Adobe 23101335 User Guide - Page 329

ADOBE PHOTOSHOP 6.0 319 User Guide transparency and you do not know the Web page background color, or if the background will be a pattern, you should use a format that supports transparency (GIF, PNG-8, or PNG-24). About GIF format The GIF format uses 8-bit color and efficiently compresses solid areas of color while preserving sharp detail, such as that in line art, logos, or illustrations with type. You also use the GIF format to create animated images. GIF is supported by most browsers. The GIF format uses LZW compression, which is a lossless compression method. However, because GIF files are limited to 256 colors, optimizing an original 24-bit image as an 8-bit GIF can result in the loss of color information. In addition, Photoshop and ImageReady allow you to apply lossy compression to a GIF file. Using the Lossy option yields significantly smaller files by sacrificing some image quality. GIF image with 0% dither, and with 100% dither You can reduce the number of colors in a GIF image and choose options to control the way colors dither in the application or in a browser. GIF supports background transparency and background matting, in which you blend the edges of the image with a Web page background color. About PNG-8 format The PNG-8 format uses 8-bit color. Like the GIF format, PNG-8 efficiently compresses solid areas of color while preserving sharp detail, such as that in line art, logos, or illustrations with type. Because PNG-8 is not supported by all browsers, it may be advisable to avoid this format for situations in which your image must be accessible to the widest possible Web viewing audience. For more information on browser support for PNG, see your browser's documentation. PNG-8 files use more advanced compression schemes than GIF, and can be 10-30% smaller than GIF files of the same image, depending on the image's color patterns. Although PNG-8 compression is considered lossless, optimizing an original 24-bit image as an 8-bit PNG file can result in the loss of color information. Note: With certain images, especially those with very few colors and very simple patterns, GIF compression can create a smaller file than PNG-8 compression. View optimized images in GIF and PNG-8 format to compare file size.