The PNG Guide is an eBook based on Greg Roelofs' book, originally published by O'Reilly.


Also in 1996 came the revival of efforts to produce a multiple-image variant of PNG suitable for slide shows, animations, and very efficient storage of certain simple kinds of images. Multi-image support had been left out of the PNG specification for several reasons: multi-image capability in GIF was supported by virtually no one; multi-image GIFs were indistinguishable from single-image GIFs (i.e., they had the same filename extension); including multi-image support in PNG would have delayed both its development and its acceptance in the marketplace, due to the burden of extra complexity, and creating a separate, PNG-based multi-image format not only would be a logical extension of PNG but also would be more appropriate to a group with backgrounds in animation and multimedia. As it happened, however, this latter group never materialized, and with the early-1996 release of Netscape Navigator 2.0 with support for GIF animations,[54] it became clear that the PNG Group needed to produce some sort of response.

[54] Alas, Netscape's support of GIF animations probably did more to ensure the format's longevity than any other event in GIF's history.

Unfortunately there was a fairly fundamental disagreement within the group over whether the new format should be a very thin layer on top of PNG, capable of duplicating GIF animations but not much more, or whether it should be a full-fledged multimedia format capable of synchronizing images, sound, and possibly video. Although the former would have been trivial (and fast) to design and implement, proponents of the latter design held sway during the early discussions in the summer of 1996. In the end, however, something of a compromise was created--though possibly due more to attrition than consensus. Called Multiple-image Network Graphics, the MNG format design was largely shaped by Glenn Randers-Pehrson and included simple but general operations to manipulate sections of images, but no direct sound or video support. As of November 1998 the MNG specification was close to being frozen, but was also quite large and still awaiting implementation in the form of a reference library similar to libpng. Until such time as either a reference library or some other form of complete implementation exists, the MNG spec will not be approved as a standard, nor is it likely that more than a handful of third-party developers will offer support for it.

Last Update: 2010-Nov-26