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

[Romain Vimont]

On Sat, Sep 26, 2020 at 08:17:42PM +0300, Rémi Denis-Courmont wrote:
> Le lauantaina 26. syyskuuta 2020, 19.48.21 EEST Romain Vimont a écrit :
> > What is the meaning of ORIENT_XXX_YYY?
> 
> Names are the same as in EXIF.

http://jpegclub.org/exif_orientation.html
https://web.archive.org/web/20080106081516/http://park2.wakwak.com/~tsuruzoh/Computer/Digicams/exif-e.html#IFD0Tags

> +-------+------------+------------+
> | Value | 0th Row    | 0th Column |
> +-------+------------+------------+
> | ...   |            |            |
> | 6     | right side | top        |
> | ...   |            |            |
> +-------+------------+------------+
>
> Entry #6 in the table says that the 0th row in the stored image is the
> right side of the captured scene, and the 0th column in the stored
> image is the top side of the captured scene.

So IIUC, following that logic, ORIENT_LEFT_BOTTOM means:

        captured    stored   displayed
         A---B      D---A      A---B
         |   | ---> |   | ---> |   |
         D---C      C---B      D---C

The first row in the stored image (D-A) is the left side of the captured
image, and the first column (D-C) in the stored image is the bottom side
of the captured image.

> [video_orientation_t] represents how the the orientation of the
> encoded image.

Therefore, ORIENT_LEFT_BOTTOM corresponds to "rotated 90 degrees
clockwise" (the stored image is the captured image rotated by 90 CW),
doesn't it?

Regards