数字图像处理,冈萨雷斯,课件英文版Chapter08图像压缩.ppt

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1、DigitalImageProcessingChapter8:ImageCompression11August2006DatavsInformationInformation=Matter(สาระ)Data=ThemeansbywhichinformationisconveyedReducingtheamountofdatarequiredtorepresentadigitalimagewhilekeepinginformationasmuchaspossibleImageCompressionRelativeDataRedundancyandCompressio

2、nRatioRelativeDataRedundancyCompressionRatioTypesofdataredundancy1.Codingredundancy2.Interpixelredundancy3.PsychovisualredundancyCodingRedundancyDifferentcodingmethodsyielddifferentamountofdataneededtorepresentthesameinformation.ExampleofCodingRedundancy:VariableLengthCodingvs.FixedLen

3、gthCodingLavg3bits/symbolLavg2.7bits/symbol(ImagesfromRafaelC.GonzalezandRichardE.Wood,DigitalImageProcessing,2ndEdition.VariableLengthCodingConcept:assignthelongestcodewordtothesymbolwiththeleastprobabilityofoccurrence.(ImagesfromRafaelC.GonzalezandRichardE.Wood,DigitalImageProcessing

4、,2ndEdition.InterpixelRedundancyInterpixelredundancy:Partsofanimagearehighlycorrelated.Inotherwords,wecanpredictagivenpixelfromitsneighbor.(ImagesfromRafaelC.GonzalezandRichardE.Wood,DigitalImageProcessing,2ndEdition.RunLengthCodingThegrayscaleimageofsize343x1024pixelsBinaryimage=343x1

5、024x1=351232bitsLineNo.100RunlengthcodingLine100:(1,63)(0,87)(1,37)(0,5)(1,4)(0,556)(1,62)(0,210)Total12166runs,eachrunuse11bitsTotal=133826Bits(ImagesfromRafaelC.GonzalezandRichardE.Wood,DigitalImageProcessing,2ndEdition.PsychovisualRedundancyTheeyedoesnotresponsewithequalsensitivity

6、toallvisualinformation.8-bitgrayscaleimage4-bitgrayscaleimage4-bitIGSimageFalsecontours(ImagesfromRafaelC.GonzalezandRichardE.Wood,DigitalImageProcessing,2ndEdition.ImprovedGrayScaleQuantizationPixeli-1ii+1i+2i+3GraylevelN/A01101100100010111000011111110100Sum000000000110110010010111100

7、0111011110100IGSCodeN/A0110100110001111+Algorithm1.Addtheleastsignificant4bitsofthepreviousvalueofSumtothe8-bitcurrentpixel.Ifthemostsignificant4bitofthepixelis1111thenadd0000instead.KeeptheresultinSum2.Keeponlythemostsignificant4bitsofSumforIGScode.FidelityCriteria:howgoodisthecompr