Originally Posted by troyz
As jjj notes, rectilinear de-fishing of images with a wider field of view (shorter focal length) becomes problematic due to excessive stretching of the corners of the image. Fisheye-Hemi (and other cylindrical projections) get around this problem by straightening vertical elements of the image but not the horizontal elements.
So fisheye-hemi just projects the image cylindrically and I could use any many free/open source programs that do cylindrical projections to defish images with similar effect? That would be interesting.