[digikam] [Bug 509976] PNG and HEIF not rotated correctly

[bugzilla_noreply at kde.org]

https://bugs.kde.org/show_bug.cgi?id=509976

--- Comment #15 from ferse_palette.0y at icloud.com ---
Thank you, Maik, for your time. I appreciate it. Since you took your precious
time, I decided to take some of mine to respond, and test some more things. 

(In reply to Maik Qualmann from comment #13)
> 1) When converting from TIFF to PNG, the image is of course not
> automatically rotated; the PNG is aligned identically to the TIFF. The step
> of automatically rotating according to Exif information is necessary.
That makes sense once you know it, but I can’t help it finding it somehow
unintuitive. If I were to program digikam just for me, I’d add a setting in the
export options of batch queue manager (BQM) to auto-rotate before saving. I
know there could be several opinions on this, just sharing my data point.

> The lossy rotation option must be enabled for this.
This is the most unintuitive thing for me. I would strongly suggest rewording
the UI options then. I read this:
Rotate by changing the content if possible → rotate all the lossless formats
when it’s possible (or the lossy ones where lossless rotation is possible)
Even allow lossy rotation if necessary → even rotate the lossy formats
But what you actually say is that I need to check the lossy box for it to
rotate lossless formats like TIFF and PNG. This doesn’t make sense to me at
all. Again, maybe it’s just me, but for this one, I’m more confident that many
other users might feel this way.

> 2) The same as with PNG, but the HEIF image must be re-encoded, so loss may
> occur.
Now that I understood the logic, it worked both with PNG and HEIF — by manually
auto rotating (using "Auto Rotate/Flip Using Exif Information") the TIF before
exporting. See below.

> It's best to temporarily disable the display of images rotated according to
> Exif information in digiKam. Then you'll see images as your users see them
> with programs that don't support this.
Interesting. It’s not quite how MacOS programs show the images, but it’s still
useful. 

> I just saw that this tool already exists under Transform/Rotate (not the Auto-Rotate tool). By default, it can rotate based on Exif information.
> Always add this tool first, then the tool for converting to the appropriate image format. This way, there's no double encoding, for example, with > HEIF images.
The tool looks indeed like the right one, but unfortunately it produces very
surprising results. Neither the PNG or the HEIF that resulted from it were
rotated correctly in digikam. Not even the TIF alone was rotated correctly.
However, for whatever reason, the HEIF was rotated correctly in MacOS. Anyway,
that was all too little reproducible for me.

Since I wanted to contribute for future users, I ran some more tests with the
options you suggested. Long story short: the only thing that worked fine was:
allowing lossy rotation (see above on my opinion on this :) ), manually auto
rotating (using "Auto Rotate/Flip Using Exif Information"), then exporting
(using BQM) to HEIF or PNG (both worked fine). If lossy rotation was not
allowed, things didn’t go well.

To allow you to reproduce the steps, I uploaded the images with names that
explain the previous steps:

https://lufi.ethibox.fr/r/Eep4QQ6T41#5SmthAbR0zjTdt3qBdZ3fbZSg6PnC5nRyUYdBZdu6po=

If you think there is a value in one of the three things that I mentioned (1)
incorporate rotation before export as an option; 2) rename lossy option or
change the way it works; 3) change the working Auto-Rotation option in BQM to
work like the option in the Item menu), I’d be happy to rephrase them or create
separate items for them. In the meantime, I don’t touch anything.

Have a great day, and all the best!

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