Error in double-fisheye to equirectangular conversion

[Michael Koch]

There is a rounding or +-1 error in the double-fisheye to equirectangular conversion. Can be reproduced as follows:

ffmpeg -f lavfi -i color=red:s=20x20 -f lavfi -i color=green:s=20x20 -lavfi hstack,v360=dfisheye:e -frames 1 -y out.png

[Michael Koch]

Another problem is that the pixels in the output image appear twice as big as they should be. What looks like one pixel is in fact 2x2 pixels.

[Michael Koch]

Same problem also when converting from equirectangular to double-fisheye. The pixels are twice as big as they should be.

ffmpeg -f lavfi -i color=red:s=10x20 -f lavfi -i color=green:s=20x20 -lavfi [0]split[a][b];[a][1]hstack[a];[a][b]hstack,v360=e:dfisheye -frames 1 -y out.png

[Elon Musk]

used subsampled inputs.

[Michael Koch]

The first problem was fixed here

​http://ffmpeg.org/pipermail/ffmpeg-cvslog/2021-October/129405.html

and here

​http://ffmpeg.org/pipermail/ffmpeg-cvslog/2021-October/129406.html

Thank you!

The second problem was my fault, because the input was subsampled.