An Image Enhancement Method of Nighttime Blurred Vehicle Plate Based on BHPF

Character segmentation and recognition of nighttime blurred license plate is a difficult problem for vehicle recognition.An image enhancement method based on Butterworth high pass filter(BHPF) which can select stop-frequency adaptively depending on energy is presented to solve the problem.The license plate can be got after the object location.Because of the influence of vehicle lamp and lower visibility,the object is usually blurred.The vehicle license sharp part with characters is extracted by BHPF depending on images frequency feature.Then the stop-frequency selection is selected adaptively by energy collected in low frequency part.The enhancing high pass filter is designed to enhance images and the object binary image is fit for character segmentation.Seriously degraded nighttime blurred license plate images taken from real world are used in the experiments to evaluate the robustness,flexibility and effectiveness of the approach.The character segmentation and binary result keep useful information more accurately to be used as character recognition.