Re: [PNG] Cancel upcoming meeting?

>
> so sleep is cancelled

RIP sleep.

It isn't a break but it is an incompatible new version

Agreed.
I expect that to be significantly more scrutinized, questioned, and tested.
I guess I should file it under "maybe".

ISO 22028-5 paywalled

Oh. That's a problem.
We need to loop back on if ITU-R BT.2408 is effectively the same (and not
paywalled).

cHRM chunk fix

Oh! Right! I forgot about that one. Thank you.
I think that is likely to get in. I tried playing devil's advocate and
pretty much everyone I spoke to wanted it. Devil's advocate was the only
pushback.

a cracker can use it to defeat a decoder which uses the restart marker

I didn't understand this. Do you mean "There is a restart marker at bit
index 200" but there isn't, so the parallel and serial decodes are
different?

 Much much better to encode in blocks

I agree. Pretty much every modern image compression I know operates on
blocks. I think we'll have a very hard time getting that into PNG though.
That would be a pretty radical change.

ISO <-> W3C liaison vote

Heyyyy nice!

ISO 21496-1 paywalled

Oh dear. I'll leave it to the liaisons to discuss this.

On Thu, Feb 27, 2025 at 8:10 PM Fares Alhassen <falhassen@google.com> wrote:

> 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
>>
>>