PNG Specification (Third Edition) W3C Working Draft 20 July 2023 | Hacker News Reader

PNG Specification (Third Edition) W3C Working Draft 20 July 2023

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58 pointsrobin_reala22 comments

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Changes since the 2nd edition of PNG:[1]

- APNG added to the spec

- A new CICP chunk that paves the way for HDR support

- EXIF part of the main spec

- Various other fixes

[1] https://www.w3.org/TR/png-3/#changes-20031110

> EXIF

.. because we all need UUIDs and device origin on every image on the net?

The chunk is ancillary, so if size matters it can be omitted.

Size is not the problem. Privacy is.

Pretty sure there was metadata in there already. Stablediffusion has been saving data into there for awhile now. It's not evil in intent. Just strip it out.

XMP metadata: https://dev.exiv2.org/projects/exiv2/wiki/The_Metadata_in_PN...

If you're relying on file formats to preserve your privacy you've already lost.

So make sure your image processing pipeline strips out all metadata?

Seems kind of a non-issue and AFAIK most image hosting software and social media already strips out metadata anyway for this reason (I know Discord does, not sure about others)

then don't add that chunk to your files...

or write a tool which strips it... it's an easy format.

feel free to complain, but also take action, or it's all wasted breath and whining. no one wants to hear people describe their problems poorly while also taking zero action to fix those problems.

EXIF is valuable metadata for many use cases. Location data and fingerprinting are absolutely problems and the solution is to strip that information before you post images anywhere. Having it in the spec is a net win for privacy because it provides a standard chunk for it so that tools can universally strip it out.

Worked on a small charity project a few years ago, that included coordinating images with their geolocation for a specific trail to mark signage, etc. Was definitely useful. Not useful was the image orientation displaying differently in different browsers.

> Not useful was the image orientation displaying differently in different browsers.

There are bugs in SW emgineering which whitstand the test of time. This is one of them.

From Android to Windows to linux every program will have its own idea about orientation. I just gave up and just rotate the picture when possible and needed.

Yeah, I had thought about adding a control to strip the orientation data and reorient the picture as indicated, but had run out of time. Was definitely a learning experience.

EXIF is an arbitrary metadata schema. Nothing about it implies or mandates UUIDs and device origin.

UUIDs, I've never seen in EXIF.

Device origin, if I interpret as "camera model" or "GPS if enabled", I have seen.

I guess my question is, PNG already has an arbitrary metadata chunk, what does EXIF bring to the table that is not already there?

No but adding attribution and licensing to an image would be very useful.

Reliable date information too.

> No but adding attribution and licensing to an image would be very useful.

EXIF... If I remember correctly, EXIF uses the TIFF file structure. Am I right? Does this mean that a PNG file, with its relatively simple format, would have inside it an EXIF chunk with a potentially different byte order and absolute offsets all over the place?

Thank you for this...W3C specs tend to be the more confusingly structured ones, in my experience. I had a hell of time finding this.

Is this by the same people or is it a competitor to the PNG development group (http://libpng.org/pub/png/)?

The latter's website still heavily says that PNG is a still image only format, and promotes MNG as the animation alternative. Of course, that's not how web browsers have played it out, and it also appears to me that the libpng source code still lacks "APNG" support. This makes me think it's a competing standard to the original developers.

The authors and editors overlap with the original specification's authors. It would appear that, if the PNG group is still publishing a standard, that this is at least the spiritual successor.

Also, this is still a working draft, so it's unlikely libpng (a notoriously conservative, for good reasons, library) would implement the standard until it has been accepted and ratified. So that's not really an indicator of their support for it or not.

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