“PNG is extensible. PNG is lossless. PNG is a single-image,
raster (bitmap) format. One of its overriding design goals was
backward compatibility. As a result, don’t expect to see any sort
of lossy compression methods (JPEG is doing a fine job of that,
with the exception of transparency–but see JNG, below). Also don’t
expect to see any vector-based extensions–SVG with gzip
content-encoding has that covered. Indeed, don’t expect to see any
new, incompatible compression methods for quite a while. Until
there are lossless methods that can, on average, halve the size of
PNG images, the cost in software compatibility is far too great.
(Keep in mind that there still browsers that don’t support
progressive JPEG, and that was a relatively trivial change! And
let’s not even talk about JPEG 2000…)”
“PNG is also not going to become an animated format. Leaving
multiple-image support out of PNG was a conscious design decision
by the PNG development group, and it’s still the right decision.
Overloading a still image format with animation or video features
merely confuses users and web browsers, which have no way to
distinguish still images from animations without prying into the
data streams (which usually means downloading them first).
Developers who prefer to program monolithically can always program
for MNG instead; it’s architecturally identical to PNG, and PNG is
a pure subset of MNG.”
“Most browsers have supported PNG since at least late 1997
(when Netscape Navigator and Microsoft Internet Explorer finally
did), but almost without exception, their support for alpha
transparency has been abominable. Amazingly enough, it seems
that 2000 may be the year that browsers finally support it, more or
less ubiquitously. In April alone there were three newcomers, with
another in May; so far this year, the total has more than
doubled….”