Datasheet

15
Working with Digital Images
1
Color mode
The color mode of an image specifies which basic set of colors is used to make up an image. You
can specify the color mode in the Image ➪ Mode menu.
Colors within most color modes are stored in color channels. You can view the channels in the
Channels palette.
The color modes available in Photoshop are:
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RGB color mode. Red, Green, and Blue are used to make up the image’s color. In 8-bpc
images, tonal values range from 0 (black) to 255 (white), for each of the three colors.
When the values for all three colors are equal, the resulting color is a neutral color —
black, white, or a shade of gray with no color hue. RGB mode (see Figure 1.9) is used to
display images on-screen because monitors use Red, Green, and Blue light to display
color. It is also commonly used when color-correcting images.
FIGURE 1.9
RGB mode channels
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CMYK color mode. Cyan, Magenta, Yellow, and Black are used to make up the image’s
color. Tonal values range from 0 percent (no color) to 100 percent (maximum amount of
color) for each of the four colors. In CMYK-colors that are neutral, Magenta and Yellow
have equal values and Cyan has a higher value than either Magenta or Yellow; the amount
of Black determines the lightness of the color.
CMYK mode (see Figure 1.10) is used when printing images with Cyan, Magenta, Yellow,
and Black inks. Typically, RGB mode is used to color-correct images in order to preserve
the maximum amount of colors and to make assigning neutral color values easier (all
three color values are equal in neutral colors in RGB mode), then the image is converted
to CMYK mode. But color correction can also take place in CMYK mode.
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Lab color mode. The Lab color mode (pronounced el, ay, bee, not lab) is based on a stan-
dardized way to describe color that corresponds to the way a person with normal vision
sees it. It is used by color management systems as an intermediate color reference to help
accurately convert colors from one color space to another. It is sometimes used in color
correction and image manipulation. Lab color (see Figure 1.11) uses the following com-
ponents to make colors: an L (lightness) component, an a component that contains green
and red, and a b component that contains blue and yellow. L values range from 0 to 100;
a and b values range from +127 to –128.