[texhax] CMYK color v. RGB

[William Adams]

On Dec 19, 2008, at 7:12 AM, Niall Mansfield wrote:

> We've just had a book printed, and there are a few color problems:
> more or less consistently, some blues come out looking a little
> too green, and others look purple.  The printing company say this is  
> probably due to
> the RGB -> CMYK color conversion, and say that we should
> ensure images are in CMYK format rather than RGB before
> they are embedded in the PDF.
>
> We're using LaTeX, Xfig, GNUplot, Metapost, and all the usual
> tools on Linux.  We produce the book as PostScript, and then
> ps2pdf that, to send to the printers.
>
> I don't think it's possible for us to use CMYK.  Is it?
> Does anyone else have experience of similar problems?

Sure it is. You just need to introduce a step where you colour- 
separate (and if necessary adjust) all images. You'll also need to  
specify any colours for text or vector elements using CMYK (post- 
processing them if need be in a pre-press-oriented tool like FreeHand  
or Adobe Illustrator).

In theory you could adjust so that they display nicely w/ an RGB  
colour profile which has a gamut which your printer can separate to in  
a fashion you find acceptable and tag the images w/ that profile and  
then the separation would work, but that demands colour-calibrated  
displays &c.

> ps: we had advance review copies printed digitally.  They were
>     fine; only the litho copies were weird.  The printers say
>     it wasn't a problem with their inking of the litho machine,
>     and insofar as I understand what they are talking about, I
>     believe them.


The digital machines are usually RGB-oriented and have a wider gamut  
than machines which have to print ink in multiple passes.

You should've gotten a colour-separated contract proof which the  
printer was able to match on press.

William

-- 
William Adams
senior graphic designer
Fry Communications