Adobe Photoshop CS5 for Photographers - Martin Evening [284]
Working with Grayscale
Grayscale image files can also be managed via the Color Settings dialog. The color management policy can be set to either ‘Preserve Embedded Profiles’ or ‘Convert to Working Gray’. If the profile of the incoming grayscale file does not match the current Gray workspace (and the Ask When Opening box is checked), you will be asked whether you wish to use the tagged grayscale space profile, or convert to the current Gray workspace.
If you examine the Gray workspace options, you will see a list of dot gain percentages and display gamma values. For prepress work you should select the dot gain percentage that most closely matches the anticipated dot gain of the press. It is important to note that the Gray workspace setting is independent of the CMYK workspace. If you want the Gray workspace dot gain value to match the black plate of the current CMYK setting, then mouse down on the Gray setting and choose ‘Load Gray…’. Now go to the Profiles folder, which will be in the Library/Application Support/ Adobe/Color/Settings folder on a Mac and in the Program Files/ Common Files/Adobe/Color/Settings folder on a PC. Select the same CMYK space as you are using for the CMYK color separations and click the Load… button. This loads the black plate dot gain value and sets it as the new Gray workspace setting. This means that when you convert images to the current Gray workspace, they will do so using the correct black plate dot gain setting to match the current CMYK setting.
If you are using grayscale mode to make prints via the Advanced B&W print options for an Epson printer, you should make sure that the Grayscale workspace uses a gamma setting that matches the gamma of your current RGB workspace. This ensures there is no gamma compensation when you convert from RGB to Grayscale (see sidebar: Matching grayscale gamma)
If you are preparing grayscale images for screen display use, such as on a website or in a multimedia presentation, then you will want to select ‘Gray Gamma 2.2’ (see the sidebar: Grayscale for screen display). If you want to know what existing prepress grayscale images will look like on the Web in grayscale mode, I suggest you select the View Proof Setup and choose Windows RGB or Macintosh RGB. You can then select Image Adjust Levels and adjust the Gamma slider accordingly to obtain the right brightness for a typical PC or Mac display (to be honest, most Mac users these days are using the same display gamma as PC users).
Advanced Color Settings
The advanced settings are normally hidden, but if you click on the More Options button, you'll see the expanded Color Settings dialog shown in Figure 12.31. These advanced settings unleash full control over the Photoshop color management system. However, don't attempt to adjust any of these expert settings until you have fully understood the intricacies of customizing the RGB, CMYK, Gray and Spot color spaces. I suggest you read through the remaining section of this chapter first before you consider customizing any of these settings.
Figure 12.31 This shows the Photoshop Advanced Color Settings dialog. Clicking on the More Options button (circled) unleashes full control over all the Photoshop settings. The following sections of this chapter show how you can customize the color management settings in the Advanced mode. Note that the button in this Color Settings dialog view normally says ‘Fewer Options’; I edited the screen shot to say ‘More Options’, simply to make it more obvious where you should click.
Custom Gray space settings
When the ‘Advanced Color Settings’ option is checked you can enter a custom gamma value or dot gain curve setting (see ‘Dot gain’ on page 667).
Scene-referred profiles
Photoshop CS4 and CS5 contain a new advanced preference called ‘Compensate for Scene-referred Profiles’. This isn't of any real significance for photographers. It is switched on