[wp-trac] [WordPress Trac] #62285: HDR AVIF is corrupt in the media library (encoded as SDR)

[WordPress Trac]

#62285: HDR AVIF is corrupt in the media library (encoded as SDR)
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 Reporter:  gregbenz      |       Owner:  adamsilverstein
     Type:  defect (bug)  |      Status:  assigned
 Priority:  normal        |   Milestone:  6.8
Component:  Media         |     Version:
 Severity:  normal        |  Resolution:
 Keywords:                |     Focuses:
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Comment (by gregbenz):

 @adamsilverstein I believe the simplest approach would be to stay at the
 same bit depth, up to a maximum of 12. This would ensure retention of
 suitable quality without penalty if the original is encoded in an
 appropriate bit depth.

 If your assumption is that many people will create originals with higher
 bit depth than necessary and you wish to prioritize small file size, you
 could take a more complex approach - at the risk of some edge cases where
 unwanted banding is created. For example, you could use 8-bits for SDR
 EOTFs and 10-bit for HDR EOTFs. That’s fairly crude, but probably safe for
 99% of images. If a way for a user to select higher quality could be
 offered, that could be a good choice.

 Ultimately, the benefit for higher bit depths (SDr at 10, HDR at 12) would
 mostly likely show when there is a smooth gradient across a sufficient
 tonal range. 10-bit encoding does generally work well for HDR capabilities
 we have today, 12-bit is probably more of a consideration for future
 proofing.

 I’m not aware of an efficient way to assess that in code, and I would
 recommend keeping source depth or perhaps using the 10-bit HDR with a user
 option to go higher if needed.

 As far as file size impact, I don’t have data on it. I expect that 12-bit
 encoding will rarely be used where not necessary, so probably minimal
 impact in real use. Compression may impact the results, but you might
 estimate 20% bloat if 12-bit were needlessly used in the source (ie missed
 opportunity to improve). I would err on the side of assuming that if the
 image was exported at 12-bit that it is more likely beneficial and
 squeezing to 10 risks banding.

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Ticket URL: <https://core.trac.wordpress.org/ticket/62285#comment:8>
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