[vlc-devel] [PATCH 3/12] esformat: fix ORIENT_LEFT_BOTTOM and ORIENT_RIGHT_TOP descriptions

[Rémi Denis-Courmont]

Le sunnuntaina 27. syyskuuta 2020, 13.52.15 EEST Romain Vimont a écrit :
> Each one should be clearly documented and defined without ambiguities.
> 
> Without that, we cannot say whether "rotated 90 clockwise" is wrong or
> right: what is rotated compared to what? Just reverse the interpretation
> of an odd number of steps to get the opposite result.

The two non-involutive square transform are intrinsically ambiguous.

That's exactly why the orientations are named after the unusual but 
unambiguous EXIF convention instead. Orientation X-Y means that:
- the top of picture is encoded in X, and
- the left of the picture is encoded in Y,
with top-left being nominal.

And in any case, I only know two standard conventions, EXIF and MP4. MP4 is 
far more complicated, with a 2x2x16-bits matrix that support non-square 
transforms and overlaps with sample aspect ratio, so it's not really suitable.

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雷米‧德尼-库尔蒙
http://www.remlab.net/