基于频率域点扩散函数的视频中运动模糊车牌复原与识别优化

Optimization of License Plate Image Restoration and Recognition in Video with Motion Blur Based on Frequency Domain Point Spread Function

车辆是刑事案件中常使用的工具,车牌识别是涉案车辆认定的重要依据之一,因此对运动模糊造成的车牌图像退化的复原是刑事技术工作的重要研究方向。文中提出一种基于频率域点扩散函数参数估计的车牌图像复原算法,运用二维离散傅里叶变换、Radon变换以及Wiener滤波算法解决监控视频视角下运动模糊车牌的复原问题。通过预处理对运动模糊图像进行灰度化和降噪,并对图像添加Hanning窗,进行二维离散傅里叶变换和对数运算,计算图像的功率频谱图,运用Radon变换对频谱图进行检测,估算模糊方向;对频谱图进行最小值计算,求模糊长度,完成对点扩散函数两个参数的估算。通过Wiener滤波算法进行图像反卷积,实现图像复原。针对传统频谱图估算模糊参数易受中央亮线干扰的问题,在离散傅里叶变换之前添加窗函数进行优化。使用道路监控拍摄的模糊图像,进行点扩散函数参数估计实验,同时与目前未加窗的方法进行对比,验证所提算法的复原效果。实验结果证明,所提算法在复原车牌图像语义信息方面具有优势,能为刑事图像技术领域模糊车牌复原提供方法补充。

Vehicles are commonly used tools in criminal cases,and license plate recognition is one of the crucial criteria for identi-fying involved vehicles.The restoration of license plate images degraded by motion blur is an important research direction in digi-tal image processing.This paper proposes a license plate image restoration algorithm based on the estimation of frequency domain point spread function parameters.It utilizes two-dimensional discrete Fourier transformation,Radon transformation,and the Wiener filtering algorithm to address the problem of restoring license plates affected by motion blur in surveillance video angles.The process starts with preprocessing the motion-blurred image by converting it to grayscale and reducing noise.A Hanning window is applied to the image,followed by two-dimensional discrete Fourier transformation and logarithmic operations.This computes the power spectrum of the image.Radon transformation is used to detect the spectrum and estimate the blur direction.The minimum value computation on the spectrum determines the blur length,which completes the estimation of the two parameters of the point spread function.The image is then deconvolved using the Wiener filtering algorithm,resulting in the restoration of the image.To address the issue of traditional spectrum estimation being susceptible to interference from central bright lines,a window function is added before the discrete Fourier transformation.To validate the algorithm’s restoration effect,experiments are conducted with motion-blurred images captured by road surveillance.These experiments are compared with the non-windowed me-thod,establishing a method for restoring motion-blurred license plate images.Experimental results demonstrate that the proposed algorithm has an advantage in preserving the semantic information of license plate images and can complement the field of criminal image technology in the restoration of blurred license plates.