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List:       koffice-devel
Subject:    Re: The GIMP 2.0
From:       Thomas Zander <zander () kde ! org>
Date:       2004-01-14 17:26:00
Message-ID: 200401141826.05010.zander () kde ! org
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On Wednesday 14 January 2004 17:34, Paul Campbell wrote:
> On Wednesday 14 January 2004 05:04 am, James Richard Tyrer wrote:
> In a previous life I worked designing graphics accelerators for the mac
> (10+ years ago - for SuperMac if anyone still remembers them),
Memory of them is fading fast.. :)

> CMYK comes out of the print industry, it was born from a world where the
> guy who ran the press would periodically, pull a copy look at it, think
> "hmmm needs more yellow" and tweak a knob. Every print shop had it's own
> color sep algorithm, often different ones for different presses and they
> were guarded as commercial secrets - I've ben out of that biz for a while,
> I'd guess that the advent of an almost entirely digital pre-press has
> probably standardized stuff as bit.

Quite a bit, yes. I still am in that biz; we have the newest Xerox (IGen III) 
streets now (quite cool stuff) and its amazing how much they remind me of the 
simple copiers of 10 years ago. Every simple guy can operate these things...

> The basic 'good' CMYK->RGB algorithm involves 
...
> but I bet 
> they can be loaded from external places (to match a print shop) and their
> formats are either well known or easy to figure out.
The print shop of then are the rips of today; there are many and the price 
varies from being affordable for the hobby-guy to big print-companies.
The point here is that the companies that sell the printers also sell those 
tables as part of the deal nowadays. (really; all of them swallow and print 
RGB nicely!)
I'm just hoping that rgb-cmyk conversion will one day be put in laserprinters 
and other simple printers so linux users don't have to depend on gs anymore..

> > Then there is the issue of color correction so that the screen image will
> > exactly match the printed image, but that is also a different issue.
>
> This is a minefield - many bodies are buried here!
>
> You can't exactly match the screen to the page - pixels and ink don't work
> the same way - you can try and come close which is an appropriate goal.
> There are lots of things you can do with ink (specular reflections,
> opalescent colors for example) you can't do on a screen, and vice-versa
> (really saturated colors)

Right, I think the point to this is that what comes in (via scanner or 
whatever) is will go out with the same color, standardisation and correction 
are needed for the conversion steps. But in contrary to 'real colors',  
'correct color' is something that *can* be done.

> Back at SuperMac we built screen calibrators that measured RGB output
> levels on the screen, played with video card gamma curves to try and fix
> them etc etc all of these things helped a bit - none were perfect (phosphor
> brightness varies over the surface of the screen) - but our marketting
> people kept claiming we were going to produce 'exact matches', made me want
> to grab some of them and shake them around a bit, for all the reasons I've
> given above it just isn't possible - a great goal is a 'good match'.

Hehe; I remember the big Barco monitors which allowed you to color calibrate 
them; creating a exact color profile for that (with a special reader you 
stick on the screen). The barco empoyee that came to do that was around the 
whole day doing the job. He told us the average monitor was about 20% off..
Hardly good enough by any standards...

> Sorry if I've ranted a bit here - I just wanted to pass on some real-world
> experience and give people some perspective on how hard these problems are
> - the math in the books looks easy - in reality it is not.

Well; I dare say an awful lot has been getting better. There are loads of 
newspapers that have a color-correct workflow where photos taken are 
guaranteed to print to the same color every time, and actually have the same 
color as the photographer saw when he took it.
It can be done, but its still far from easy.

Thanx for sharing this :)
- -- 
Thomas Zander
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