FPGA-based distortion correction for laser spot inspection system

This paper focuses on the correction of radial distortion in the laser spot vision inspection system, which is the main cause for the inaccuracy of measurement results. An efficient circuit architecture using a low cost FPGA (field programmable gate array) and a hardware look-up table for distortion correction is presented. The polynomial fitting formula between the pixels in the distorted image and those in the corrected one will be calculated under software circumstance, then converted into the addresses of FLASH memory as a look-up table. By access to FLASH memory instead of complex arithmetic, FPGA can obtain the spatial correction data, according to which the gray scale can be gained and corrected with a nearest-neighbor principle. Experiment results illuminate the relative distortion declines from 23.88% to approximately 1%, and the average error of the spot center is within 1mm. The reduction of distortion error facilitates the application of the short-focus and wide-angle lenses, and therefore promotes the development of portable and miniaturized instruments.