File Formats in Web Graphics

You currently can use only three image file formats in the Web Site Design: GIF, JPG, and PNG. These formats all compress images to create smaller files. Knowing which file format to use for which type of images is important. If you choose the wrong file type, your image will not compress or appear as you expect. Color depth (described in the “Color Basics” section of this chapter) is a factor in image file format as well. Of the three Web-based image file formats, JPG supports 24-bit color, GIF supports 8-bit color, and PNG supports both 8-bit and 24-bit color. The file format’s color depth controls the number of colors that can be displayed.

The Graphics Interchange Format (GIF) is San Francisco Web design for online delivery of graphics. GIF uses a lossless compression technique, meaning that no color information is discarded when the image is compressed.
The color depth of GIF is 8-bit, allowing a palette of no more than 256 colors. In fact, the fewer colors you use, the greater the compression, which results in smaller file size. The GIF file format excels at compressing and displaying flat color areas, making it the logical choice for line art and color graphics. Because of its limited color depth, GIF is not the best file format for photographs or more complex graphics that have gradations of color, such as shadows and feathering.

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