Adobe photoshop cs2 User Manual
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Chapter 9: Color
Color modes
Color modes
Photoshop lets you choose a color mode for each document. The color mode determines what color method is used
to display and print the image you’re working on. By selecting a particular color mode, you are choosing to work with
particular color model (a numerical method for describing color). Photoshop bases its color modes on the color
models that are useful for images used in publishing. You can choose from RGB (Red, Green, Blue), CMYK (Cyan,
Magenta, Yellow, Black), Lab Color (based on CIE L* a* b*), and Grayscale. Photoshop also includes modes for
specialized color output such as Indexed Color and Duotone. Color modes determine the number of colors, the
number of channels, and the file size of an image. Choosing a color mode also determines which tools and file
formats are available.
to display and print the image you’re working on. By selecting a particular color mode, you are choosing to work with
particular color model (a numerical method for describing color). Photoshop bases its color modes on the color
models that are useful for images used in publishing. You can choose from RGB (Red, Green, Blue), CMYK (Cyan,
Magenta, Yellow, Black), Lab Color (based on CIE L* a* b*), and Grayscale. Photoshop also includes modes for
specialized color output such as Indexed Color and Duotone. Color modes determine the number of colors, the
number of channels, and the file size of an image. Choosing a color mode also determines which tools and file
formats are available.
Note: ImageReady only uses the RGB mode to work with images, because its documents are primarily intended for web
display.
display.
RGB Color mode
Photoshop’s RGB Color mode uses the RGB model, assigning an intensity value to each pixel. In 8-bits-per-channel
images, the intensity values range from 0 (black) to 255 (white) for each of the RGB (red, green, blue) components
in a color image. For example, a bright red color might have an R value of 246, a G value of 20, and a B value of 50.
When the values of all three components are equal, the result is a shade of neutral gray. When the values of all compo
nents are 255, the result is pure white; when the values are 0, pure black.
images, the intensity values range from 0 (black) to 255 (white) for each of the RGB (red, green, blue) components
in a color image. For example, a bright red color might have an R value of 246, a G value of 20, and a B value of 50.
When the values of all three components are equal, the result is a shade of neutral gray. When the values of all compo
nents are 255, the result is pure white; when the values are 0, pure black.
RGB images use three colors, or channels, to reproduce colors on-screen. In 8-bits-per-channel images, the three
channels translate to 24 (8 bits x 3 channels) bits of color information per pixel. With 24-bit images, up to 16.7 million
colors can be reproduced. With 48-bit (16-bits-per-channel) and 96-bit (32-bits-per-channel) images, even more
colors can be reproduced. In addition to being the default mode for new Photoshop images, the RGB model is used
by computer monitors to display colors. This means that when working in color modes other than RGB, such as
CMYK, Photoshop interpolates the CMYK image to RGB for display on-screen.
channels translate to 24 (8 bits x 3 channels) bits of color information per pixel. With 24-bit images, up to 16.7 million
colors can be reproduced. With 48-bit (16-bits-per-channel) and 96-bit (32-bits-per-channel) images, even more
colors can be reproduced. In addition to being the default mode for new Photoshop images, the RGB model is used
by computer monitors to display colors. This means that when working in color modes other than RGB, such as
CMYK, Photoshop interpolates the CMYK image to RGB for display on-screen.
Although RGB is a standard color model, the exact range of colors represented can vary, depending on the appli
cation or display device. Photoshop’s RGB Color mode varies according to the working space setting that you specify
in the Color Settings dialog box.
cation or display device. Photoshop’s RGB Color mode varies according to the working space setting that you specify
in the Color Settings dialog box.
Note: ImageReady uses only the RGB mode to work with images.
See also
CMYK Color mode
In the CMYK mode, each pixel is assigned a percentage value for each of the process inks. The lightest (highlight)
colors are assigned small percentages of process ink colors; the darker (shadow) colors higher percentages. For
example, a bright red might contain 2% cyan, 93% magenta, 90% yellow, and 0% black. In CMYK images, pure white
is generated when all four components have values of 0%.
colors are assigned small percentages of process ink colors; the darker (shadow) colors higher percentages. For
example, a bright red might contain 2% cyan, 93% magenta, 90% yellow, and 0% black. In CMYK images, pure white
is generated when all four components have values of 0%.