Adobe Photoshop CS4 - Manual (Page 118)

111 USING PHOTOSHOP CS4
Color fundamentals
Last updated 1/10/2010
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
panel, 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.
More Help topics
“ About color working spaces ” on page 148
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.
More Help topics
“ About duotones ” on page 494
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.