HOWTO Convert a ps file to CMYK

Why on earth would you want to convert a ps file to CMYK? Mainly because some journals prefer to deal with figures in CMYK. Why? Because they're in the Printing Business, and the Cyan-Magenta-Yellow-Key colour system is what the Printing Business uses.

The reason is that CMYK represents a subtractive colour system, whereas the RGB (Red-Green-Blue) system is an additive colour system. RGB is used where you are constructing colours by mixing sources of light (eg Computer Monitors) and CMYK where you are constructing colours by mixing absorbing dyes (eg Printing).

The point is that the image you print out won't look the same as the one on your screen. Converting to CMYK ensures that the screen-image and the print-image will be approximately the same.

How To do it

Ok, so, the best I can do is show you how to convert from RGB ps to CMYK pdf. As far as I know gs (ghostscript) doesn't support CMYK postscript. Anyway, use this script as follows:
ps2pdfcmyk foobar.ps
The output will be
foobar_cmyk.pdf
Viewing the PDF, you'll see the colours are somewhat less intense - this is CMYK.
-Dan
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