Many of Photoshop's filters are not available to images in CMYK mode. That doesn't mean you can't use the filters, it just means that you need to know a few tricks.
Here is a list of the filters unavailable in CMYK mode:
One of the simpler techniques for applying the “unavailable” filters to a CMYK image is to filter an RGB copy and add that to the CMYK image.
1. In the History palette, click the left-most button to duplicate the image.
2. Image> Mode> RGB.
3. Apply the filter to the image or to a specific layer in the image.
4. Hold down the Shift key and drag the Background layer (or the layer to which you applied the filter) from the Layers Palette to the window of the CMYK version. The Shift key ensures that the layer will be centered when copied.
The copied layer will automatically be converted to CMYK. Remember, too, that with the filter applied to a separate layer, you have a great deal of control over the appearance. You can experiment with different blending modes and opacity to change the look.
Pete
Bauer is the Help Desk Director for NAPP, as well
as a Contributing Writer for Photoshop User and Mac Design
magazines. His books include "Special Edition Using
Adobe Photoshop 7" (with Jeff Foster), "Special
Edition Using Adobe Illustrator 10," "Sams Teach
Yourself Adobe Illustrator 10 in 24 Hours" (with Mordy
Golding), and "Special Edition Using Adobe Illustrator
9." Pete writes documentation for a variety of computer
graphics related products, as well as testing software
for a number of companies. As a computer graphics efficiency
consultant, Pete specializes in customized training programs.
He is based in Columbus, Ohio, and can be contacted via
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