Re: [EXTERNAL] [PNG] Upcoming meeting topics (Fourth Edition)

On Sun, Apr 27, 2025 at 3:24 PM Leonard Rosenthol <lrosenth@adobe.com>
wrote:
> Cosmin, I can somewhat understand your position in the context of
browsers, where users are simply consuming content authored by others….but
in the case of authoring tools (e.g., Photoshop), then the considerations
are quite different and may even be business/competitive decisions.

Acknowledged -- hence my use of words "non-normative Recommendations for
Decoders". And also (perhaps even more importantly) -- *if* we can reach
consensus.

> So without really understanding what direction(s) you might be trying to
head towards – it’s difficult to offer more constructive feedback at this
time.

I will bring forth specific information, but for now, I just wanted to ask
if this can be added to our WG agenda for things to do in PNG v4.

For a sneak preview, I have no intention at all to suggest how to
interpolate or extrapolate pixel data that's been missing from the IDAT. I
was rather thinking about what to do if a PNG file ends abruptly after IDAT
but before reaching IEND. Or if a PNG file has garbage after IDAT before
reaching IEND. Or if a palette-encoded PNG file has PLTE and tRNS swapped.
All of these peculiar instances of brokenness (and a few more) have, at
least in my mind, one resolution that is rather obvious; but, please, do
let me know if I'm mistaken :-)

One last important clarification that I want to make is that I have no
plans to allow garbage data in a PNG datastream, either in the spec or in
the libpng implementation. From libpng's point of view, this is an
implementation detail. libpng has two kinds of errors: plain errors (or
just "errors", which are hard errors that trigger a hard stop), and benign
errors (which are still errors, but of a recoverable kind). So a PNG
decoder, be it libpng-based or not, can tell the application "FYI, this is
a broken PNG, but here's the data that I've been able to retrieve so far,
in case you're interested".

Sincerely,
Cosmin