Fisheye is a type of super-wide-angle lenses with uncorrected distortion, resulting in strong geometric distortions of the resulting image. Fisheye dewarping is used to eliminate these distortions.
Fisheye lenses are usually divided into two main varieties according to the degree of frame filling: circular and full-frame. In circular lenses, the circle of the image received from the camera is inscribed in the frame. In full-frame lenses, on the contrary, the frame is inscribed in the circle of the image from the camera.