Re: UCR vs GCR...or Neither - RAW CMYK?


Dan Margulis <76270.1033@...>
 

Stephen writes,

I use one of those expensive Scitex scanners you mention - and I would
have to agree with your take on their default tables black generation. I
have not been able to make a custom black generation curve in Photoshop
that even comes close.>>

The question is why you would want to. The whole point of variant black
generations is that theoretically the colors remain the same--in principle
Heavy GCR gives the same result in print as UCR. In practice it doesn't,
but the difference between Photoshop's Light GCR and Scitex's is going to
be very small in the overall scheme of things.

In part this is due to how hard the black generation curve is to edit -
and that Photoshop _only_ gives the option of UCR or GCR separation
methods.>>

*All* separations, saving those that are CMY only, are UCR or GCR.

The Scitex scanner in default CMYK tables settings scans into
CMYK with GCR and UCR turned OFF. You get 'raw' CMYK.>>

There isn't any such animal. The scanner records R,G, and B data which
becomes, with mild variation, C, M, and Y. The black data is calculated
from the other three--there are no CMYK-native scanners.

It seems that CMY are used throughout the image to describe neutral
tones. I guess this is similar to using GCR with no black generation.>>

No, this is traditional UCR, black only appearing where necessary to
achieve darkness, not to hold neutrality.

Now I use GCR light black or UCR most of the time, unless more black can
help (when doing Photoshop seps). This is very much an individual image and
output based decision - gone are the days when one setting suited all (now
that I know better). I have not reached this level on the scanner yet.>>

Your policy is a good one, but I doubt that it's worth worrying about
extending it to the scanner. When you run across something that needs a
nonstandard black, do it in Photoshop-it's a lot easier. Four years ago, in
reviewing the new Scitex line, I wrote:

"Basic scanning may be easy, but the exceptions are lethal. Scitex's has
several sets of preset CMYK parameters for different printing
conditions--but, unbelievably, none for the most common of all, SWOP. Users
can create these parameters for themselves--if they happen to be one of the
twenty or so individuals on the planet capable of figuring out Scitex's
exceedingly opaque implementation of black generation."

Dot gain is never explicitly mentioned in the scanner software.>>
Dot gain and black generation are different animals. If you believe that an
image will correct or print better with a higher black component, that
decision would presumably the same on either 100# Kromekote or newsprint.

But from what you are saying, knowing the amount of UCR or
GCR is pointless without knowing the black generation method,
as in the start point for black?>>

In order to conceptualize the kind of black that's being generated one
needs to know the start point of the black and the how the slope of the
curve varies. A percentage is only going to be relevant at one point on the
curve. In darker areas, the percentage of black will be higher and in
lighter areas it will be lower.

I thought that the use of the term 50% GCR was an old drum scanner or
traditional separation terminology.>>

It's sort of like the percentages used in the "Amount" field of the Unsharp
Mask filter or the dot gain percentage in CMYK setup. The user doesn't need
to know what the percentages mean, just that a higher percentage increases
the effect. Unlike these two, however, which *do* have meanings that an
interested user could find out, "50% GCR" is meaningless without further
explanation, except that it probably generates less black than 60% GCR.

Many printers still list this in their separation spec sheets - instead
of the more 'regular' or 'standard' Photoshop terminology. But just like
SWOP, they do not mention a start point
- only the amount of UCR or GCR.>>

Sure, and many others express their column width in pica ems, or indicate
that they have 2% dot gain.

Dan Margulis

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