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.

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. (See Previewing and controlling dithering.)

Optimizing Images for the Web > Choosing a file format for optimization > About GIF format