Web Design in a Nutshell, 3rd Edition

When to Use PNGs

PNG is capable of supporting both indexed and Truecolor image types, so there’s no bitmapped graphic it can’t handle. Virtually all browsers in use today support PNGs as inline images, although they may not support all the bells and whistles, as you’ll see in the "Platform/Browser Support" section later in this chapter.

The PNG Story

PNG was developed in early 1995 as an effort to find a nonproprietary alternative to GIF. This was in response to the decision by Unisys to enforce its patent on LZW compression and begin collecting licensing fees from developers of GIF-supporting programs. A flurry of outrage and activity followed.

Days after the announcement, Thomas Boutell posted the first draft of the PNG specification to the comp.graphics newsgroup. A community of programmers then quickly cooperated in specifying and implementing PNG’s feature list. The key was that it used a nonpatented compression scheme, free from licensing restrictions.

The PNG format became an official W3C Recommendation in October of 1996 and updated to a second edition in 2003 (see http://www.w3.org/Graphics/PNG/). It is now also an International Standard (ISO/IEC 15948:2003). Unfortunately, with lagging browser and image editing tool support, PNG has not yet come close to replacing GIF as the primary web graphics format.

For web design purposes, there are a few criteria to consider for choosing PNG over another format for an image.