Estimate and Eliminate Background of Image with Top-hat Transformation

Top-hat transformation can be used in image preprocessing for location of license plate, in order to estimate and eliminate the background of license plate image. A structure element is established which diameter is more than 16. Then the structure element is split to a few simple structure elements, for the increasing of speed in grey morphologic operation. For license plate image, the several structure elements are adopted in proper order, grey dilation after grey erosion namely grey open operation are taken, so the approximate background image is got. Then the original image is subtracted by the background image, consequently, background is eliminated, license plate area is reserved, and location disposing is favorable.