Removing Color Stain on Vehicle License Plates Based on Photometric Stereo and a Hole-Filling Algorithm

Although recognition of vehicle license plate is well studied, characters can be obscured by color stains due to rust, mud, peeling paint or fading colors and become unrecognizable. In this paper, two approaches are presented to remove stains from license plate images by using photometric stereo technique and hole filling algorithm of texture synthesis respectively. The former method extracts height information and abandons color information of the license plate and the later one restores the characters on the plate in a texture synthesis scheme. These two methods are proved to be effective to clean the blurry license plate images, which provide a better input for the successive processes, such as character segmentation and recognition.