[clue-tech] gimp CMYK follow-up

[Michael J. Hammel]

On Fri, 2004-12-31 at 19:49, Match Grun wrote:
> I believe that there is limited support for CMYK in Gimp... it must be
> there since my Epson printer use CMYK. 

Support for your printer is actually handled in GIMP-Print (which is
changing its name, I believe, to Gutenprint).  The CMYK output is
generated by that, which has a GIMP plugin.  Note that GIMP-Print is a
standalone project that has very little to do with GIMP itself (which is
one reason for their wanting to change the name).  GIMP-Print also works
hand in hand with the CUPS printing subsystem.

> However, I believe that the
> publication business requires CMY color separations. Maybe that is what
> is missing from GIMP.

Color separations in output files is not supported yet.  Support for
this is waiting on GEGL, which is a color management (re: color space
management) infrastructure that will do a lot more than just CMYK.

Also, being able to convert between color spaces would allow you check
for out of gamut conditions given an ICC profile (if available).

> CMY does not require 16-bit to work. Even in products such as Photoshop
> that is relatively new. There was limited 16-bit support in versions
> prior to CS. CS is all 16-bit.

16 bit support is primarily being requested by the film industry, both
still and video.  The continuous tone images produced by film can lose a
lot of quality when converted to 8-bit channels, so 16 bit is a
requirement for visual effects (for example).  CinePaint is a 16 bit
version of GIMP 1.0 designed specifically for this purpose.  There are
no plans currently to merge CinePaint and GIMP and both projects are
happily extending their features on their own.

> However, 16 bit support is desirable... my Nikon produces 12-bit images,
> so Gimp forces me to lose 4-bits somewhere along the way. Now that is 

Is that 12 bits per channel in hardware?  If so that would probably
require 16 bit channels to be lossless but if its actually 8 bit in
hardware and 12 bits in software then it probably doesn't matter (though
it might help).  Don't hold me to that - it's just something I've been
told in the past.

> Also, Photoshop does support for ICC profiles which is probably the most
> important feature missing from Gimp.

ICC profiles are supported by GIMP-Print for printing but GIMP itself
does not yet know what to do with those.  I suspect that will change
once GEGL is integrated.

Monitor profiles are not yet supported by Linux, though I think (and
could be wrong about this) if it was supported it would be a feature of
the X server and not GIMP.

> It is interesting to note that professional photographers and Photoshop
> gurus recommended submitting TIFF files with 8-bits per pixel for print
> publication.

It is the most common, full color and alpha channel supporting, lossless
format for raster images.  Inkjet printing is not continuous tone
printing so 8 bits per channel is fine.  High end printers are
continuous tone but full color prints on those are expensive.  For all
but the most high end work, 8 bits is probably sufficient.
-- 
Michael J. Hammel - mjhammel at graphics-muse.org - XEUS: www.ximba.org
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Idiocy:  Never underestimate the power of stupid people in large crowds.