Color gamuts (Photoshop)

A gamut is the range of colors that a color system can display or print. The spectrum of colors seen by the human eye is wider than the gamut available in any color model.

Among the color models used in Photoshop, L*a*b has the largest gamut, encompassing all colors in the RGB and CMYK gamuts. Typically, RGB gamuts contain the subset of these colors that can be viewed on a computer or television monitor (which emits red, green, and blue light). Therefore, some colors, such as pure cyan or pure yellow, can’t be displayed accurately on a monitor.

CMYK gamuts are smaller, consisting only of colors that can be printed using process-color inks. When colors that cannot be printed are displayed on-screen, they are referred to as out-of-gamut colors—that is, outside a CMYK gamut. (See “Identifying out-of-gamut colors (Photoshop)” on page 136.)

Important: The gamut for an RGB or CMYK image depends on its document profile. (See “About color management” on page 102.)

A

B

C

Color gamuts:

A. A Lab color gamut B. An RGB color gamut C. A CMYK color gamut

Adjusting the monitor display

Although the RGB color model used by computer monitors is capable of displaying much of the visible spectrum, the video system sending data to a given monitor often limits how many colors can be displayed at once. By understanding how color data is measured in digital files and on-screen, you can better adjust color display settings to offset the limitations of your video system.

Specifying 8-bit color display (Photoshop)

When you’re working with a display system that supports 8-bit color, the monitor displays only 256 different colors at a time. As a result, Adobe Photoshop uses a technique called dithering to mix pixels of available colors and thus simulate colors not currently available.

Note: Most monitors are capable of displaying 24-bit color. To achieve the best results, avoid using 8-bit display mode when editing color images.

By default, Adobe Photoshop uses pattern dithering, which can result in a distinctive pattern of darker or lighter areas in the image. In contrast, diffusion dithering eliminates this distinctive patterning by using the surrounding pixels in the mix of pixel color. But diffusion dithering can cause visual inconsistencies when only part of a screen is redrawn as you scroll, edit, or paint. Keep in mind that dithering effects only appear on-screen, not in print.

To select a color display option:

1 Do one of the following:

• In Windows or Mac OS 9.x, choose Edit > Preferences > Display & Cursors.

• In Mac OS X, choose Photoshop > Preferences > Display & Cursors.

2 Select Use Diffusion Dither to minimize dither patterns produced by dithering.

Making previews display more quickly (Photoshop)

The Use Pixel Doubling preference option speeds up the preview of a tool or command’s effects by temporarily doubling the size of the pixels (halving the resolution) in the preview. This option has no effect on the pixels in the file; it simply provides faster previews with the tools and commands.

To speed up previews:

1 Do one of the following:

• In Windows or Mac OS 9.x, choose Edit > Preferences > Display & Cursors.

• In Mac OS X, choose Photoshop > Preferences > Display & Cursors.

2 Select Use Pixel Doubling, and click OK.

Adjusting color display for cross-platform variations

RGB color display on a computer monitor varies with the operating system used by the computer. For example, an image appears darker on a Windows system than on a Mac OS computer (because the standard RGB color space is darker in Windows than in Mac OS). The Preview commands in ImageReady enable you to compensate for cross-platform differences in RGB color display during image preview. In Photoshop, you can simulate cross-platform differences by using the Macintosh RGB, Windows RGB, and Monitor RGB commands in the View > Proof Setup menu. (See “Soft-proofing colors” on page 113.)

RGB color display can also vary between Photoshop and ImageReady. In Photoshop, you can select from several RGB color spaces when editing images. As a result, images

created in Photoshop may use an RGB color space that differs from the monitor RGB color space used by ImageReady. You can adjust the RGB color display during image preview to compensate for differences between Photoshop and ImageReady.

To adjust RGB color display for cross-platform variations (ImageReady):

Choose View > Preview and choose an option for adjusting the color display:

•Uncompensated Color (the default option) to view the image with no color adjustment.

•Standard Macintosh Color (Windows) to view the image with color adjusted to simulate a standard Macintosh monitor.

•Standard Windows Color (Mac OS) to view the image with color adjusted to simulate a standard Windows monitor.

Note: These options adjust color display only. No changes are made to pixels in the image.

To adjust RGB color display to match Photoshop color display (ImageReady):

Choose View > Preview > Use Embedded Color Profile.

Note: In order to use the Use Embedded Color Profile command in ImageReady, you must save the original image, with color profile embedded, in Photoshop.