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fftools/ffmpeg_filter: Fix autorotation

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In case of an orthogonal transformation av_display_rotation_get()
returns the (anticlockwise) degree that the unit vector in x-direction
gets rotated by; get_rotation in cmdutils.c makes a clockwise degree
out of this. So if one inserts a transpose filter corresponding to
this degree, then the x-vector gets mapped correctly and there are
two possibilities for image of the y-vector, namely the two unit
vectors orthogonal to the image of the x-vector.

E.g. if the x-vector gets rotated by 90° clockwise, then the two
possibilities for the y-vector are the unit vector in x direction
or its opposite. The latter case is a simple 90° rotation for both
vectors* whereas the former is a simple 90° clockwise rotation followed
by a horizontal flip. These two cases can be distinguished by looking
at the x-coordinate of the image of the y-vector, i.e. by looking
at displaymatrix[3]. Similarly for the case of a 270° clockwise
rotation.

These two cases were previously wrong (they were made to match
wrongly parsed exif rotation tag values).

*: For display matrices, the y-axis points downward.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2021-12-18 21:40:26 +01:00
parent b8a4b273be
commit 4e21fff19d
1 changed files with 2 additions and 2 deletions
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4
fftools/ffmpeg_filter.c
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@ -761,12 +761,12 @@ static int configure_input_video_filter(FilterGraph *fg, InputFilter *ifilter,
theta = get_rotation(displaymatrix);
if (fabs(theta - 90) < 1.0) {
ret = insert_filter(&last_filter, &pad_idx, "transpose", "clock");
if (displaymatrix[3] > 0) {
ret = insert_filter(&last_filter, &pad_idx, "hflip", NULL);
if (ret < 0)
return ret;
}
ret = insert_filter(&last_filter, &pad_idx, "transpose", "clock");
} else if (fabs(theta - 180) < 1.0) {
if (displaymatrix[0] < 0) {
ret = insert_filter(&last_filter, &pad_idx, "hflip", NULL);
@ -777,12 +777,12 @@ static int configure_input_video_filter(FilterGraph *fg, InputFilter *ifilter,
ret = insert_filter(&last_filter, &pad_idx, "vflip", NULL);
}
} else if (fabs(theta - 270) < 1.0) {
ret = insert_filter(&last_filter, &pad_idx, "transpose", "cclock");
if (displaymatrix[3] < 0) {
ret = insert_filter(&last_filter, &pad_idx, "hflip", NULL);
if (ret < 0)
return ret;
}
ret = insert_filter(&last_filter, &pad_idx, "transpose", "cclock");
} else if (fabs(theta) > 1.0) {
char rotate_buf[64];
snprintf(rotate_buf, sizeof(rotate_buf), "%f*PI/180", theta);