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A Typical Color-Matching Scenario

On the PC, Photoshop CS devotes three features to color management; Mac users now have only two. Formerly a standard component of Photoshop on both platforms, the Adobe Gamma control panel, which characterizes your monitor, is now a PC-only utility accessible in the Control Panel. Mac users can use the built-in Display Calibrator Assistant, available from the Color section of the Displays system preferences.

The second color management feature, common to both platforms, is the Color Settings command, found under the Edit menu on the PC and under the Photoshop menu on the Mac. Choose the command or press Ctrl+Shift+K (z -Shift-K on the Mac) to display the Color Settings dialog box, which lets you edit device-dependent color spaces and decide what to do with profile mismatches. Finally, use File Save As to decide whether to embed a profile into a saved image or include no profile at all.

I could explain each of these features independently and leave it up to you to put them together. But peering into every tree is not always the best way to understand the forest. So rather than explaining so much as a single option, I begin our tour of color management by showing the various control panels, commands, and options in action. In this introductory scenario, I take an RGB image I've created on the Mac and open it up on my PC. The Mac is equipped with a high-end prepress monitor and the PC is hooked up to a generic Sony Trinitron screen, so I have both extremes pretty well covered. Yet despite the change of platforms and the even more dramatic change in monitors, Photoshop maintains a high degree of consistency, so the image looks the same on both sides of the divide. The specifics of setting up your system will obviously vary, but this walk-through should give you an idea of how color management in Photoshop works.

Setting up the source monitor

If you own a monitor with calibration capabilities, I recommend that you start off by calibrating it. To share some common ground here, I'm going to calibrate mine using OS X's built-in Display Calibrator Assistant. As I mentioned a few paragraphs ago, you can access this by clicking the Calibrate button in the Color panel of the Displays system preferences, as shown in Figure 16-1. The Display Calibrator Assistant utilizes ColorSync, which is Apple's system-wide color management system.

Figure 16-1: On the Mac, clicking the Calibrate button on the Color panel of the Displays system preferences launches the Display Calibrator Assistant.

The Macintosh Display Calibrator Assistant

After I've fired up the Display Calibrator Assistant, I'll go ahead and flatter myself by turning on the Expert Mode check box. That gives me access to a few more options. If you're following along at home, you may find that you can't access every option in the Display Calibrator Assistant, or for that matter of the Adobe Gamma control panel on the PC. Some monitors, particularly LCD displays, don't allow for every adjustment. You navigate through the Display Calibrator Assistant by clicking the buttons in the lower-right corner of the window. Often, the first step is adjusting the gamma control. Although you'll probably want to keep this on the Mac Standard default, it can be very enlightening to slide the control down to the PC Standard to see just how much darker PC screens generally are. This is an important thing to remember when designing graphics for the Web. Through the other stages of this process, you can fine-tune the brightness levels on your monitor by adjusting the luminance response curves. Most importantly, you can set the white point of your display, which balances the red, green, and blue display functions of your monitor. After being asked to name the profile, I'm finished. I can see in the Displays system preferences that the ColorSync display I just created is now assigned to the monitor.

The Adobe Gamma control panel

For the PC users among you, Photoshop ships with the Adobe Gamma control panel. Under Windows systems before XP, choose Settings from the Start menu, and then choose Control Panel. After the Control Panel window appears, double-click the Adobe Gamma icon. (Make sure you're viewing all Control Panel options.) Under Windows XP, the Control Panel is available immediately under the Start menu. If you don't see the Adobe Gamma icon, click the Appearance and Themes option, and then double-click the Adobe Gamma icon. (If the control panel displays a warning that your video card doesn't support system-wide color management, don't sweat it. Most video cards don't.) Select the Step By Step (Wizard) option and click the Next button to walk through the setup process one step at a time. If you see a control panel like the one on the right side of Figure 16-2, click the Wizard button to continue.

Figure 16-2: Select the Step By Step option (left) to advance one step at a time through the otherwise imposing Adobe Gamma options (right).

When using the Adobe Gamma Wizard, all you have to do is answer questions and click the Next button to advance from one screen to another. For example, after adjusting the contrast and brightness settings, Gamma asks you to specify the nature of your screen's red, green, and blue phosphors. If you own a Trinitron or Diamondtron monitor — which you'll know because you paid more for it — select the Trinitron settings. Or select Custom and enter values according to your monitor's documentation. If the documentation does not suggest settings, ignore this screen and click Next to move on. So you don't know your phosphors — that's life. You have bigger fish to fry.

As with the Native Gamma section of the Mac Display Calibrator Assistant, the next screen, pictured in Figure 16-3, is the most important. It asks you to balance the red, green, and blue display functions of your monitor. But to do so, you need to turn off the View Single Gamma Only check box; this presents you with separate controls over each of the three monitor channels. Then use the sliders to make the inner squares match the outer borders. You are in essence calibrating the monitor according to your unique perceptions of it, making this particular brand of characterization a highly personal one.

Figure 16-3: Turn off the View Single Gamma Only check box to modify each of the three color channels independently.

The next screen asks you to set the white point, which defines the general color cast of your screen from 5,000 degrees Kelvin for slightly red to 9,300 degrees for slightly blue. A medium value of 6,500 degrees is a happy "daylight" medium. To find the best setting for your monitor, click the Measure button. Then click the gray box that appears the most neutral — neither too warm nor too cool — until you get dumped back into the Gamma Wizard. Then click Next.

After you click the Finish button, the Gamma utility asks you to name your new monitor profile and save it to disk. Name it whatever you want, but don't change the location — the profile has to stay in the default location to be made available to Photoshop and other applications.

Adobe Gamma generates a custom monitor profile and automatically alerts Photoshop to the change. Your screen may not look any different than it did before you opened Gamma, but you can rest assured that Photoshop is now officially aware of its capabilities and limitations.

Selecting the ideal working space

Now that I've identified my monitor, I need to select an RGB working environment, which is a color space other than the one identified for the monitor. This is the strangest step, but it's one of the most important as well. Fortunately, all it requires is a bit of imagination to understand fully.

On my Mac, I switch to Photoshop and choose Photoshop Color Settings. Photoshop displays the dialog box shown in Figure 16-4. I'm immediately faced with a dizzying array of options — no gradual immersion into the world of color management here — but Photoshop does make a small attempt to simplify the process. The program offers several collections of predefined settings under the Settings pop-up menu. Among the settings are Color Management Off, which deactivates Photoshop's color management entirely; ColorSync Workflow, which is useful in all-Macintosh environments; and Emulate Photoshop 4, which both turns color management off and mimics Version 4's screen display. Adobe has even added a few new settings to the already daunting list in Photoshop CS. Mostly, these let you assign a working space that's standard for Adobe products in either Europe, Japan, or North America.

Figure 16-4: I choose U.S. Prepress Defaults to access the Adobe RGB (1998) color space, which affords me a large theoretical RGB spectrum.

Each of these options has its relative advantages in certain settings, but most folks will want to gravitate toward two other options. If you create most of your images for the Web, select the Web Graphics Defaults option. This directs Photoshop's color functions so that they're most amenable to screen display. On the other hand, if most of your artwork finds its way into print, and if you live in the United States or a country that supports U.S. printing standards, select U.S. Prepress Defaults.

For my part, I select U.S. Prepress Defaults, as shown in Figure 16-4. If you have any doubts about whether to favor Web or print graphics, I recommend you do the same. Why? Among its other attractions, the U.S. Prepress Defaults option sets the working RGB color space to Adobe RGB (1998), arguably the best environment for viewing 24-bit images on screen.

Adobe RGB includes a wide range of theoretical RGB colors, whether they can truly be displayed on a monitor or not. You may see some clipping — where two or more color spaces appear as one — on screen, but Photoshop has greater latitude when interpolating and calculating colors.

After selecting U.S. Prepress Defaults, I click the OK button. The source environment is fully prepared. Now to save an image and send it on its way.

Embedding the profile

The final step on the Mac side is to embed the Adobe RGB profile into a test image. (The word embed simply means that Photoshop adds a little bit of code to the file stating where it was last edited.) For this, I choose File Save As, which displays the dialog box in Figure 16-5. After naming the file and specifying a location on disk, I select the Embed Color Profile check box, which embeds the Adobe RGB color profile into the test image. Then I click the Save button to save the file.

Figure 16-5: I select the Embed Color Profile check box to append the Adobe RGB profile to the image saved on the Mac.

Setting up the destination space

After saving the test image with the embedded Adobe RGB profile, I e-mail it from my Mac to my PC. No translation occurs here; this is a simple file copy from one computer to another. Now before I can open this image and display it properly on my PC, I have to set up my RGB colors. I start by characterizing my monitor. This time I'm on the PC, so I perform the calibration using the Adobe Gamma Wizard, as discussed previously in the section "The Adobe Gamma control panel."

After I finish with Adobe Gamma, I go into Photoshop and choose Edit Color Settings or press Ctrl+Shift+K. Now if I were really trying to calibrate my systems to match up, I would select U.S. Prepress Defaults from the Settings pop-up menu, just as I did on the Mac. But for purposes of this demonstration, I want to force Photoshop to perform a conversion, and a good conversion requires a little dissension. So this time around, I put on my Web artist cap and choose Web Graphics Defaults from the Settings option, as shown in Figure 16-6. This sets the RGB Working Spaces pop-up menu to the utterly indecipherable sRGB IEC61966-2.1.

Figure 16-6: On the Windows side, I select Web Graphics Defaults to set my working environment to sRGB. This forces Photoshop to make a conversion.

The truncated name for this working space is sRGB, short for standard RGB, the ubiquitous monitor space touted by Hewlett-Packard, Microsoft, and a host of others. Although much smaller and drabber than Adobe RGB, the sRGB space is perfect for Web graphics because it represents the colors projected by a run-of-the-mill PC monitor. It also happens to be Photoshop's default setting. Given that many users will never visit this dialog box, sRGB is fast becoming a cross-platform standard.

Defining color management policies

The Color Settings command determines not only how Photoshop projects images on screen but also how it reads embedded profiles. The three Color Management Policies pop-up menus control how Photoshop reacts when it tries to open an image whose embedded profiles don't match the active color settings. When Web Graphics Defaults is active, the RGB pop-up menu is set to Off, which tells Photoshop to resist managing colors when it opens an RGB image. Personally, I'm not a big fan of disabling color management entirely, especially when it threatens to ruin my color-conversion scenario. So I set the option to Convert to Working RGB, as shown in Figure 16-7.

Figure 16-7: Set the first of the Color Management Policies to Convert to Working RGB to convert the image from the Adobe RGB working space to the sRGB space.

Finally, Photoshop wants to know how it should behave when it encounters an image garnishing a profile other than sRGB. Should it convert all colors in the image to the sRGB environment? Or should it ask permission before proceeding? Personally, I like my software to be subservient, so I select Ask When Opening from the Profile Mismatches options, as in Figure 16-7.

Converting the color space

Now I'm ready to open the test image. I choose File Open just as I normally would. As Photoshop for Windows opens the test image, it detects the embedded Adobe RGB profile and determines that it does not match the active sRGB profile. Justly troubled by this development, Photoshop displays the alert box shown in Figure 16-8. You can select from three conversion options:

Figure 16-8: The alert box gives you the option of converting the colors from the foreign image or opening the image as is.

Use the embedded profile: Photoshop is perfectly capable of displaying multiple images at a time, each in a different color space. Select this option to tell Photoshop to use the Adobe RGB space instead of sRGB to display the image it's about to open. No colors are converted in the process.

Convert document's colors to the working space: This option converts the colors from the Adobe RGB space to sRGB. Because I selected Convert to Working RGB in the preceding section, this option is selected by default. Had I not selected the Ask When Opening check box, Photoshop would have performed the conversion without asking me.

Discard the embedded profile: Select this option to ignore the embedded profile and to display the image in the sRGB space without any color manipulations. Thanks to the low saturation inherent in sRGB, the result would be a significantly grayer, gloomier image.

I select the Convert Document's Colors to the Working Space radio button and click OK. Photoshop spends a few seconds converting all pixels in the image from Adobe RGB to the smaller sRGB and then displays the converted image on screen. The result is an almost perfect match — much better than the sort of results you could achieve without profile-based color management.