HDR support

[da2x]

Hi, any chance you could add support for 10 and 12-bit color depth, please? Either switching automatically based on the source image or using a command argument.

I’ve experimented with it in link-u/cavif, and the files are only 1–2 % bigger and still way smaller than the 8-bit JPEG/WebP equivalent.

[kornelski]

Yeah, that's doable.

[gitoss]

Yeah, that's doable.

+1 for this request, 10bit shows better performance even for 8bit sources

Libavif does 10bit, but releases or binaries around don't include rav1e (yet) :-\

[Ralith]

HDR metadata support would go nicely with this!

[kornelski]

I don't understand how HDR metadata support would help generating correct HDR files.

This crate supports JPEG and PNG as input, and AFAIK neither of these are good for HDR. I can put HDR metadata, but how do you get HDR pixels in?

[Ralith]

My interest is for using the ravif library to encode HDR data I generate myself; I don't know if it's relevant to transcoding from LDR using the command line tool, though it might be convenient for testing. Perhaps there's some esoteric form of JPEG that encodes the same metadata that would be nice to preserve?

[Ralith]

Is that something you consider in-scope, @kornelski?

[kornelski]

Use-case for programmatically-generated data makes sense. ravif could definitely support it, even if the CLI tool can't.

I haven't had time to play enough with HDR images to know how to best handle them. In my experience—for SDR—the separation between pixel data and color profiles that alter the meaning of the data is inelegant and has lead to a lot of broken software. Is is possible to make a better API for HDR data?

[Ralith]

HDR metadata is standardized and absolutely necessary, because it informs the ultimate display device of how to most effectively tonemap, avoiding unnecessary quality loss in common cases. I'm all in favor of designing an API to make it as difficult as possible to have missing/incorrect metadata, but it's not obvious to me what that would look like. Maybe require HDR metadata always be supplied if a HDR color space is used, for starters?

[kornelski]

10-bit encoding of sRGB has been released.

Encoding of HDR is still an open issue. What formats would you supply HDR images in? OpenEXR?

[Ralith]

That's again a non-issue for library users, which can just pass in raw uncompressed HDR10 bitmaps. Raw half-float bitmaps might also be useful.