Uhdr write

[mugulmd]

Assisted-by: claude-code / opus-5

Description

Related to #5229.

In its current state, OpenImageIO only supports reading Ultra HDR images, and does not support writing such images.

This feature has been requested because it enables converting an HDR image from specialized formats such as OpenEXR to widely-supported and easily displayable/exchangeable JPEG files.

libultrahdr (the codec we use for Ultra HDR) has plenty of options but we only use a restricted subset for simplicity, which leads to the following constraints:

• incoming image data must be half or float
• oiio:ColorSpace must be one of lin_rec709_scene, lin_p3d65_scene, lin_rec2020_scene because it needs a corresponding "Ultra HDR color gamut".

Also, in order to trigger the Ultra HDR output path, the incoming image must have the jpeg:ultrahdr metadata set to any non-zero integer.

Tests

3 tests have been added to jpeg-ultrahdr:

• synthesize an Ultra HDR image, write it, then ensure reading it back succeeds
• ensure writing an Ultra HDR image with integer data fails
• ensure writing an Ultra HDR image with an unsupported color space fails.

Checklist:

• I have read the guidelines on contributions and code review procedures.
• I have read the Policy on AI Coding Assistants
  and if I used AI coding assistants, I have an Assisted-by: TOOL / MODEL
  line in the pull request description above.
• I have updated the documentation if my PR adds features or changes
  behavior.
• I am sure that this PR's changes are tested in the testsuite.
• I have run and passed the testsuite in CI before submitting the
  PR, by pushing the changes to my fork and seeing that the automated CI
  passed there. (Exceptions: If most tests pass and you can't figure out why
  the remaining ones fail, it's ok to submit the PR and ask for help. Or if
  any failures seem entirely unrelated to your change; sometimes things break
  on the GitHub runners.)
• My code follows the prevailing code style of this project and I
  fixed any problems reported by the clang-format CI test.
• If I added or modified a public C++ API call, I have also amended the
  corresponding Python bindings. If altering ImageBufAlgo functions, I also
  exposed the new functionality as oiiotool options.

[lgritz]

Hi, @mugulmd, just a reminder that this is still marked as a draft, needs a DCO, and has some clang-format fixes. I think that the "hobbled" failure is unrelated and has been separately fixed, should be fixed if you rebase this on top of the current main.

[mugulmd]

Hi @lgritz yep sorry I just reached the stage of "this works on my machine, let's make a draft PR and finish this later" and I've been procrastinating a little bit 😅 I have some spare time in the days to come, I'll finish this properly!

[lgritz]

Can you rebase on top of current main to fix the apparent conflict in buildinplugins.rst?

I wonder if the conflict is related to the several places where you seem to have changed whitespace, probably something your editor or pre-commit hooks did automatically?