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

Acorn Browse

At the other end of the popularity spectrum--at least to judge by overall statistics--lies a browser unique in its stellar support for PNG features: Acorn Browse. Available only for Acorn computers running RISC OS, Browse has always supported PNG and has offered full gamma and alpha-transparency support since version 1.25. Not only that, but (take a deep breath now) it actually supports full alpha transparency while doing replicating (blocky) progressive display of interlaced PNGs on top of arbitrary backgrounds. That's quite a mouthful, but in simple terms it means that the browser can display, in a very elegant manner, transparent, interlaced PNGs as they download. From a programmer's perspective it's even more impressive: consider that an opaque pixel from an early interlacing pass may get replicated and thereby hide background pixels that, due to transparency, should be visible when the image is completely displayed. So extra work is necessary to ensure that parts of the background covered up by early interlacing passes are still available for compositing during later passes. As of early 1999, there was no web browser in the world with better PNG support than Browse. Unfortunately, most development on Browse itself ended late in 1998, as a result of restructuring at Acorn; version 2.07 is the latest and possibly the final release, although the web page ( indicates that development ``will a `spare time' activity.''

Last Update: 2010-Nov-26