[PNG] Meeting minutes - Sep 29th, 2025

Attached is a PDF of the meeting minutes from Sep 29th, 2025.

Recap:

   - C2PA's 'caBX' chunk will be added, including with the public/private
   bit set to private.
      - The public/private bit meaning was previously disregarded for APNG
      because it already had widespread adoption. The same is true here. But
      going forward, the bit isn't terribly meaningful anyway so we might drop
      the meaning and leave a comment about the bit's historical meaning.
      - C2PA can contain a thumbnail, which could become out of date. This
      is similar to EXIF. And just like EXIF, this is worth pointing out as a
      security risk. A person might crop out sensitive information but the
      thumbnail would still show it, for example.
   - SMPTE ST 2094-10 (tone mapping metadata, average luminance across
   frames) will not be added. It is too specific and we do not think there is
   enough industry demand yet.
   - SMPTE ST 2094-50 (gain curves) likely will be added. But we might wait
   for more adoption/demand before we standardize it into PNG.
      - Unclear how T.35 is related.
   - ISO 21496-1 (gain maps) will be added. We should look at documentation
   from Adobe <https://helpx.adobe.com/camera-raw/using/gain-map.html>,
   Apple
   <https://developer.apple.com/documentation/appkit/applying-apple-hdr-effect-to-your-photos>,
   and Google
   <https://developer.android.com/media/platform/hdr-image-format#iso_21496_1_compatibility>'s
   implementation when forming our standard.

Our next meeting is scheduled for Oct 13th, 2025. That is a public holiday
in the US so we might cancel. I'll follow up on this later.