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毕业论文基于MATLAB的车牌识别系统中图像预处理研究学院：电气工程学院专业：电子信息工程姓名：张黎宾学号:P081613538指导老师：刘文博2012年5月I基于MATLAB的车牌识别系统中图像预处理研究专业：电子信息工程姓名：张黎宾指导教师：刘文博摘要数字图像处理技术是自1960年以来发展起来的一门新兴学科，随着图像处理技术理论和方法的进一步完善，使得数字图像处理技术在许多领域得到了广泛的应用，并展现出广阔的应用前景。本文主要是研究车牌识别系统中一个重要的模块——图像预处理。为了使彩色图像减少存储信息，我们可以先对彩色图像进行灰度化，只保留该图像的亮度信息。本文通过传统的方法中值滤波和均值滤波对图像进行去噪，对结果比较分析，虽然中值滤波比均值滤波效果要好，但是图像还是含有较多的噪声。所以本文在小波变换的基础上进行了改进，图像经过小波变换后再进行中值、均值滤波去噪，这样也再次把中值、均值滤波进行对比。通过对效果图的分析和总结，改进后的去噪效果要比之前的更好，同时改进后的中值滤波还是比均值滤波好一些，因此基于小波变换的中值滤波是值得采用的。本文提出的针对车牌图像的预处理过程对灰度图像可以达到不错的效果，并且在一定的程度上解决了因外界因素而造成的车牌图像对比度较低的问题。关键词数字图像处理，预处理，中值滤波IIABSTRACTDigitalimageprocessingtechnologyisIemergingsubjectsince1960,theameliorationofimageprocessingtheoryandmethodsgetstheDigitalimageprocessingtechnologytobeappliedwidelyinmanyfieldsandpresentabroadapplicationprospectinthedaystocome.Thispaperismainlyresearchvehicleplaterecognitionsystemaimportantmodule——imagepreprocessing.Inordertomakethecolorimagetoreducethestorageinformation,wecanfirstonthegrayofthecolorimages,justretainingthebrightnessinformationoftheimage.Thisarticlethroughthetraditionalmethodofmedianfilterandmeanfilterforimagenoisereductiontocomparativeanalysistheresult,althoughtheeffectofmedianfilteringisbetterthanthemeanfilter,theimagesstillcontainlotsofnoise.Therefore,thispapermakesimprovementonthebasisofwavelettransform,imageafterwavelettransform,noisereductionofthemedianfilteringandmeanfilter.Itcomparedthemedianfilteringandmeanfilteroncemore.Accordingtotheeffectgraphanalysisandsummary,theeffectoftheimprovednoisereductionisbetterthanbefore,atthesametime,theimprovedmedianfilteringisalsobetterthantheimprovedmeanfilter,sobasedonwavelettransformisworththemedianfilter.Theideaofvehicleplaterecognitionsystemwillearnapositiveresultasfarastheprayimageisconcernedand,tosomedegree,resolvetheproblemevokedbyinternaldampers.IIIKeyWords：Digitalimageprocessing,Pre-processing,Medianfiltering目录1绪论...................................................................11.1课题的研究背景.....................................................................................................................................11.2车牌识别系统的原理.............................................................................................................................11.3国内车牌特征.........................................................................................................................................21.4本文的结构安排与主要工作.................................................................................................................32MATLAB简介.............................................................52.1初识MATLAB........................................................................................................................................52.2MATLAB的基本功能............................................................................................................................63图像灰度化与增强.......................................................73.1灰度化.....................................................................................................................................................73.2二值化.....................................................................................................................................................83.3图像增强...............................................................................................................................................103.3.1图像增强的背景与定义........................................................103.3.2图像增强的意义..............................................................113.4直方图...................................................................................................................................................113.5直方图均衡化.......................................................................................................................................133.5.1直方图均衡化的背景..........................................................133.5.2直方图修正技术的基础........................................................143.5.3直方图的均衡化..............................................................154滤波去噪..............................................................184.1中值滤波...............................................................................................................................................184.1.1中值滤波的定义..............................................................184.1.2中值滤波的基本原理..........................................................184.2均值滤波...............................................................................................................................................194.2.1均值滤波的定义..............................................................204.2.2均值滤波的基本原理..........................................................204.3基于小波变换的均值、中值滤波图像去噪.......................................................................................234.3.1小波变换....................................................................234.3.2对小波变换进行改进..........................................................244.4小结