Color Gamuts - Adobe PHOTOSHOP 5.0 User Manual

66 CHAPTER 4
Choosing a Color Mode
Duotone mode
tritone (three-color), and quadtone (four-color)
grayscale images using two to four colored inks.
(See "Using monotones, duotones, tritones, and
quadtones" on page 339.)
Indexed color mode
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 simulates the
color using available colors.
By limiting the palette of colors, indexed color can
reduce file size while maintaining visual quality—
for example, for a multimedia animation appli-
cation or a Web page. Limited editing is available
in this mode. For extensive editing you should
convert temporarily to RGB mode. (See
"Converting to indexed color" on page 72.)
Multichannel mode
multiple channel. Multichannel images are useful
for specialized printing—for example, converting
a duotone for printing in Scitex CT format.
These guidelines apply to converting images to
Multichannel mode:
You can convert any image composed of more
•
than one channel to a multichannel image. The
original channels are converted to spot color
channels.
When converting a color image to multichannel,
•
the new grayscale information is based on the
color values of the pixels in each channel.
Creates duotone (two-color),
Uses at most 256 colors. When
Uses 256 levels of gray in each
Converting a CMYK image to multichannel
•
creates cyan, magenta, yellow, and black spot
channels.
Converting an RGB image to multichannel
•
creates cyan, magenta, and yellow spot channels.
Deleting a channel from an RGB, a CMYK, or a
•
Lab image automatically converts the image to
multichannel mode. See "Color channels" on
page 67 for more information on channels.
Note: You cannot print a color composite from
Multichannel mode. Also, most export file formats
do not support multichannel mode images.
However, you can export the file in Photoshop
DCS 2.0 format.
For a color illustration of the effect of color
modes on file size, see the figure
on page 229.

Color gamuts

A gamut is the range of colors that a color system
can display or print. The spectrum of colors seen
by the human eye is wider than the gamut available
in any color model.
Among the color models used in Photoshop,
L*a*b has the largest gamut, encompassing all
colors in the RGB and CMYK gamuts. Typically,
the RGB gamut contains the subset of these colors
that can be viewed on a computer or television
monitor (which emits red, green, and blue light).