Web Design in a Nutshell, 3rd Edition

PNG (Portable Network Graphic)

Unlike GIF and JPEG, PNG (Portable Network Graphic) was developed specifically with the Web in mind. PNGs can support 8-bit indexed color, 16-bit grayscale, or 24-bit true color images with a lossless compression scheme, which means higher image quality and, in some cases, file sizes even smaller than their GIF counterparts. Not only that, but PNG files also have some nifty features such as built-in gamma control and variable transparency levels (which means you can have a background pattern show through a soft drop shadow).

Despite PNG being a robust file format, browsers and graphics tools were slow to fully support the format (variable transparency levels weren’t supported in Internet Explorer until Version 7). For that reason, it lags significantly behind GIF and JPEG in popularity.

See Chapter 31 for complete information on the PNG file format.