Lens Distortion Self-Calibration Using the Hough Transform

The Hough transform is a well known technique for detecting straight lines within images, especially in the presence of noise, or where there is incomplete data (gaps or occlusions). When subjected to lens distortion, straight lines become curved, and indeed this can be used to identify and correct lens distortion. However, curved lines distort and blur the peaks within the Hough transform, making the lines more difficult to detect. However, by analysing the distortion within the Hough transform, it is possible to directly estimate the lens distortion parameters enabling the distortion to be corrected in real time. The proposed technique uses a Terasic DE1-SoC FPGA board (Cyclone V FPGA) to fit a parabola to the distorted peak using Hough's original transform, and from the parabola coefficients directly estimates the lens distortion parameter. This enables the following frame to be corrected in parallel with curve detection.