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ADOBE PHOTOSHOP CS2
User Guide
Pattern
Applies a halftone-like square pattern to determine the value of pixels.
Noise
Applies a random pattern similar to the Diffusion dithering, but without diffusing the pattern across adjacent
pixels. No seams appear with the Noise algorithm.
See also
“Using the Save For Web dialog box” on page 625
“To optimize an image for the web” on page 628
Optimization options for GIF and PNG-8 formats
In addition to the following options, you can also adjust the number of colors in the image’s color table. See “Custom
izing the color table for GIF and PNG-8 images” on page 638.
D
A
B
C
Optimization settings for GIF
A.
File Format menu
B.
Color Reduction Algorithm menu
C.
Dithering Algorithm menu
D.
Optimize menu
Lossy (GIF only)
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. The
Lossy option can reduce file size by 5% to 40%.
Note:
You cannot use the Lossy option with the Interlaced option or with Noise or Pattern Dither algorithms.
Color Reduction Method and Colors
Specifies a method for generating the color lookup table and the number of
colors you want in the color lookup table. You can select one of the following color reduction methods:
•
Perceptual
Creates a custom color table by giving priority to colors for which the human eye has greater sensi
tivity.
•
Selective
Creates a color table similar to the 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.
•
Adaptive
Creates a custom color table by sampling colors from the predominant spectrum 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.
•
(Restrictive) Web
Uses the standard 216-color color table 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.) Using the web palette can create larger files, and is recommended
only when avoiding browser dither is a high priority.
•
Custom
Uses a color palette that is created or modified by the user. If you open an existing GIF or PNG-8 file, it
will have a custom color palette.