Re: [PNG] Cancel upcoming meeting?

Dear all,

I have updates on accessing the ISO gainmap spec (ISO 21496-1),

1) ISO/TC 42 WG 18/23 will have a ballot on having a liaison to W3C. That
ballot voting should end by the end of March 2025.

2) ISO 21496-1 is now in the DIS stage, meaning you can access the spec
publicly now (https://www.iso.org/standard/86775.html). It is at bargain
bin ISO prices, costing 65 CHF (presumably because it is considered in a
"draft" stage).

Sincerely,
Fares

On Fri, Feb 28, 2025 at 9:51 AM John Bowler <
john.cunningham.bowler@gmail.com> wrote:

> v4: cHRM chunk fix.  Entirely backward compatible; existing decoders (ones
> which actually check, which libpng no longer does) will simply reject the
> chunk (harmless since the colourspace can't be represented anyway if the
> spec is adhered to rigorousely), new decoders will handle it.
>
> Restart markers; argued about over and over again.  Fully supported at
> present but you can't do a complete parallel decode without knowing where
> the rows start and end.  That needs some information which can be cracked;
> i.e. a cracker can use it to defeat a decoder which uses the restart
> marker.  The crack is basically undetectable until all the preceding blocks
> have been decoded.  If you just want to do LZ77 "inflate" in parallel no
> biggy; doesn't require anything new.
>
> Complete parallel decode would be nice but it's so quaint and it requires
> a critical chunk.  Much much better to encode in blocks, not rows;
> much-much-much faster even though the underlying data is the same.
> Standard wisdom since the late '90s.
>
> John Bowler
>
>