Adobe 13102498 User Guide - Page 118

PHOTOSHOP CS3 111 User Guide Lab Color mode The CIE L*a*b* color model (Lab) is based on the human perception of color. The numeric values in Lab describe all the colors that a person with normal vision sees. Because Lab describes how a color looks rather than how much of a particular colorant is needed for a device (such as a monitor, desktop printer, or digital camera) to produce colors, Lab is considered to be a device-independent color model. Color management systems use Lab as a color reference to predictably transform a color from one color space to another color space. The Lab Color mode has a lightness component (L) that can range from 0 to 100. In the Adobe Color Picker and Color palette, the a component (green-red axis) and the b component (blue-yellow axis) can range from +127 to -128. Lab images can be saved in Photoshop, Photoshop EPS, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, TIFF, Photoshop DCS 1.0, or Photoshop DCS 2.0 formats. You can save 48-bit (16-bits-per-channel) Lab images in Photoshop, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, or TIFF formats. Note: The DCS 1.0 and DCS 2.0 formats convert the file to CMYK when opened. Grayscale mode Grayscale mode uses different shades of gray in an image. In 8-bit images, there can be up to 256 shades of gray. Every pixel of a grayscale image has a brightness value ranging from 0 (black) to 255 (white). In 16 and 32-bit images, the number of shades in an image is much greater than in 8-bit images. Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white, 100% to black). Grayscale mode uses the range defined by the working space setting that you specify in the Color Settings dialog box. See also "About color working spaces" on page 146 Bitmap mode Bitmap mode uses one of two color values (black or white) to represent the pixels in an image. Images in Bitmap mode are called bitmapped 1-bit images because they have a bit depth of 1. Duotone mode Duotone mode creates monotone, duotone (two-color), tritone (three-color), and quadtone (four-color) grayscale images using one to four custom inks. See also "About duotones" on page 498 Indexed Color mode Indexed Color mode produces 8-bit image files with up to 256 colors. When converting to indexed color, Photoshop builds a color lookup table (CLUT), which stores and indexes the colors in the image. If a color in the original image does not appear in the table, the program chooses the closest one or uses dithering to simulate the color using available colors.