RGB to CMYK problems

AL
Posted By
Alfred_Law
May 22, 2004
Views
346
Replies
6
Status
Closed
I was asked to change a dozen RGB photos prepared in Photoshop CS to CMYK for offset printing. When I did this, however, the two photos which were predominantly blue came out looking washed out and, in one case, off color in a way I couldn’t correct using various Photoshop tools. One thing I noticed was that the histograms of the CMYK versions were almost flat while in the RGB versions they were spikey and covered much of the graph. Is there any way to resolve this problem? The other ten photos, incidentally, looked good.
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cmyk problems rgb

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H
Ho
May 22, 2004
The success of your conversion depends on several things, such as: the colors being converted, the accuracy of the color profiles (especially for your destination space), and your rendering intent. Perceptual or Relative Colormetric are usually the best choices.

Blue in RGB can quickly run to out of gamut in the CMYK space. Were all the rest of the photos similar or did they have different backgrounds? Did they all have the same RGB working profile? What was your CMYK conversion setup? Did you check for our of gamut colors before you converted? Is your monitor profile up to date? How are you soft-proofing the converted images?

I don’t really expect you to answer all these questions, I’m just trying to give you clues and hints about where the problem may lie. If you can’t resolve it, give us a full report.
AL
Alfred_Law
May 23, 2004
Those questions, not all of which I even understand, make it quite obvious that I don’t know enough to do this process effectively. I read (and thought I understood) a number of Photoshop Help pages before starting the conversion attempt, but I clearly didn’t learn enough. Is there somewhere on line I can learn more about this process, or must I take another Photoshop workshop devoted specifically to RGB-CMYC conversion?
L
LenHewitt
May 23, 2004
Alfred,

You can learn about Colour management at http://www.computer-darkroom.com – well worth a visit.

There is also a recent topic here dealing quite extensively with colour management questions:

http://www.adobeforums.com/cgi-bin/webx?13@@.3bb3c725
H
Ho
May 23, 2004
The April/May Photoshop User Magazine has a cover story on color management that will help you. It may still be available on news stands.

Do a Google search for RGB to CMYK and see what pops up. Be prepared to spend some time sifting through. Here is one example:

" http://www.designer-info.com/master.htm?http://www.designer- info.com/Writing/rgb_to_cmyk.htm" (Remove quotes).

Finally, a quick scan of the CS User Guide reveals nothing much of value regarding RGB to CMYK conversions. I recommend Real World Photoshop, published by Peachpit Press. I’m sure the CS Version is out by now but, if not, the latest available edition will contain all the info you will need about nearly any PS related topic.
AL
Alfred_Law
May 23, 2004
Many thanks for Len and Ho!
L
LenHewitt
May 23, 2004
You’re very welcome, Alfred

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