On Wed, Jan 12, 2022 at 5:00 PM Michael Koch <[email protected]> wrote:
> Hello, > > I have a projector with a 180° fisheye lens in a dome. Things are easy > if the lens is at the center of the dome. Any input format can be > transformed to fisheye output with the v360 filter. But things are > getting complicated when the lens isn't at the dome's center. Let's > assume the dome has 1m radius and the lens is shifted 0.5m to the side. > In this case the +60° point from the input image must be mapped to the > center of the output image (because acos(0.5) = 60°) ). > The center of the input image must be mapped to 63.4° in the output > image (because 90° - atan(0.5) = 63.4°). > > The v360 filter has h_offset and v_offset options. There isn't much > documentation for these options, so let's just try out what they do. > I'm using the test pattern from Paul Bourke: > http://www.paulbourke.net/dome/testpattern/1200.png > > ffmpeg -i 1200.png -vf v360=fisheye:fisheye:h_offset=0.5 -y out.png > > The +60° point from the input image is not mapped to the center of the > output image, that's wrong. > The center of the input image is mapped to +60°, that's also wrong. > > > Next I did try 0.577 (=tan(30°)) as offset: > > ffmpeg -i 1200.png -vf v360=fisheye:fisheye:h_offset=0.577 -y out.png > > Now the +60° point from the input image is mapped to the center of the > output image, that's good. > The center of the input image is mapped to about 54.5°, that's wrong. > > > These results leave me with two questions: > -- Obviously the offset options aren't doing what I was hoping for. What > else are they supposed to do? > -- How can a fisheye image be transformed to an off-center fisheye image? > http://paulbourke.net/panorama/sphere2persp/ I got idea from that one, and I believe its correctly implemented. > > Michael > > _______________________________________________ > ffmpeg-user mailing list > [email protected] > https://ffmpeg.org/mailman/listinfo/ffmpeg-user > > To unsubscribe, visit link above, or email > [email protected] with subject "unsubscribe". > _______________________________________________ ffmpeg-user mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
