RGB => CMYK Conversion and back

janbakjanbak Registered Users Posts: 7 Beginner grinner
edited December 14, 2009 in Finishing School
Could you explain what are the problems of this kind of conversion?

I explain what I've understand:

assuming that I start with an RGB image, I require a final RGB output and that RGB is a wider workspace than CMYK

- if I make some changes in RGB and then I convert ti in CYMK I can loose something

- but, if my first step is RGB => CMYK conversion, and I make my first changes in CMYK and then I convert again in RGB I shouldn't loose mothing because RGB is wider then CMYK, at this point in RGB I can made futher changes

... is my reasoning correct?

Thank you very much ;)

Comments

  • arodneyarodney Registered Users Posts: 2,005 Major grins
    edited December 14, 2009
    janbak wrote:
    Could you explain what are the problems of this kind of conversion?

    Lots of them:

    You reduce the color gamut by a lot depending on the source RGB color space which you can never get back when converting to CMYK.

    You build in black generation that’s specific to the print process. That should come from an RGB source which of course has no black. If you start with a specific black generation and go back to RGB, that’s hosed like the gamut.

    There’s data loss but at least do so in 16-bit or you really toss away a lot of useful data.

    The CMYK file is larger, has less data, less gamut and is specifically optimized (in the conversion from RGB) to a specific printing device. Its a sex change operation. You may be happy with it, but there’s no going back.
    Andrew Rodney
    Author "Color Management for Photographers"
    http://www.digitaldog.net/
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