Metadata gone on png rotation (XMP, ICC profile, EXIF)

[eugenesvk]

Original PNG (screenshot with a few bits of EXIF, XMP, ICC metadata)

PNG rotated in Oculante

Note that all XMP, ICC profile, EXIF metadata is gone

This might be due to the fact that the PNG lib oculante uses forgot to update to the "newer" PNG spec that supports metadata?
(from this SO answer EXIF is part of the PNG spec since 2017 (Version 1.5.0 (July 2017) of the Extensions to the PNG 1.2 Specification)

[woelper]

All images end up as a generic image buffer when loaded, without any extra data - so this is expected. I would have to find a way to preserve this in a generic way to re-apply when saving.
On top of that, image does not easily support this (image-rs/image#1045) so I doubt this would be easy.

[eugenesvk]

Oh, ok. For the exif data I'd repeat my comment from the sidecar issue: wait for the library to handle it (there are some solutions in that thread, not sure how viable they are)

The correct handling of color profile passthrough is tied to the ability to handle color profiles in general (since you might edit in a different one)?

So maybe just add a limitation note in the readme that this metadata is lost?

[woelper]

I have been thinking about this, and since oculante supports loading of metadata and stores it in memory, it could write that upon saving, even if the underlying library does not do that by default. I'll try to prototype something for a small set (maybe png/jpeg first) and see how that works. I'd probably check for metadata being present and write it after saving to the file.

[woelper]

I've made a branch for this (linked) which seems promising. It's a bit brutal since it's a post-process, but it completely preserves EXIF, even if you save from jpeg to png or tiff.

[woelper]

Metadata should now be preserved as-is when saving.