Adobe PHOTOSHOP 6.0 Manual page 341

To select a color reduction algorithm:
Choose an option from the Color Reduction
Algorithm pop-up menu (below the file format
menu in the Optimize panel/palette):
Creates a custom color table by giving
Perceptual
priority to colors for which the human eye has
greater sensitivity.
Creates a color table similar to the
Selective
Perceptual color table, but favoring broad areas
of color and the preservation of Web colors.
This color table usually produces images with
the greatest color integrity. Selective is the
default option.
Creates a custom color table by
Adaptive
sampling colors from the spectrum appearing
most commonly in the image. For example, an
image with only the colors green and blue
produces a color table made primarily of greens
and blues. Most images concentrate colors in
particular areas of the spectrum.
Uses the standard 216-color color table
Web
common to the Windows and Mac OS 8-bit
(256-color) palettes. This option ensures that no
browser dither is applied to colors when the image
is displayed using 8-bit color. (This palette is also
called the Web-safe palette.) If your image has
fewer colors than the total number specified in the
color palette, unused colors are removed.
Using the Web palette can create larger files, and is
recommended only when avoiding browser dither
is a high priority. See "Previewing and controlling
dithering" on page 341.
Preserves the current color table as a
Custom
fixed palette that does not update with changes to
the image.
Uses the Mac OS system's default 8-bit
Mac OS
(256-color) color table, which is based on a
uniform sampling of RGB colors. If your image
has fewer colors than the total number specified in
the color palette, unused colors are removed.
Uses the Windows system's default 8-bit
Windows
(256-color) color table, which is based on a
uniform sampling of RGB colors. If your image
has fewer colors than the total number specified in
the color palette, unused colors are removed.
Other color tables appear in the menu if you have
saved them previously. (See "Loading and saving
color tables" on page 336.)
You can use an alpha channel to influence the
generation of color tables. (See "Using channels
to modify color reduction" on page 329.)
To regenerate a color table (ImageReady):
Choose Rebuild Color Table from the Color Table
palette menu. Use this command to generate a new
color table when the Auto Regenerate option is off.
(See "Controlling optimization (ImageReady)" on
page 326.)
ADOBE PHOTOSHOP 6.0 331
User Guide