Regarding color conversion (RGB->CMYK)

Cy Edmunds cedmunds at
Sat Nov 13 03:43:32 CET 2004

"Johan Holst Nielsen" <spam at> wrote in message 
news:4194bd54$0$75308$edfadb0f at
> Hi all,
> I hope someone can help me.
> I have do do a color conversion from RGB to CMYK. It's harder than I 
> thought :D Anyway, here is my problem.
> I tried some differents ways to do it - I have a TIFF RGB file that I need 
> to convert to CMYK colorspace.
> First of all I tried ImageMagick - it works - or it doesn't. Its give me 
> an CMYK TIFF - but with way wrong colors :( Nothing seems to be quite 
> right in that picture - tried google - and it seems that other people have 
> the same problem as me :(
> After that my thoughts was on PIL (Python Imaging Library). The colors was 
> better - but to bright - cause it didn't include K (so it was basicly a 
> RGB=>CMY conversion - Black is 100% Cyan, Magenta and Yellow).
> I tried some googling - and again - some people said that PIL shouldn't be 
> used for images that should be printed "professional".
> Now, I don't have any clue about what I need to do? Is there another way 
> to solve my problems? Any tools that can convert somehow? Or any kind of 
> examples I can try to read?
> It have to run on a Linux box - Python, Perl, PHP, bash whatever :(
> Though about GIMP - but can find any information about how I can do a 
> conversion in command-line? Any one having knowlegde about this?
> Looking forward to hear from you and I will appreciate any kind of help.
> With Best Regards,
> Johan Holst Nielsen

There is no simple way to convert RGB to CMYK for the simple reason that 
CMYK is a device dependent color space. (Actually, unless it is calibrated 
somehow RGB is a device dependent color space also.) A good way to do the 
conversion is to get the ICC profile for the device that made the RGB and 
another ICC profile for the device which will print the CMYK and convert one 
to the other using a color management module -- aka a CMM. I don't know if 
ImageMagick can do this for you or not but it would be very hard to get the 
colors right any other way.


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