Simulating Spot Colors in CMYK

If you've decided to create or adjust your multitone in CMYK mode, you'll likely want to see a reasonable representation of the image on your screen. If the image is a process-color multitone, this isn't a problem at all. But if you're using one or more spot colors, Photoshop balks at the proposalit thinks only in cyan, magenta, yellow, and black.

Fortunately, you can change Photoshop's thinking by creating a custom profile with your own definitions of CMYK, by choosing Custom CMYK from the CMYK working space menu in the Color Settings dialog box. As we discussed back in Chapter 5, Color Settings, Photoshop knows what color inks you're using by the ink set you've chosen from the Ink Colors menu in the Custom CMYK dialog box.

Here's how you can change these values to simulate spot colors and get a reasonably good on-screen representation of your image.

1.	Find the Lab values for the inks you'll be printing with. (If you've already picked a Pantone or other spot color in the Duotone dialog box, click on the color swatch there. If you haven't picked one yet, you can find one by opening the Color Picker, clicking Custom, then clicking the Picker button to go back to the Color Picker.)
2.	Note the Lab values for the color. (Yes, you have to write them down.)
3.	Open Color Settings (Command-Shift-K) and choose Custom CMYK from the CMYK working space popup menu. Next, choose Custom from the Ink Colors popup menu (see Figure 10-19). Figure 10-19. CMYK Setup and Ink Colors dialog boxes
4.	Click on the cyan color swatch and type in the Lab values for the spot color you chose. (If you have precise Lab or xyY values from a spectrophotometer, you can skip clicking on the color swatch and simply turn on the Lab Coordinates checkbox.) We suggest turning on the Estimate Overprints checkbox so you don't have to specify values for C+Y, C+M, and so on; this won't guarantee that the screen color will be any better, but other than using a spectrophotometer on an ink drawdown, it's about as good as it's going to get. Click OK to save the ink settings (or, if your image is a tritone or quadtone, change those inks first), then click OK again to close the Custom CMYK dialog box. If you want to save your custom settings as an ICC profile, see "Tip: Creating ICC Profiles from Custom CMYK Settings" in Chapter 5, Color Settings.

Photoshop now thinks of cyan as the spot color. However, if your image already has an embedded profile, you'll have to select Assign Profile (from the Edit menu) and choose either "Don't Color Manage This Document" or the CMYK working space you just built. When you save this CMYK working space, your multitone images should appear correctlymore or lesson the screen.

Note that making changes in Color Settings has no effect on CMYK image data. It has a radical effect, however, on any image that you convert to CMYK mode, and on the way Photoshop displays CMYK images. Therefore, we strongly suggest you give the custom profile a name that clearly indicates that it's for use with a nonstandard ink set, and switch back to a standard SWOP ink set (or whatever you usually use) whenever you're not working on your spot-color image.