Adobe PHOTOSHOP 5.0 User Manual page 327

4 Specify a color palette:
For Palette, choose Exact to create a palette using
•
the colors in the image. This option is visible
(Windows) or not dimmed (Mac OS) only if the
image contains 256 or fewer colors.
For Palette, choose Adaptive to create a palette
•
using a representative sample of colors in the
image. (This gives the best image quality if Exact is
unavailable.) Then choose or enter the least
number of colors that retains the necessary detail
in your image.
The effect on file size of reducing the number of
colors varies depending on dimensions and color
content. For small-sized images, the effect on file
size is insignificant.
For Palette, choose System to create a palette
•
using the computer's built-in color palette. Then
select Use Best Match. The System palette option
may produce unexpected results when the image is
displayed on an 8-bit monitor using a different
built-in palette.
To use a custom palette, click Load, locate and
•
select a custom palette, and click OK. Then select
Use Best Match.
5 To view the color palette and see how the image
will appear in the Web browser, click Preview.
To navigate the preview, use the hand tool and
zoom tool provided in the preview area. These
tools have the same behavior and shortcuts as the
hand and zoom tools in the toolbox (see "Viewing
images" on page 33). Click OK to close the preview
window.
6 If dissatisfied with the results, hold down Alt
(Windows) or Option (Mac OS), and click Reset to
restore the colors in the image. Repeat steps 4 and
5 as needed.
7 To display the image gradually in increasing
detail as it is downloaded, select Interlaced.
8 If the file contains a caption that you want to
include as a comment in the GIF header, select
Export Caption. (See "Adding file information" on
page 313.)
9 Click OK. Choose a location for the exported
file, and click Save.
Exporting indexed-color images to GIF
When you export an indexed-color image to GIF,
you can assign background transparency to areas
in the image. All areas containing the colors you
specify are recognized as transparency by Web
browsers.
For finer control, you may want to define
background transparency using an alpha channel
mask instead of assigning transparency to colored
areas. For example, you may want to assign
background transparency to only part of a colored
area, keeping the other part visible on the Web
page. See Chapter 10, "Using Channels and
Masks," for more information on alpha channels.
Note: To reduce the number of colors in an indexed-
color image, convert the image to RGB mode, and
then export the image to GIF using the Exact palette
option.
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User Guide