what
"MaxK" or maximum GCR does in profiling applications. It will
give you mostly black (linear curve shape) but it will add enough CMY to
give you, in essence, a "Rich Black" style of profile. You'll get
enough CMY to add up to your requested total ink limit in most cases. And
of course a profiling app will compensate correctly for the K dot gain as
this is known from the actual press characteristics/measurement data.
Cheers,
Terry
___________________________________________________________________________
Date: Thu, 6 Jan 2005 08:50:30 EST
From: Dan Margulis
Subject: Re: Converting to B/W
Terry Wyse writes,
I guess I was thinking more in terms of what
"MaxK" or maximum GCR does
in profiling applications. It will give you mostly
black (linear curve
shape) but it will add enough CMY to give you, in
essence, a "Rich
Black" style of profile.
What people call that kind of profile is unimportant;
the point is that any method of conversion that professionals are apt to
adopt needs to have the capability of making that kind of separation as an
option.
Also, I hope the profiling app has the capability of
making the type of sep that Photoshop designates as "Maximum"
GCR, i.e., no CMY ink at all where possible. That type of sep is also
necessary from time to time, although not to make 4/c B/Ws. But, if
somebody gives you an image of a comic strip in RGB and you have to
separate it, you want those fine black lines to come out as 0c0m0y100k.
Dan Margulis
___________________________________________________________________________
Date: Thu, 6 Jan 2005 14:57:11 -0500
From: todie
Subject: Re: Converting to B/W
On Jan 6, 2005, at 8:50 AM, Dan Margulis wrote:
...if somebody gives you an image of a comic strip in
RGB and
you have to separate it, you want those fine black
lines to come out as
0c0m0y100k.
… so you'd start by telling somebody that the
comic strip was inked wrong.
The line work should've been scanned at at least 600dpi
(spi/ppi?:) saved as a bitmap TIFF, downsampled to 300ppi (or less), choked
(the oposite of "spread" in old timer speak : ), inked (filled
with color?), saved as another TIFF, than placed in Quark with the line
scan in a color "none" picture box (set to overprint) on top.
Laurentiu Todie
m
___________________________________________________________________________
Date: Thu, 6 Jan 2005 21:59:04 EST
From:Hal Silverman
Subject: Re: Converting to B/W...Follow-up
Hello everyone!
I want to thank you for your input in this recent
thread.
Initially, I had contacted the Prepress dept. of the
printer for their input. It amazes me, on daily basis, what lack of
knowledge there is out there. They were lost as how I should approach the
issue.
I ended up creating a custom profile, using Heavy GCR,
90% black Ink Limit, and keeping the Dot Gain at Standard 17%. This profile
was used after I did the initial b/w conversion using the Channel Mixer,
and keeping the file RGB. I did the initial conversion to CMYK, and found a
bit of Y in the files (1-2% higher than M). The images looked a tad flat
too. I created a curve in the Y channel to neutralize, then another one in
the K to bump the contrast. I did some proofs on the Epson, and was amazed
at the tonal range of the prints. My client was thrilled too. I am eager to
see the proofs from the printer, hoping my approach proves positive.
I must pat myself on the back here, as I used to
avoid CMYK like the plague! But the recent confidence I have gained is all
due to the knowledge from this list, and Dan's book.
Best regards,
Hal
Hal Silverman Studio, Inc.
6511B Basile Rowe
E. Syracuse, NY 13057
___________________________________________________________________________
Date: Fri, 07 Jan 2005 04:32:15 -0000
From:Stephen Marsh
Subject: Re: Converting to B/W...Follow-up
Hal Silverman wrote:
I did the initial conversion to CMYK, and found a bit
of Y in the files (1-2%
higher than M). The images looked a tad flat too. I
created a curve in the Y
channel to neutralize, then another one in the K to
bump the contrast.
Hal, you have made the decision that there is too much
yellow.
WHY???
What are you making this decision off?
If the file was neutral to start with in RGB, then you
convert to CMYK then the CMYK will be neutral, if you mess around with the
CMY curves you can mess things up if not careful.
So, you converted to the legacy gray balance found in
the old SWOP Coated settings - which is NOT TR001, but it is something that
many folk are used to printing for historical reasons.
If you do know the final output condition, then you
could assign this profile to the Custom CMYK Heavy GCR separation, then
view the files numbers as LAB numbers and not CMYK, then you could adjust
things with a more known outcome. But if you don't know the final
conditions and you just decide to pull a yellow curve or whatever - how do
you know what you are really doing?
The other way is to try to hit known neutral CMY
aimpoints over the tonal scale, this way the 'profile' is in your head and
not in Photoshop, and you adjust the CMY to match these target values, is
this what you were doing when you pulled the Y curve?
With the legacy custom CMYK profile assigned to this
image with the yellow curve, what LAB values do you get? I would presume
that Photoshop now thinks this grey is no longer neutral gray. If you had
to convert to RGB or to another CMYK and expected a true neutral for the
new conversion - IT WOULD NOT BE NEUTRAL.
Stephen Marsh.
___________________________________________________________________________
Date: Fri, 7 Jan 2005 08:35:44 EST
From: Hal Silverman
Subject: Re: Re: Converting to B/W...Follow-up
Stephen,
I sort of understand what you are writing.
I was going strictly by the numbers. I did not check in
LAB, but only in RGB and CMYK. You are right though....
The RGB values were identical after the conversion to
CMYK, but I thought the Y and M needed to be identical as well. That's what
threw me. The Y was 1-2% higher.
I guess I took the wrong road!
Regards,
Hal
Hal Silverman Studio, Inc.
6511B Basile Rowe
E. Syracuse, NY 13057
p. 315.434.9121
Adobe Photoshop training classes are taught in the US by Sterling Ledet & Associates, Inc.