Re: rgb to cmyk conversions
Re: rgb to cmyk conversions
- Subject: Re: rgb to cmyk conversions
- From: email@hidden
- Date: Mon, 27 Feb 2006 15:47:29 -0500
Liz,
Points to ponder regarding the methods Dan Margulis recommended:
1. In general assigning an incorrect profile rather than doing the convert is inadvisable
when the destination color space has different color primaries than the source. Doing so
will induce hue shifts. This is the case with sRGB and Adobe RGB, although hue dependent shifts
are not visible in all images. So as a workaround - the approach should be tested for each image.
And keep in mind that when the image does not have extreme colors like the pumpkin, the result
of assuming sRGB when the image is really Adobe RGB may be the unnecessarily washed out
result as shown in the first example.
2. Although it is not readily apparent in the examples, the problem does not lie with Adobe RGB
being inherently unsuited as a source for CMYK. The particulars of the conversion process
affect the situation and the result. The Adobe RGB to CMYK conversion can be much
improved by using newer ICC Version 4 profiles for both source and destination. ICC Version 4
profiles use an improved print-related intermediate and so can map wide gamut RGB colors
more carefully into the destination CMYK print space - using the perceptual rendering intent. So
encouraging Adobe to provide that Version 4 Adobe RGB profile will help the Adobe RGB to
CMYK situation in the long run.
3. When converting any RGB to CMYK care should be taken in selecting the CMYK profile. It is
advisable to inquire of the printer what CMYK profile should be used. Each CMYK profile matches
one particular printing condition, comprised of press, paper, screening, etc. If the photographer
converts to a CMYK that is intended for a printing condition that quite different from the actual one,
then that may cause some unexpected result in the printing.
Best regards,
Ann McCarthy
ICC Workflow WG
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