Datasheet

Welcome to Adobe Photoshop CS4

Part I

The Duotone-mode images can be referred to as monotones, duotones, tritones, or quad-

tones. Their values are typically measured with 0%–100% of ink coverage. Duotone mode

is used when two, three, or four custom ink colors (other than the typical CMYK combina-

tion) are used in printing.

Duotone mode separates the overall image into multiple custom colors, and the Duotone

mode curves can be used to adjust the percentage of ink in specific areas of the tonal

range of each color.

Indexed color mode. Up to 256 colors can be used to make up the colors in an image.

Colors are stored in a color lookup table (CLUT). Indexed color images are typically used

for GIF format images destined for on-screen display (see Figure 1.15). When you save a

GIF by choosing File ➪ Save for Web & Devices, the image is automatically converted to

Index color mode.

You can generally or selectively reduce the number of colors in an indexed color image to

reduce the image’s file size, which decreases download time for Web images. In an effort

to improve an image’s appearance while at the same time using fewer colors, you can also

take advantage of dithering, the simulation of a third color by generating the appearance

of two colors being mixed together.

FIGURE 1.15

Indexed color mode channels and GIF options, including Dither options and Color Table