UCR vs GCR


Dan Margulis <76270.1033@...>
 

Gordo writes,

I would like feedback on forum member's understanding of how color
separations are done in Europe, America, and Asia. I have been told that
the following are representative numbers:>>

From what I've seen there's little difference in black generation practice
internationally. The same pluses and minuses apply: with a heavier black,
one risks muddier images, and they're harder to correct in Photoshop. OTOH
a heavier black will hold neutrality better, and also make it easier to
print the job in register, or rather make a misregistered job look more
acceptable.

Photoshop's "UCR" setting produces a lighter, higher-contrast black than
its "Light GCR", but for printing purposes I think there is little
practical difference. "Medium" or "Heavy" GCR would change the process, in
some ways for better and in some ways for worse.

Although there are some people who swear by one method or another, the
truth is that it doesn't make that much overall difference *unless* one is
making decisions image-by-image, in which case it can be a big deal.

Printers who insist on one method or another generally are completely out
of touch. Right now, their clients can be divided into those who know what
they're doing, in which case they are probably using a skeleton black, and
those who don't, who are probably using the Photoshop default of a heavier
black. Yet from time to time both groups get good results.

in Europe
- Newspaper printers use GCR of about 240>>

The 240 is a total ink limit, having nothing to do with one's GCR decision.
240 is also pretty standard in the U.S. Because newspaper black isn't as
rich as elsewhere, and because registration problems are common in
newspapers, there is a school of thought that believes in relatively heavy
GCR, although I don't think it's the majority.

- Rotogravure use primaraly UCR of about 310 (might also be GCR)>>
That 310 should be a *minimum*, not maximum shadow. There is no upper ink
limit in gravure. A very light black is certainly traditional in gravure
but I don't really understand why. The two main drawbacks to using more
black in offset don't apply. Large solid or semi-solid inked areas don't
automatically create higher densities elsewhere, as they do in offset.
Also, a major cause of excessive black inking in offset is a desire to make
the type more readable. In gravure, which is ordinarily CMYKK, that
objection doesn't apply because the type is on a separate cylinder from the
images.

- Commercial web offset use primaraly UCR of about 310>>
310 is a reasonable limit although somewhat higher than in the United
States. Again, the more knowledgeable users are generally using a light
black but they're probably not in the majority.

- sheetfed offset: usually no GCR>>
Here is the only area where I think there may be a difference. A lot of
European printing features an *extremely* short black. If you have access
to any Heidelberg software for separating, you'll see an example. Shadow
value in such a method is likely to be on the order of 98c88m88y65k,
whereas in the U.S. you'd be more likely to encounter 85c75m75y80k.

Dan Margulis


Gordon Pritchard <gordon_pritchard@...>
 

What about % of usage rather than how it is done?

What percentage of US sheetfed printers use UCR for their separations as
opposed to GCR?

What percentage of US web publication printers use UCR for their separations
as opposed to GCR?

How does that usage compare to Europe and Asia?

thx


Gordon Pritchard
Commercial Print Specialist
CreoScitex
Vancouver Canada
T: 604.451.2700 ext 2870
C: 604.351.2437
gordon_pritchard@...
http://www.creoscitex.com

Print - dot's what it's about!<
----------
From: Dan Margulis
Sent: Thursday, October 4, 2001 5:22 AM
To: Color Theory
Subject: [colortheory] UCR vs GCR

Gordo writes,

I would like feedback on forum member's understanding of how color
separations are done in Europe, America, and Asia. I have been told that
the following are representative numbers:>>

From what I've seen there's little difference in black generation practice
internationally. The same pluses and minuses apply: with a heavier black,
one risks muddier images, and they're harder to correct in Photoshop. OTOH
a heavier black will hold neutrality better, and also make it easier to
print the job in register, or rather make a misregistered job look more
acceptable.

Photoshop's "UCR" setting produces a lighter, higher-contrast black than
its "Light GCR", but for printing purposes I think there is little
practical difference. "Medium" or "Heavy" GCR would change the process, in
some ways for better and in some ways for worse.

Although there are some people who swear by one method or another, the
truth is that it doesn't make that much overall difference *unless* one is
making decisions image-by-image, in which case it can be a big deal.

Printers who insist on one method or another generally are completely out
of touch. Right now, their clients can be divided into those who know what
they're doing, in which case they are probably using a skeleton black, and
those who don't, who are probably using the Photoshop default of a heavier
black. Yet from time to time both groups get good results.

in Europe
- Newspaper printers use GCR of about 240>>

The 240 is a total ink limit, having nothing to do with one's GCR
decision.
240 is also pretty standard in the U.S. Because newspaper black isn't as
rich as elsewhere, and because registration problems are common in
newspapers, there is a school of thought that believes in relatively heavy
GCR, although I don't think it's the majority.

- Rotogravure use primaraly UCR of about 310 (might also be GCR)>>
That 310 should be a *minimum*, not maximum shadow. There is no upper ink
limit in gravure. A very light black is certainly traditional in gravure
but I don't really understand why. The two main drawbacks to using more
black in offset don't apply. Large solid or semi-solid inked areas don't
automatically create higher densities elsewhere, as they do in offset.
Also, a major cause of excessive black inking in offset is a desire to
make
the type more readable. In gravure, which is ordinarily CMYKK, that
objection doesn't apply because the type is on a separate cylinder from
the
images.

- Commercial web offset use primaraly UCR of about 310>>
310 is a reasonable limit although somewhat higher than in the United
States. Again, the more knowledgeable users are generally using a light
black but they're probably not in the majority.

- sheetfed offset: usually no GCR>>
Here is the only area where I think there may be a difference. A lot of
European printing features an *extremely* short black. If you have access
to any Heidelberg software for separating, you'll see an example. Shadow
value in such a method is likely to be on the order of 98c88m88y65k,
whereas in the U.S. you'd be more likely to encounter 85c75m75y80k.

Dan Margulis


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Dan Margulis <76270.1033@...>
 

Gordo writes,

What about % of usage rather than how it is done?>>
I doubt that anyone has reliable information on this. You may in fact be
the first person in the history of the world who has ever asked this
question.

What percentage of US sheetfed printers use UCR for their separations as
opposed to GCR?>>

In the US I don't even know what the percentage would be of printers who do
their own seps. I would guess that this might be higher for sheetfed than
for web.

We also fall victim to a terminology trap here--there's no real agreement
on what constitutes a "UCR" sep, other than that it's a subset of "GCR". I
usually employ what Photoshop calls "Light GCR", but if pressed, I would
describe this as being a "skeleton black", not "GCR". Other people might
disagree.

I suspect that the answer probably depends on how many printers use
expensive scanners and scan directly into CMYK. If so, they're almost
certainly going with the manufacturer's default, which is ordinarily a
light black, UCR style, but Scitex products will produce a darker black
than Screen products which in turn produce a darker black than anything
from Heidelberg/Linotype/Hell. If they're using Photoshop to make the seps,
odds are that they're going with a heavier GCR, because most printers don't
know much about the topic--the knowledge, if anywhere, is in prepress, and
it's fairly rare there.

What percentage of US web publication printers use UCR for their
separations as opposed to GCR?>>

Probably the most telling point here is that SWOP itself, the nominal
standard-setting organization for publication printing, is close to
clueless about GCR. Rather than just use the Photoshop terminology, here's
what they have to say:

"Current recommendations suggest that a safe range of GCR to use is between
30% and 60%. A 50% GCR setting removes 50% of the gray component normally
produced by the chromatic color and compensates by adding an equivalent
amount of black."

This naive description is roughly equivalent to me telling you that I would
like to meet you at 2 p.m. today on the corner of First and Main, without
telling you in what city. Any sane method of GCR will use a relatively low
percentage of black in light grays and a relatively high one in darker
grays. The SWOP definition is meaningless, worthless. And if SWOP doesn't
know what it's talking about, how can we expect the individual web printers
to?

Dan Margulis


Ruud uit het Instituut
 

Dan Margulis wrote

We also fall victim to a terminology trap here--there's no real agreement
on what constitutes a "UCR" sep, other than that it's a subset of "GCR".

You're right. IMO the terminology went wrong when vendors started to make
their own definitions. I worked with the old Magnascanners from Crosfield.
There I could choose between UCR and PCR or a combination of those two.
UCR = Under Color Removal
PCR = Poly Color Removal
The difference between those two was that UCR was only active in the
neutrals and PCR in the colors.
But PCR was in fact the same as the german definition 'unbunt' on the Hell
scanners or the American GCA (Gray Component Addition) and it's opponent
GCR.

So UCR and GCR both mean the same and are active in the neutrals (the L axis
in Lab).
PCR, unbunt and GCA are also the same and use the combination of all three
axis in Lab.

Excuse my English, I seem to have a Dutch accent.

Ruud de Korte


Ruud uit het Instituut
 

Oops, to fast..

I wrote
But PCR was in fact the same as the german definition 'unbunt' on the Hell
scanners or the American GCA (Gray Component Addition) and it's opponent
GCR.

Last thing was wrong,
GCR has nothing to do with GCA, it's the same as UCR, I shouldn't mention it
in that sentence.

Ruud de Korte


Dan Margulis <76270.1033@...>
 

Ruud writes,

So UCR and GCR both mean the same and are active in the neutrals (the L
axis in Lab).>>

It's clear that there is a lot of misunderstanding of this important topic
on the list so let me try to clarify what the terms mean and why they are
ambiguous.

In RGB, all colors are unique. If you know the values that make a certain
color, there is no other set of RGB values that make the same color. In
CMYK, this is not necessarily true. 120r120g120b is a gray that can only be
produced one way in RGB. The equivalent in CMYK is in the vicinity of 50k,
or of 60c50m50y, or of any mixture of the two: the more black being used,
the less CMY. Therefore, one could have zero black, or 50% black, or 7% or
12.5% or whatever one wants, and still produce the same gray.

The same would be true of almost any color: remove CMY, and you can add
black. Even something as colorful as a face *could* have some black in it,
although it isn't customary. Only a truly saturated color, such as
70c50m0y, could not have black, because in order to add black, you have to
subtract CMY, and there isn't any yellow to subtract.

The basic tradeoffs in a heavier black is that you accept the risk of muddy
reproduction if either black comes down unexpectedly heavily or you don't
have a good handle on what black dot gain is. Also, it's more difficult to
color-correct images in Photoshop when they have a heavier black. As
against that, there will be fewer unwelcome changes in color, and if the
image is going to press, it will be easier to hold in register.

There is a tiny minority of fanatics who hold that one should always print
with as much black as possible (in Photoshop terms, Maximum GCR with
significant UCA). The remainder of the world realizes that all the benefits
of a heavier black are there if one only uses about half that amount in
colored areas. Going further, the majority of experienced CMYK
practitioners, but not all, prefer much less black than even that. This is
where the terminology confusion sets in.

Assume that you are a person who hates the idea of black ink and would just
as soon print entirely in CMY. That sounds like a reasonable philosophy,
but you have to make certain exceptions. Your deepest shadow will be
something like 100c95m95y. That will be too light and too red. So, if you
are sane, you have to add around 50k.

100c95m95y50k, however, is a total inking of 340%, which most printers
won't accept. Therefore, even though you hate black, you are forced to add
more of it here, so that you can lower the other three values and thus get
a lower total ink. Thus, addition of black, removal of the undercolors
(UCR=undercolor removal).

This is why in the type of image discussed by Hector, all the shadow detail
migrates to the black--the CMY channels have to be suppressed because of
the total ink limit.

For most types of printing black only necessarily will appear in dark
neutral colors, as Ruud suggests. However, for poorer types of printing,
such as newspapers, the lower total ink limit will force the use of black
in colors such as navy blue, even if the type of separation is UCR.

There wouldn't be much disagreement as to where the black would absolutely
*have* to appear. The problem is, confining black to only those areas isn't
workable. You wouldn't want to wait until 95c85m85y0k was reached and
*then* start adding black. The gradation in all four inks would be enormous
as the shadows got darker and the job wouldn't be printable. Instead, the
black has to start in areas that are at least slightly lighter so that it
doesn't get so dark so fast. And, of course, there is zero agreement as to
where it should start.

GCR--gray component replacement--means the use of even more black. But
again, nobody agrees as to how much more, where to start it, or how fast to
add it. If the software expresses GCR in a percentage, about all you know
is that 40% will give more black than 35% would. In Photoshop, "Light GCR"
means more black than UCR, and "Medium" means more than light. In practice,
"UCR" and "Light GCR" mean almost the same thing, "Medium" is much stronger
than "Light", and "Heavy" is a bit stronger than "Medium".

The advantages and disadvantages of a heavier black will be most pronounced
in subtle colors. For example, I just created in RGB a typical green for a
leaf, and separated it five different ways. The results are:

UCR: 60c20m81y1k
Light GCR: 59c18m80y2k
Medium GCR: 56c14m77y7k
Heavy GCR: 55c11m76y10k
Maximum GCR: 46c0m69y24k

No matter how heavy the black runs on press, it won't muddy up this color
if you are using UCR or Light GCR. Anything higher is a risk. OTOH, if your
agenda for the image is very subdued colors, having more black will help
insure that nothing goes wrong. In theory, all of these black generations
will give the same result. But as we do not live in a perfect world, in
practice they do not.

Dan Margulis


aaronkiley <aaronkiley@yahoo.com>
 

--- In colortheory@y..., Dan Margulis <76270.1033@c...> wrote:
UCR: 60c20m81y1k
Light GCR: 59c18m80y2k
Medium GCR: 56c14m77y7k
Heavy GCR: 55c11m76y10k
Maximum GCR: 46c0m69y24k

No matter how heavy the black runs on press, it won't muddy up this
color
if you are using UCR or Light GCR. Anything higher is a risk. OTOH,
if your
agenda for the image is very subdued colors, having more black will
help
insure that nothing goes wrong. In theory, all of these black
generations
will give the same result. But as we do not live in a perfect
world, in
practice they do not.

Dan Margulis
I have a question about "kinds" of black. (assuming all the
following would be light GCR)... Does a shadow made with higher black
ink, (73c 63m 63y 91k) versus the same total ink shadow made with
less black (80c 70m 70y 70k) have roughly the same look? If so, is
it increasing contrast in the black channel that makes a shadow look
blacker? I'm trying to reverse engineer some images that were
corrected by someone else. They have a very solid black "look" with
a ton of shadow contrast. The only way I can get this look on screen
is a huge black contrast curve. ... Aaron