Adobe illustrator 10 Manuale Utente
|
Back
Adobe Illustrator Help
Preparing Graphics for the Web
|
Back
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. You can lower the size of GIF images by reducing
the number of colors in the file. Like the GIF format, the PNG-8 format efficiently
compresses solid areas of color while preserving sharp detail; however, not all Web
browsers can display PNG-8 files. PNG-8 settings are very similar to the GIF settings.
(See
line art, logos, or illustrations with type. You can lower the size of GIF images by reducing
the number of colors in the file. Like the GIF format, the PNG-8 format efficiently
compresses solid areas of color while preserving sharp detail; however, not all Web
browsers can display PNG-8 files. PNG-8 settings are very similar to the GIF settings.
(See
Optimization panel for GIF format
A. File format menu B. Color Reduction Method menu C. Dithering Method menu
D. Optimize menu
A. File format menu B. Color Reduction Method menu C. Dithering Method menu
D. Optimize menu
Lossy (GIF only) Specify a Lossy 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.
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.
Dither algorithms.
Color Reduction Method and Colors Choose a method for generating a color table from
the Color Reduction Method menu. (See
the Color Reduction Method menu. (See
.) Then
specify the maximum number of colors in the Colors text box. If you choose Web for the
color reduction method, the Auto option becomes active in the Colors pop-up menu. Use
the Auto option if you want Illustrator to determine the number of colors in the color table
based on the frequency of colors in the image.
color reduction method, the Auto option becomes active in the Colors pop-up menu. Use
the Auto option if you want Illustrator to determine the number of colors in the color table
based on the frequency of colors in the image.
Note: If the image contains fewer colors than the number specified, the color table will
contain only the number of colors in the image.
contain only the number of colors in the image.
Dithering Method and Dither Choose a dithering method from the Dithering Method
menu, and specify the amount of application dithering. Dithering refers to the method of
simulating colors not available in the color display system of your computer. A higher
dithering percentage creates the appearance of more colors and more detail in an image,
but can also increase the file size. For optimal compression, use the lowest percentage of
dither that provides the color detail you require. Images with primarily solid colors may
work well with no dither. Images with continuous-tone color (especially color gradients)
may require dithering to prevent color banding. Choose No dither or select an option in
the Dithering Method menu:
menu, and specify the amount of application dithering. Dithering refers to the method of
simulating colors not available in the color display system of your computer. A higher
dithering percentage creates the appearance of more colors and more detail in an image,
but can also increase the file size. For optimal compression, use the lowest percentage of
dither that provides the color detail you require. Images with primarily solid colors may
work well with no dither. Images with continuous-tone color (especially color gradients)
may require dithering to prevent color banding. Choose No dither or select an option in
the Dithering Method menu:
•
Diffusion applies a random pattern that is usually less noticeable than Pattern dither.
The dither effects are diffused across adjacent pixels.
C
D
A
B