Photoshop.CS.Bible [Electronic resources] نسخه متنی

Custom CMYK Setup

To prepare an image for reproduction on a commercial offset or web press, you first need to specify how you want Photoshop to convert the image from the RGB to CMYK color space. This step also affects the conversion from CMYK to RGB, which in turn defines how CMYK images appear on screen.

You specify the CMYK space by choosing Edit Color Settings (or Photoshop Color Settings on the Mac). Then select the color profile you want to use from the CMYK pop-up menu in the Working Spaces section of the dialog box. You can select a predefined color profile, or you can define a custom CMYK conversion setup by choosing Custom CMYK from the CMYK pop-up menu. When you choose Custom, Photoshop displays the Custom CMYK dialog box, shown in Figure 16-14.

Figure 16-14: Use the options in the Custom CMYK dialog box to prepare an image for printing on a commercial offset or web press.

The following list explains each and every option in the Custom CMYK dialog box. If you're not a print professional, some of these descriptions may seem a little abstruse. After reading this section, you may want to talk with your commercial printer and find out what options, if any, he or she recommends.

Name: Okay, so this one's not so abstruse after all. Enter a name for your custom CMYK settings here.

Ink Colors: This pop-up menu offers access to a handful of common press inks and paper stocks. Select the option that most closely matches your printing environment. (Your commercial printer can easily help you with this one.) The default setting, SWOP (Coated), represents the most common press type and paper stock used in the United States for magazine and high-end display work. Regardless of which setting you choose, Photoshop automatically changes the Dot Gain value to the most suitable setting.

Dot Gain: Enter a value from –10 to 40 percent to specify the amount by which you can expect halftone cells to shrink or expand during the printing process, a variable known as dot gain. When printing to uncoated stock, for example, you can expect halftone cells to bleed into the page and expand by about 25 to 30 percent. For newsprint, it varies from 30 to 40 percent. In any case, Photoshop automatically adjusts the brightness of CMYK colors to compensate, lightening the image for high values and darkening it for low values.

Separation Type: When the densities of cyan, magenta, and yellow inks reach a certain level, they mix to form a muddy brown. The GCR (gray component replacement) option avoids this unpleasant effect by overprinting these colors with black to the extent specified with the Black Generation option. If you select the UCR (under color removal) option, Photoshop removes cyan, magenta, and yellow inks where they overlap black ink. GCR is almost always the setting of choice except when printing on newsprint.

Black Generation: Available only when the GCR option is active, the Black Generation pop-up menu determines how dark the cyan, magenta, and yellow concentrations must be before Photoshop adds black ink. Select Light to use black ink sparingly; select Heavy to apply it liberally. The None option prints no black ink whatsoever, and the Maximum option prints black ink over everything. You may want to use the UCA Amount option to restore cyan, magenta, and yellow ink if you select the Heavy or Maximum option.

Black Ink Limit: Enter the maximum amount of black ink that can be applied to the page. By default, this value is 100 percent, which is solid ink coverage. If you raise the UCA Amount value, you'll probably want to lower this value by a similar percentage to prevent the image from overdarkening.

Total Ink Limit: This value represents the maximum amount of all four inks permitted on the page. For example, assuming you use the default Black Ink Limit and Total Ink Limit values of 100 and 300 percent, respectively, the darkest printable color contains 100-percent black ink. The sum total of cyan, magenta, and yellow inks, therefore, is the difference between these values: 200 percent. A typical saturated black — a mix of inks that results in an absolute pitch-black pigment — is 70-percent cyan, 63-percent magenta, 67-percent yellow, and 100-percent black. And 70 + 63 + 67 + 100 =, you guessed it, 300.

UCA Amount: The opposite of UCR, UCA stands for under color addition, which enables you to add cyan, magenta, and yellow inks to areas where the concentration of black ink is highest. For example, a value of 20 percent raises the amount of cyan, magenta, and yellow inks applied with black concentrations between 80 and 100 percent. This option is dimmed when the UCR radio button is active.

Gray Ramp: The Gray Ramp graph on the right side of the Custom CMYK dialog box shows the effects of your changes. Four lines — one in each color — represent the four inks. Although you can't edit the colored lines in this graph by clicking and dragging them, you can observe the lines to gauge the results of your settings. If you have an urge to grab a curve and yank it, choose Custom from the Black Generation pop-up menu. The ensuing dialog box lets you edit the black curve directly while you preview its effect on the C, M, and Y curves in the background.

Saving and loading color settings

As we've seen, it can be a painstaking process of trial and error to arrive at the perfect color settings. Furthermore, the perfect settings for one job might be highly imperfect for another. Clearly, there's a pressing need for a way to save and load color settings — and just as clearly, Photoshop is the sort of obliging application to provide a way to do it.

You might logically surmise that the Load and Save buttons on the right side of the Color Settings box will come into play here — and you'd be correct. After you have your settings just the way you want them, click the Save button. You'll be prompted to save your settings in a Settings folder located deep within the bowels of your computer. (Should you ever need to find it again, here's the path: Under Windows, it's Program Files\Common Files\Adobe\Color\Settings. On the Mac, it's located in your User folder at Library\Application Support\Adobe\Color\Settings.) Clicking the Load button takes you to the same folder, where you can choose the saved settings that you want to load.

And that's not all. Not only can you save and load individual CMYK Working Spaces settings, but with the dreaded Advanced Mode activated, you can save Working Spaces files for RGB, Grayscale, and Spot color settings as well. You'll find the load and save commands under the individual pop-up menus for each space.

But what if you work with multiple commercial prepress houses? Wouldn't it be nice to be able to select different custom working spaces from the CMYK pop-up menu without having to constantly open setup files using the Load CMYK option? Yes, it would, and here's how you do it.

STEPS: Create a Profile That Appears in the CMYK Pop-up Menu

Create an ICM file. In the Color Settings dialog box, choose Save CMYK from the CMYK pop-up menu, and give the file a name ending in the .icm extension. Other than the extension, the name you give it here isn't really that important; the original name you assigned when you first created the settings with the Custom CMYK command is the name you'll see when you actually load the settings. Wait to click Save until the next step.

Save the ICM file to the Recommended folder. For Photoshop to see the CMYK profile, you have to save it to a specific folder. On the PC, the path for that folder is C:\Program Files\Common Files\Adobe\Color\Profiles\Recommended. On the Mac, start with the Library folder at the root level of your hard drive, and then go to Application Support\Adobe\Color\Profiles\Recommended. When you finally arrive inside the Recommended folder, save the ICM file.

Quit Photoshop. Regardless of which version of Photoshop you're using, quit it by choosing File Exit (File Quit on the Mac).

Launch Photoshop. By starting (or restarting) Photoshop, you force the program to load the ICM profile.

Confirm that the profile has loaded. Press Ctrl+Shift+K (z -Shift-K on the Mac) to display the Color Settings dialog box, and then click the CMYK pop-up menu in the Working Spaces area. You should see the profile you saved in the menu.