Re: [PNG] Cancel upcoming meeting?

Yeah but the PNG spec aims to be free. If it depends on a non-free
standard, that is problematic.
We can get access. But to use it, we'll need everyone to get free access.

Or at least, that is my understanding. I'll defer to liaisons.

On Thu, Feb 27, 2025 at 8:30 PM Fares Alhassen <falhassen@google.com> wrote:

> > ISO 21496-1 paywalled
> The paywall is only if you want access now. Once we have the liaison set
> up, we should be able to share relevant ISO TC/42 WG 18 specs in confidence
> with W3C members to help with development of PNG.
>
> Sincerely,
> Fares
>
> On Fri, Feb 28, 2025 at 10:25 AM Chris Blume (ProgramMax) <
> programmax@gmail.com> wrote:
>
>> 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
>>>>
>>>>