[Openicc] Introduction / Gutenprint

[Robert L Krawitz]

   Date: Sun, 10 Apr 2005 16:34:40 -0500 (CDT)
   From: Bob Friesenhahn <bfriesen at simple.dallas.tx.us>

   From what I see, the role of application software stops at
   producing RGB or CMYK output, after which the image (or document)
   is passed to the printer driver for any additional processing.

But what's the interpretation of the RGB or CMYK data?  Is it sRGB, or
some other color space?  If I tell you that my RGB values are
(101,176,82), what is the exact color that my eyes see?

								   If
   this is true, then there should be no need to discuss the exotic
   color models used by some printers since that is a problem for the
   printer driver to take care of.  It is the whole point of having a
   driver.

>From an application standpoint (unless the user is extremely
sophisticated), that's correct.  But what about at the color
management level?

   It seems pretty clear that color management at the application
   "workflow" level is considerably different than color management of
   complicated output devices with more than four inks.

   In the case of printers with many non-standard inks, processing which 
   would normally have been done in the printer's firmware has been moved 
   into the host computer in order to make the base printer cheaper so 
   that more money may be made by selling consumables.  Often the ink 
   cartridges for these printers costs more in total than the printer 
   itself.  Many tricks may be used to obtain better operation from the 
   printer, many of which are not capable of being described by a CMS 
   profile.

These other inks are simply different colors -- different dimensions,
if you will, since each channel can take on a value independent of the
others.  A profile is simply a map between points in one N-dimensional
space to points in a second M-dimensional space.  Why can't a CMS
profile describe these other colors?

I agree that a CMS profile shouldn't try to describe variable drop
sizes (which are simply different drop sizes of the same ink).
Whether a profile should try to describe multi-tone (e. g. light and
dark cyan) is a closer call; in principle they're simply two different
values of the same hue and saturation, but in practice that might not
quite be the case (although the mapping might be able to just take
care of slight errors).  But inks of entirely different hues are
certainly fodder for a CMS system.

-- 
Robert Krawitz                                     <rlk at alum.mit.edu>

Tall Clubs International  --  http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail lpf at uunet.uu.net
Project lead for Gimp Print   --    http://gimp-print.sourceforge.net

"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton