Adobe 13102498 User Guide - Page 538

PHOTOSHOP CS3 531 User Guide Pixels that were fully transparent in the original image are filled with the selected color; pixels that were partially transparent in the original image are blended with the selected color. See also "Optimize an image for the web" on page 525 GIF and PNG-8 optimization options GIF is the standard format for compressing images with flat color and crisp detail, such as line art, logos, or illustrations with type. Like the GIF format, the PNG-8 format efficiently compresses solid areas of color while preserving sharp detail. PNG-8 and GIF files support 8-bit color, so they can display up to 256 colors. The process of determining which colors to use is called indexing, so images in GIF and PNG-8 formats are sometimes called indexed color images. To convert an image to indexed color, Photoshop builds a color lookup table, which stores and indexes the colors in the image. If a color in the original image does not appear in the color lookup table, the application either chooses the closest color in the table or simulates the color using a combination of available colors. In addition to the following options, you can also adjust the number of colors in the image's color table. See "Customize the color table for GIF and PNG-8 images" on page 534. 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 sensitivity. • 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.