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
(http://www.acorn.com/browser) indicates that development ``will
continue...as a `spare time' activity.''