Re: XMP in PNG

Perfect. :D
I think we have a path forward for XMP in PNG and a clear use case for it.

That leaves the tone mapping metadata unresolved though.
Since it would likely be a new chunk and could strongly benefit from Dolby
participation, should we shelf that for now?

On Tue, Nov 30, 2021 at 5:25 PM Leonard Rosenthol <lrosenth@adobe.com>
wrote:

> As Chris said, XMP in PNG has been around for at least 15 years and is
> implemented by all major image processing tools (commercial and open
> source, from ImageMagick to GIMP) and search engines (both desktop and web).
>
>
>
> Leonard
>
>
>
> *From: *Chris Lilley <chris@w3.org>
> *Date: *Tuesday, November 30, 2021 at 5:15 PM
> *To: *Chris Blume (ProgramMax) <programmax@gmail.com>, Leonard Rosenthol <
> lrosenth@adobe.com>
> *Cc: *public-png@w3.org <public-png@w3.org>
> *Subject: *Re: XMP in PNG
>
>
> On 2021-11-30 23:43, Chris Blume (ProgramMax) wrote:
> > it sounds like this tone mapping metadata perhaps shouldn't be in XMP
> > anyway. I think we might want to create a new chunk for it so we can
> > place datastream position requirements on the chunk. It should go
> > before the frame it affects.
> Yes, that sounds reasonable.
> > That said, do we still feel like there is a need for XMP in PNG?
> > (I'm not doubting it. I just want to make sure we check ourselves here.)
>
> It is already being used, at least in Adobe applications, so the need is
> already demonstrated and it is just a matter of registering this usage.
>
> It is also being done incorrectly by other applications, indicating a
> benefit to standardization:
>
>
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fnewsgroup.xnview.com%2Fviewtopic.php%3Ft%3D31356&amp;data=04%7C01%7Clrosenth%40adobe.com%7C6daf123658d94eb8a84c08d9b44ede1a%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637739073105324301%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=BGMp5SCdgADXnIEH7H7r%2BOK9R%2Bxl3MoA1DyFggb35MU%3D&amp;reserved=0
>
>  > XnViewMP writes XMP metadata in PNG files in the incorrect chunk, in
> the tEXt instead of iTXt, causing bad interaction with other
> applications which might lead to file corruption or loss of metadata.
>
> (Incorrect because tEXt is Latin-1 only, and because the convention is
> to use iTXt)
>
> > Exif has plenty of existing users and is a noticeable gap in PNG
> > compared to other image formats. It would be easy to justify why we
> > feel it should be included.
> > Does XMP cross the threshold of enough demand & users & clearly should
> > be part of the standard?
>
> It wouldn't be a new chunk; just a new registered keyword plus some
> pointers to the existing spec on what to put in the iTXt chunk.
>
> --
> Chris Lilley
> @svgeesus
> Technical Director @ W3C
> W3C Strategy Team, Core Web Design
> W3C Architecture & Technology Team, Core Web & Media
>