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Web Style Guide

PNG graphics

Portable Network Graphic (PNG, pronounced "ping") is an image format developed by a consortium of graphic software developers as a nonproprietary alternative to the GIF image format. As mentioned earlier, CompuServe developed the GIF format, and GIF uses the proprietary LZW compression scheme owned by Unisys Corporation. Any graphics tool developer who makes software that saves in GIF format must pay a royalty to Unisys and CompuServe.

PNG graphics were designed specifically for use on Web pages, and they offer a range of attractive features that should eventually make PNG the most common graphic format. These features include a full range of color depths, support for sophisticated image transparency, better interlacing, and automatic corrections for display monitor gamma. PNG images can also hold a short text description of the image's content, which allows Internet search engines to search for images based on these embedded text descriptions. Unfortunately, the PNG graphic format is not yet widely supported, and the current implementation of PNG graphics in the major Web browsers does not fully support all of PNG's features. This should change over the next few years, but do not make a commitment to PNG graphics until you are sure that most of your audience is using browsers that support PNG.