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Path: utzoo!mnetor!seismo!rutgers!clyde!motown!mergvax!tkxyv
From: tkxyv@mergvax.UUCP (William Klein)
Newsgroups: sci.physics,comp.graphics,comp.sys.ibm.pc
Subject: Re: Color questions
Message-ID: <153@mergvax.UUCP>
Date: Mon, 15-Jun-87 12:19:09 EDT
Article-I.D.: mergvax.153
Posted: Mon Jun 15 12:19:09 1987
Date-Received: Sun, 21-Jun-87 08:38:49 EDT
References: <307@msunix.UUCP>
Organization: Allied - Linotype , Hauppauge NY
Lines: 66
Summary: laser output, color, graphics arts...
Xref: mnetor sci.physics:1706 comp.graphics:804 comp.sys.ibm.pc:4915

In article <307@msunix.UUCP>, jon@msunix.UUCP (Jonathan Hue) writes:
> ...
> come up with tables for the conversion.  Make sure you can map the colors
> from the process book exactly (have an RGB triple in your system that
> maps to a CMYK quad which is a process color) to keep the Graphic Arts
> types happy.  Or you can use the process color book, and match those
> to the monitor by eye.  Don't laugh, I know some people who have done
> just that.  Another way would be to model the absorption of light by the
> inks to come up with tables.  I'm too much of a feeb at Math and Physics
> ...
> One important thing that I forgot to mention is that the inks used in
> printing do not absorb light like an ideal ink.  As I recall, yellow ink
> ...there is no simple formula, despite what a lot of uninformed people think.
> As far as resolution goes, typical output scanning for good quality
> magazines (continuous tone art) is 12dots/mm (304dpi), with 255 different
> dot sizes.  Also, each layer of dots is at a different angle, and the dots
> can be round, square, or elliptical.  If there is a laser printer out there
> capable of printing 192dots/mm (that's > 4800dpi!) on a transparency, there
> are a lot of Hell flatbed laser scanner owners that would be interested
> ($500K a pop!).  I find it hard to believe that a "high resolution" laser
> printer could produce anything except rough comps.  Final separations,
> no way.  If these numbers are making you laugh, you've never seen
> a Graphics Arts department manager whip out his loupe and start looking at
> screen angles, dot shapes, and dot sizes.

At Linotype we make equipment for the graphics arts industry. The odd thing
about this industry is that the money (in color, at least) is where the
quality is. We have just evaluated our high resolution laser output printer
for its suitability for color work, and it is just barely good enough to
do kind of lousy color proofs (in the words of a graphics arts dept mgr).
This device outputs 2540 dpi, with an error across the whole raster (for
newspaper or wider widths) of <60 microns. No slouch, but nowhere near good
enough for color work. Indeed, you do need ~5K dpi to get good color output.
And the error must be extremely low for screen registration: the eye is
amazingly good at picking up moire (beat frequencies between the different
colored dot screens in the space domain) which can be caused by only a few
microns of misregistration between the screens.

The kind of color photographs that you see on the covers of Vogue, Life,
National Geographic, etc. go through an incredible number of iterative
proofs which involve one test print after the other being passed by the
customer for color checks, overall impression evaluations, and all kinds
of subjective judgements. Not easily automatable (yet, where are you AI and
CE people!?!).

Forget electronic (screen) proofing: you can't get color anywhere
close (to a graphics arts person) on the screen to what the ink will look
like. You can't even print proofs that look close enough for many customers
without actually printing the proofs on the same press, using the same ink
and paper as will be used on final output. Some customers even have a
'standard' light which will illuminate the proof with a known set of 
frequencies for the color evaluation. (A printed color photo will look
quite different under tungsten light, flourescent, 'warm' flourescent,
and daylight conditions).  With all of these variables, most of what the
video pre-proofing is used for is cropping, some editing, perhaps some
drawing (esp in ad layout) and the like. No color adjustment.

Perhaps when we get video monitors with 60K by 40K pixels, and a RFB and
blit engine fast enough to draw them all in a short time, and some kind
of standard colors... (:-))

-- 
Life is what happens to you when you are busy making other plans.
Real Life: 		W. Ted Klein
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VOICE:			516-434-2687