E-LEARNING- PHOTOSHOP CS4

Grayscale mode:
Black, white, and shades of gray are used to make up the “colors” in an image (no hue is present). In 8-bpc images, there can be 256 brightness values. Grayscale images’ values can be measured in a range from 0 (black) to 255 (white) or with 0 percent–100 percent of black ink coverage. Grayscale mode can be used when preparing images to be printed with one color of ink. Grayscale images can be assigned a color within most page layout software, such as InDesign or Quark Xpress.

Bitmap mode:
Only black and white pixels are used. Bitmap mode images are 1-bpc images. They are often used for simple artwork that lends itself to reproduction in only black and white pixels, sometimes called line art. Bitmap mode images can be assigned a color within most page layout software, such as InDesign or Quark Xpress.

Duotone mode: In Duotone mode, one to four custom inks can be used to make up the colors in an image. Figure 1.14 shows Duotone-mode channels, options, and curves. A dutone can be used to add a color tint to a black-ink photo printed in a brochure that uses only black ink plus one other color. A quadtone with custom inks can give a rich
and uniquely colored look to a photograph. Pantone offers reference books that show sample duotones printed in various inks and their ink percentages.

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. 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.

Multichannel mode:
Multichannel mode uses only spot channels (see Figure 1.16), channels that store parts of an image that you want to print in custom-selected inks (sometimes called spot colors), such as inks from the Pantone color library. In Multichannel mode, you can put certain parts of an image on each spot channel and assign custom-selected inks to the spot channel. For example, you can put a custom-red-ink logo on the spot channel for red ink and a custom-blue-ink background on the spot channel for blue ink. You can also put image areas that you want to print in clear varnishes on spot channels. Spot channels result in inks overprinting each other, so if the logo mentioned previously is to print in red ink only, then the area corresponding to the logo in the blue spot channel
must contain no pixels in order to avoid blue ink printing on the red ink logo.

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