[Dylan16807]

If someone edits a png I expect them to output a new file. So if they use the SDR version as a starting point... they use the SDR version, that's it, nothing else breaks. Everyone sees the same output from Sarah. You can have the same kind of issues with baseline png already; not every tool does all colors or editing effects correctly, and if someone uses a worse tool to edit then that's unfortunate.

[solardev]

Right, but not everyone is going to start from the SDR. Some might have the HDR version and not realize they're destroying the info. It gets worse the more forks and features you have.

There's just no advantage in overloading an old graphics format for something like this in a world where WebP and AVIF already exist.

As for editing tools, at least they're targeting the same baseline format (maybe with bugs). This is purposefully introducing new features that can only be used in some places, outside of the agreed standard.

[cycomanic]

Sure there is an advantage, I can put a png file everywhere without needing to care if the users system supports the new capability.

For a (made up) example let's say Firefox supports hdr, but Chrome doesn't, if I want to include an HDR image into a website, but display a SDR image if the browser can't display it, I need to implement a test for the browser to serve decide if I serve a WebP or PNG. That is a real cost.

[solardev]

What you see as a positive I see as potential for implementation details to diverge and cause user issues. We already have issues with WebP and AVIF rendering in some versions of Safari, and those are well established standards, not a lone wolf extension.

In theory an extended hacked PNG would have perfect backward compatibility, but the complexities of codecs more likely means it's going to appear as bugs in several implementations. Best case it falls back to SDR, but it's also possible some broken implementation leads to HDR content being displayed in a SDR setup and everything getting all washed out.

Having the same file format/extension actually host several different versions never works well. Graphic artists and support teams have to deal with rendering quirks like this all the time because some developer thought their hack was a genius overload :/

[Sardtok]

This is built into HTML, where you can supply multiple files in a srcset.

[sroussey]

Does srcset have a mechanism for SDR vs HDR?

[solardev]

Yeah, if they just specify a WebP or AVIF version.

[sroussey]

HDR AVIF is not supported in safari, so how do you work around that?

And webp doesn’t support HDR at all.