trshaner wrote:
DxO Viewpoint can also correct this, which they call “volume anamorphosis."
Actually that was once the subject of a very lengthy discussion in the PS forum. What came out of it was that there is really no way to correct that without introducing some kind of barrel or cylinder distortion - but the example images on the DxO website were carefully chosen to conceal that fact. It worked, but only on a certain type of images. On others it would just substitute one form of distortion with another.
Don't ask me to quote the exact laws of physics, I would have to look it up, but intuitively it clicks with me. There's a reason wide angle lenses have this corner stretching in order to preserve straight lines. If there wasn't, they wouldn't.