High-precision calibration of wide-angle fisheye lens with radial distortion projection ellipse constraint (RDPEC)

This paper presents a novel technique for wide-angle fisheye lens calibration which requires neither metric information nor particular reference pattern. First, the fisheye imaging model with the interior Orientation parameters (IOPs)—principal point (u0,v0), focal length f, aspect ratio λ and radial distortion coefficients (k1, k2), is established. Then, upon the fisheye imaging model and the parameter dependency between f and (k1, k2), the radial distortion projection ellipse constraint (RDPEC) for space lines in fisheye image is mathematically formulated to build a non-linear calibration model for high-precision estimation of the IOPs. In this step, parameter initialization based on the geometry of fisheye image outline ellipse (FIOE) is discussed as well. Finally, initial IOPs are further optimized though least square technique by taking the projection ellipse arcs of space lines in fisheye image as observation. The proposed calibration technique was tested on two kinds of fisheye images: (a) simulated image with a set of ground-truth IOPs, (b) internet images with unknown IOPs. Experimental results show that the calibration parameters in this paper are in the best agreement with the fisheye imaging model, compared with the ground-truth parameters and the parameters estimated by two state-of-the-art literature. Compared to that by a state-of-the-art CNN and the well-known software DXO, the proposed technique can enable a high-quality correction of fisheye images in different regions. This makes it very useful in application scenarios containing space lines, such as urban panorama surveillance, auto-parking and, robot navigation.