Web Design in a Nutshell, 3rd Edition

Embedded Text

PNGs also have the ability to store strings of text . This is useful in permanently attaching text to an image, such as copyright information or a description of what is in the image. The only tools that allow text annotations to PNG graphics are Corel Paint Shop Pro and the GIMP (a free image editor for the X Window System on Unix). Fireworks will preserve embedded text information in PNGs. Ideally, the meta-information in the PNG could be accessible via right-clicking on the graphic in a browser window, but this feature is not implemented in current browsers.

PNGs in Motion

One of the only features PNG is missing is the ability to store multiple images for animation . The first effort to add motion to PNGs was the MNG format (Multiple-image Network Graphic). It gained some browser support, but its popularity suffered from the fact that MNGs were not backward compatible with PNGs. If a browser didn’t support MNG, it would display a broken graphic.

More recently, there has been a proposed extension to PNG called APNG (Animated Portable Network Graphic) that addresses the issue of backward compatibility. If a browser does not support an APNG, it displays the first frame as a static image PNG instead.

Both of these formats are in development and are not well supported as of this writing.