Adobe PHOTOSHOP 6.0 Manual page 333

Setting optimization options for GIF and
PNG-8 formats
GIF is the standard format for compressing images
with flat color and crisp detail, such as line art,
logos, or illustrations with type. (See "About GIF
format" on page 319.) Like the GIF format, PNG-8
efficiently compresses solid areas of color while
preserving sharp detail; however, not all Web
browsers can display PNG-8 files. (See "About
PNG-8 format" on page 319.)
A
B
C
ImageReady Optimize palette GIF options,
with hidden options shown:
A. File Format menu B. Color Reduction
Algorithm menu C. Dither Algorithm menu
In ImageReady, you can control which options
show in the Optimize palette by clicking the Show
Options control ( ) on the Optimize palette tab.
To show all options, choose Show Options from
the Optimize palette menu.
To optimize an image in GIF or PNG-8 format:
Select a view in which to apply the
1
optimization setting.
Select the slice or slices to which you want to
2
apply the optimization setting. (See "Selecting
slices" on page 276.)
In the Optimize panel/palette, choose GIF
3
or PNG-8 from the File Format menu.
For GIF format only: Drag the Lossy slider or
4
enter a value to allow for lossy compression. Lossy
compression reduces file size by selectively
discarding data—a higher Lossy setting results in
more data being discarded.
You can often apply a Lossy value of 5–10, and
sometimes up to 50, without degrading the image.
File size can often be reduced 5%–40% using the
Lossy option.
Note: You cannot use the Lossy option with the
Interlaced option, or with Noise or Pattern
Dither algorithms.
For GIF format only: To vary the Lossy setting
5
across the selected slices using an alpha channel,
click the channel button ( ) next to the Lossy text
box. In the Modify Lossiness Setting dialog box,
choose an alpha channel from the pop-up menu,
set a lossiness range, and click OK. (See "Using
channels to modify GIF lossiness" on page 328.)
Select a color reduction algorithm.
6
(See "Generating a color table" on page 330.)
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