[Chimera-users] RGB->CMYK color conversion

Greg Couch gregc at cgl.ucsf.edu
Tue Nov 1 13:20:04 PST 2005

On Mon, 31 Oct 2005, James Puckett wrote:

>   I am writing to see if there are suggested methods for ensuring
> good color conversion of rendered Chimera images from RGB to CMYK in
> Photoshop (or other image editing programs).  When printing to a
> Tektronix Phaser 740 color laser, I am getting poor correlation
> between screen colorings and the printed ones.  I have heard that the
> CMYK color space is basically a subset of the RGB color space.  If
> this is actually the case, is there a recommended way to pick RGB
> colors that are relatively "safe" for conversion to a CMYK color space?

Matching screen and print colors is getting easier.  If you have Adobe 
PhotoShop, the best thing to do would be to read its help information on 
"Producing Consistent Color" and follow those recommendations.  Microsoft
has a website <http://www.microsoft.com/whdc/device/display/color/icmwp.mspx>
about "Color Management and Windows" that discusses many of the same
issues.  For Apple's Mac OS X, read about its ColorSync technology,
<http://www.apple.com/macosx/features/colorsync/>.  All of the above color
management systems use ICC color profiles (<http://www.color.org/>).

The basic idea is that you need a color profile for your screen and your 
printer and those profiles are used to match the colors.  The color gamut
of a screen and a printer vary greatly -- screens are much brighter than
printers, but printers can produce colors that screens can't and are
good at subtle differences in dark colors.  Luckily, manufacturers usually
provide an ICC color profile -- but to get the best results you'll need
create your own using a colorimeter (e.g., <http://www.colorvision.com>).

For Windows, if you do not have a printing program that supports color
profiles, you can use the free ICC Profile Conversion Software from Draw
Creek Photo, <http://www.drycreekphoto.com/tools/profile_converter/>.

 	Good luck!

 	Greg Couch
 	UCSF Computer Graphics Lab
 	gregc at cgl.ucsf.edu

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