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georgmartius / vid.stab

Video stabilization library
http://public.hronopik.de/vid.stab/
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Restrict alpha to values from -pi to pi in new_transform #92

Closed gkraberger closed 4 years ago

gkraberger commented 4 years ago

Hi,

I sometimes observed a frame-flipping issue when using vid.stab with ffmpeg, i.e. the video would turn upside-down and then back to normal again. After some investigation, I found out that the reason was that the rotation angle that was found in the gradient descent procedure (within vsMotionsToTransform) was around 2 pi for a frame. Then, during the averaging process in cameraPathGaussian, a transformation of a frame with an angle of ca. 0 rad was averaged with an angle of ca. 2 pi, resulting in an angle of ca. pi, i.e., a flip. (In reality, of course, the averaging is more complicated as there are more terms with different weights).

I found that restricting the angle to values from -pi to pi in new_transform fixes that problem.

Regards, Gernot

georgmartius commented 4 years ago

Hi Gernot,

thanks a lot for spotting and fixing this bug.

Georg