《電子與通信工程專業(yè)英語(yǔ)》課件第8章

Unit8JPEG2000:RetrospectiveandNewDevelopmentsNEWWORDSANDPHRASES

NOTES EXERCISES

參考譯文

EXTENSIVETEXT

1．Introduction

JPEG2000isanewimagecompressionstandarddevelopedundertheauspicesofISO/IECJTC1/SC29/WG1(commonlyknowastheJointPhotographicExpertsGroup(JPEG)committee).Thestandardmakesuseofseveralrecentadvancesincompressiontechnologytodeliversuperiorcompressionperformanceandprovidesmanyadvancedfeaturesinscalability,flexibility,andsystemsfunctionalitiesthatoutperformitspredecessor,theoriginalJPEGstandard[1].Inparticular,JPEG2000usesadiscretewavelettransform(DWT)inplaceofthediscretecosinetransform(DCT)ofJPEG.Itusesasophisticatedcodingmechanismthatsupportsflexible,finelyembeddedrepresentationoftheimagesothatmanydesirablefeaturesareprovidedinonesinglebitstream.JPEG2000placesstrongemphasisonscalabilitytotheextentthatvirtuallyallJPEG2000bitsreamsarehighlyscalable.Thispapergivesanoverviewofthistriumphininnovationsandteamwork.Itgivesbriefintroductionstothefournewparts:①InteractiveTools,ApplicationProgrammingInterfaces,andProtocols(JPIP)；②SecureJPEG2000(JPWL)；③3-DData(JP3D)；④

Wireless(JPWL)thatareundercurrentlydevelopmentbytheJPEGcommittee.ItattemptstosummarizethelessonslearnedfromtheJPEG2000developmentexperienceanddrawsomeconclusionsonthesuccessfactorsofthisimportantstandard.

2．DevelopmentofJPEG2000

1)

OriginalJPEG

TheoriginalJPEGstandard,whichwasdevelopedinthelate1980s,isaverysuccessfulstandardintermsofitswidespreadusebyverylargenumberofdigitalimagingapplications.ThetechnologyadoptedinbaselineJPEGatthetimeofitsdevelopmentwasbasedonasimple,efficient8-by-8DCTcompressionalgorithmthatusesHuffmancoding,operatedinsequentialmodeandrestrictedto8-b/pixelinput.Besidesitstechnicalmerits,thesuccessenjoyedbyJPEGcanbeattributedtotheavailabilityofthefreeandefficientsoftwaredevelopedbytheIndependentJPEGGroup(IJG).PartofthesuccessofJPEGwasduetotheintroductionoftheJFIFfileformatthatmakesthepopularfileextension(image.jpg),whichissynonymouswithJPEGcompressedimages,ubiquitousinimagingapplications.Interestingly,theJFIFfileformatwasnotpartoftheoriginalJPEGstandard,asthecommittee’sgoalwastostandardizeasetofcompressiontools,andtheimportanceofaninterchangefileformatwasonlyrealizedasanafterthought.WewillseethatinthedevelopmentofJPEG2000,specialimportancewasgiventothedevelopmentoftherelevantfileformatssothatimagingapplicationswiththegreatestsystemsfunctionalitiescanbeaccomplished.

OtherimagefileformatsthatuseJPEGasthebasecompressiontechnologyhavebeendevelopedbytheindustryinthe1990stosatisfytheneedsofdifferentimagingapplications.Amongthem,theEXIFfileformat,usedinthemajorityofdigitalcameras,wasdesignedtoincludethemetadataassociatedwithaJPEGcompresseddigitalimage.TIFF/EPisanotherstandardthatprovidesamethodtoencapsulateJPEGimageswithrelevantmetadata.

Besidestheneedforhandlingmetadata,theneedtodeliververyhighresolutionimagesovertheInternetalsomotivatethedevelopmentoftheFlashPixfileformatinthemid-1990s.FlashPixisaJPEG-basedmultiresolutiontiledimagefileformatthatallowsimagestobestoredatdifferentresolutionsforcommonapplicationsinofficesandhomes,suchaseditingorprinting.ThedevelopmentofFlashPix,whichwasprimarilydrivenasanindustryconsortiumstandardbyagroupofcompanies(Hewlett-Packard,Kodak,Microsoft,andLivePicture),illustratesthedifferentapproachestakenindevelopmentstandardswithdifferentoutcomes.

2)

MotivationforJPEG2000

DespitethesuccessofJPEGinthe1990s,agrowingnumberofnewapplicationssuchashigh-resolutionimagery,digitallibraries,high-fidelitycolorimaging,multimediaandinternetapplications,wireless,medicalimaging,etc.,requireadditional,enhancedfunctionalitiesfromacompressionstandardthatJPEGcannotsatisfyduetosomeofitsinherentshortcomingsanddesignpointsthatwerebeyondthescopeofJPEGwhenitwasdevelopedinthepreviousdecade[2].TheshortcomingsofJPEGcanbeseeninanumberofareas:distortionandartifacts,ineffectivehandlingofhigh-qualityimages,poorcompressionforlosslessimages,lackofeffectivecolor-spacesupport,andlackofresolutionscaling.DistortionandartifactsintroducedbyJPEGincompressionlargeimages,especiallyathighcompressionrates,manifestinthewellknownblockingortilingartifactswhereeach8-by-8-pixelregiondevelopedwell-definededges,andringingartifactswheresmallwavesappearnexttosharpedgesintheimage.ThelimitationofJPEG’s64-kilopixelsampleshaveproventobetoorestrictiveformanynewimagingapplicationssuchasmedicalandhigh-resolutionimagery.Thelackofeffectivecolor-spacesupportinJPEGseverelyhindersitsadoptioninprepressandothergraphicsartsapplicationswhereconsistentcolorinformationfromimagecapturetoediting,display,orprintinghastobetightlymanaged[3].Finally,poorcompressionforlosslessimagesisalsoseenasalimitationbecausethelosslessmodeinJPEGisaccomplishedbyacompletelydifferentmethodthanthelossymode,andmovingfromonetotheotherrequirescompletelydecodingandrecodingtheimage.

WhiletheextendedJPEGsystems(suchasFlashPixandotherproprietaryfileformats)couldaddresssomeoftheseshortcomings,theirresultsweremixedandwidespreadadoptionswerenotseen.SomeofthesesolutionsweredrivenbyindustryconsortiathatareoperatingbasedonbusinessneedsasthefirstobjectiveandlackedthewidereachingdevelopmentprocessofaformalstandardsapproachsuchastheISOstandardizationprocess.Othersolutionsthatweredrivenbyproprietarytechnologiesbysinglecompanyaretiedtoparticularproductsthatoftenresultedinlimitedmarketadoption.

Inthemid-1990s,theJPEGcommitteehadanopportunitytostartanewworkitemtoaddresstheseissues,andtheresultistheJPEG2000familyofimagecodingstandards.

3)

DevelopmentofJPEG2000

AtthetimeofthecompleteoftheJPEGseriesofimagecompressionstandard(ISO/IEC10918-1to4)intheearly1990s,theJPEGcommitteeaddedanewprojectthataimedforthelosslessandnear-losslesscompressionofcontinuous-tonestillimagestoaddresstheinadequateperformanceofJPEG.TheresultofthatactivitywasthepublicationoftheISO/IEC14495ITU-TT.87standard,calledJPEG-LS,whichofferedanewimprovedmethodforcodingphotographicimageswithoutloss,orwithwell-defineddistortion,whichisveryusefulinmedicalimagingandotherswheremanyeditsmaybeexpectedofanoriginalimage.OutofthemanysubmissionsforJPEG-LStechnology,therewasawavelet-basedtechnologysubmittedbyRicohcalledCREWthatprovided,inasinglecompressedbit-stream,acontinuouslosslesstolossycompressionscheme.EventhoughCREWwasnotadoptedasthetechnologyforJPEG-LS,theinterestingsetoffeaturesthatCREWillustratedwasverymuchappreciatedbythecommittee.Subsequentlyanewnetworkitemforanewcompressionsystem(latercalledJPEG2000)wasestablished,thatkick-startingtheJPEG2000project.

InMarch1997,acallforproposalswasissuedseekingtoproduceastandardto“addressareaswherecurrentstandardsfailedtoproducethebestqualityorperformance,”“providecapabilitiestomarketsthatcurrentlydonotusecompression,”and“provideanopensystemapproachtoimagingapplications.”Inadditiontothecallforcontributions,theJPEGcommitteereleasedasetof40testimagestobeprocessedandsubmittedforevaluation.InNovember1997,morethan20algorithmsweresubmittedandevaluatedbytheJPEGcommittee.Awavelet-basedcompressionmethodwasadoptedasthebackboneofthenewstandard.Acomprehensiverequirementsdocumentwasdevelopedthatdefinedalltheapplicationareasofthestandardalongwithasetofmandatoryandoptionalrequirementsforeachapplication[4].InMarch1998,thefirstversionofareferencetestenvironmentcalledtheJPEG2000VerificationModel(VM)wasestablished.InDecember2000,afterthreeyearsofdedicatedworkbyover100JPEGexpertsfromover18nationalbodies,conductinghundredsoftechnicalstudiesknownascoreexperiments,Part1oftheJPEG2000standardfinallyreachedInternationalStandardstatus.

ThepublicationofJPEG2000isatriumphofinnovationsandteamworkinformalstandardprocesswherethebestmindsinimagecompressiontechnologygatheredfromallovertheworldtoworkonaconsensusdrivenprocessandcomeupwiththespecificationofthemostcomprehensiveimagecodingsystemthatwilllastthroughtheendofthisdecade.

NEWWORDSANDPHRASES

auspices n. 由……主辦或支持

scalability n. 可量測(cè)性

triumph n. 成功，勝利

baseline n. 基線

ubiquitous adj. 到處存在的，普遍存在的

afterthought n. 事后產(chǎn)生的想法，追悔，再思

metadata n. 元數(shù)據(jù)

consortium n. 社團(tuán)，協(xié)會(huì)，聯(lián)盟

high-fidelity 高保真度

artifacts n. 假象

restrictive adj. 限制性的

address vt. 處理；對(duì)付

proprietary adj. 專利的(所有的)

continuous-tone adj. 連續(xù)色調(diào)的

still adj. 靜態(tài)的

wavelet n. 小波，微波

NOTES

[1]Thestandardmakesuseofseveralrecentadvancesincompressiontechnologytodeliversuperiorcompressionperformanceandprovidesmanyadvancedfeaturesinscalability,flexibility,andsystemsfunctionalitiesthatoutperformitspredecessor,theoriginalJPEGstandard.

本句是個(gè)較復(fù)雜的并列長(zhǎng)句?！癿akesuseof”和“provides”作“thestandard”的并列謂語(yǔ)，其余都是其復(fù)合賓語(yǔ)?！皌odeliversuperiorcompressionperformance”是目的狀語(yǔ)?！癷nscalability,flexibility,andsystemsfunctionalitiesthatoutperformitspredecessor,theoriginalJPEGstandard.”是“features”的方式狀語(yǔ)，“that”引導(dǎo)了一個(gè)后置定語(yǔ)從句，用來(lái)修飾“functionalities”。

本句可譯為：此標(biāo)準(zhǔn)利用了幾種圖像壓縮新技術(shù)來(lái)獲得更好的壓縮性能，并且在可伸縮性、靈活性和系統(tǒng)功能方面提供了許多高級(jí)特性，這些系統(tǒng)功能(性能上)超過(guò)了它前面的原始標(biāo)準(zhǔn)JPEG。

[2]DespitethesuccessofJPEGinthe1990s,agrowingnumberofnewapplicationssuchashigh-resolutionimagery,digitallibraries,high-fidelitycolorimaging,multimediaandinternetapplications,wireless,medicalimaging,etc.,requireadditional,enhancedfunctionalitiesfromacompressionstandardthatJPEGcannotsatisfyduetosomeofitsinherentshortcomingsanddesignpointsthatwerebeyondthescopeofJPEGwhenitwasdevelopedinthepreviousdecade.這是一個(gè)比較復(fù)雜的長(zhǎng)句。“require”的主語(yǔ)是“agrowingnumberofnewapplications”，賓語(yǔ)是“additional,enhancedfunctionalities”?！皌hatJPEGcannotsatisfyduetosomeofitsinherentshortcomingsanddesignpointsthatwerebeyondthescopeofJPEGwhenitwasdevelopedinthepreviousdecade.”是一個(gè)后置定語(yǔ)從句，修飾前面的“acompressionstandard”。“thatwerebeyondthescopeofJPEGwhenitwasdevelopedinthepreviousdecade.”是修飾“designpoints”的后置定語(yǔ)從句。本句可譯為：盡管JPEG在20世紀(jì)90年代是成功的，但是越來(lái)越多的新應(yīng)用，比如高清晰度圖像、數(shù)字圖書(shū)館、高保真彩色圖像、多媒體和互聯(lián)網(wǎng)應(yīng)用、無(wú)線和醫(yī)學(xué)圖像等需要從壓縮標(biāo)準(zhǔn)中獲得額外的、增強(qiáng)的功能，但是JPEG不能滿足這些需求，原因在于JPEG內(nèi)在的缺點(diǎn)和某些要素超出了當(dāng)時(shí)它的設(shè)計(jì)范圍，而JPEG是在十年前開(kāi)發(fā)的。

[3]Thelackofeffectivecolor-spacesupportinJPEGseverelyhindersitsadoptioninprepressandothergraphicsartsapplicationswhereconsistentcolorinformationfromimagecapturetoediting,display,orprintinghastobetightlymanaged.

“whereconsistentcolorinformationfromimagecapturetoediting,display,orprintinghastobetightlymanaged.”是狀語(yǔ)從句，進(jìn)一步解釋“othergraphicsartsapplications”。本句可譯為：對(duì)彩色空間有效支持的缺乏嚴(yán)重阻礙了JPEG在預(yù)壓縮和其他形象藝術(shù)運(yùn)用方面的應(yīng)用，在這些應(yīng)用中，從圖像捕捉到編輯、顯示或打印的一致性色彩信息不得不嚴(yán)格進(jìn)行限制管理。

[4]Acomprehensiverequirementsdocumentwasdevelopedthatdefinedalltheapplicationareasofthestandardalongwithasetofmandatoryandoptionalrequirementsforeachapplication.“that”引導(dǎo)了一個(gè)定語(yǔ)從句，修飾補(bǔ)充“document”。“and”表示前后兩個(gè)短語(yǔ)是“defined”的并列賓語(yǔ)。

本句可譯為：(JPEG委員會(huì))開(kāi)發(fā)了一個(gè)全面的必需文件，在文件中定義了標(biāo)準(zhǔn)的所有應(yīng)用領(lǐng)域及每個(gè)應(yīng)用所需的強(qiáng)制性和可選的要求。

EXERCISES

Ⅰ.Translatethefollowingwordsorphrases.

JPEG imagefileformat high-resolution

high-fidelity imagecompressiontechnology

無(wú)損壓縮內(nèi)在缺點(diǎn) 靜止圖像

Ⅱ.TranslatethefollowingparagraphsintoChinese.

(1)

DistortionandartifactsintroducedbyJPEGincompressionlargeimages,especiallyathighcompressionrates,manifestinthewellknownblockingortilingartifactswhereeach8-by-8-pixelregiondevelopedwell-definededges,andringingartifactswheresmallwavesappearnexttosharpedgesintheimage.

(2)

WhiletheextendedJPEGsystems(suchasFlashPixandotherproprietaryfileformats)couldaddresssomeoftheseshortcomings,theirresultsweremixedandwidespreadadoptionswerenotseen.SomeofthesesolutionsweredrivenbyindustryconsortiathatareoperatingbasedonbusinessneedsasthefirstobjectiveandlackedthewidereachingdevelopmentprocessofaformalstandardsapproachsuchastheISOstandardizationprocess.

(3)

InMarch1997,acallforproposalswasissuedseekingtoproduceastandardto“addressareaswherecurrentstandardsfailedtoproducethebestqualityorperformance,”“providecapabilitiestomarketsthatcurrentlydonotusecompression,”and“provideanopensystemapproachtoimagingapplications.”Inadditiontothecallforcontributions,theJPEGcommitteereleasedasetof40testimagestobeprocessedandsubmittedforevaluation.InNovember1997,morethan20algorithmsweresubmittedandevaluatedbytheJPEGcommittee.Awavelet-basedcompressionmethodwasadoptedasthebackboneofthenewstandard.

參考譯文

第八單元JPEG2000：回顧和新發(fā)展

1．簡(jiǎn)介

JPEG2000是一個(gè)在ISO/IECJTC1/SC29/WG1(通常稱為聯(lián)合圖像專家組JPEG委員會(huì))支持下新開(kāi)發(fā)的圖像壓縮標(biāo)準(zhǔn)。此標(biāo)準(zhǔn)利用了幾種圖像壓縮新技術(shù)來(lái)獲得更好的壓縮性能，并且在可伸縮性、靈活性和系統(tǒng)功能方面提供了許多高級(jí)特性，這些系統(tǒng)功能(性能上)超過(guò)了它前面的原始標(biāo)準(zhǔn)JPEG。特別的是，JPEG2000使用離散小波變換(DWT)代替了JPEG中的離散余弦(DCT)變換。它使用了一種復(fù)雜的編碼機(jī)制，這種機(jī)制比較靈活，且能更好地表現(xiàn)內(nèi)部圖像特點(diǎn)，這樣在單個(gè)的比特流中就可提供許多想要的圖像特性?？缮炜s性是JPEG2000特點(diǎn)的重中之重。事實(shí)上在某些方面，所有的JPEG2000比特流都是具有高度可伸縮性的。本文對(duì)它在技術(shù)創(chuàng)新和協(xié)作方面的成功進(jìn)行評(píng)論，主要從四個(gè)新的部分進(jìn)行介紹：①交互式工具，應(yīng)用編程接口和協(xié)議(JPIP)；②可靠的JPEG2000(JPWL)；③3-D數(shù)據(jù)(JP3D)；④JPEG委員會(huì)正在開(kāi)發(fā)的無(wú)線部分(JPWL)。本文試圖總結(jié)JPEG2000開(kāi)發(fā)過(guò)程中的教訓(xùn)，并得出這個(gè)重要標(biāo)準(zhǔn)開(kāi)發(fā)成功的一些結(jié)論。

2．JPEG2000的發(fā)展過(guò)程

1)原始JPEG

原始JPEG標(biāo)準(zhǔn)開(kāi)發(fā)于20世紀(jì)80年代后期，已被廣泛使用在大量數(shù)字圖像應(yīng)用中。從應(yīng)用的范圍來(lái)說(shuō)，它是一個(gè)很成功的標(biāo)準(zhǔn)。開(kāi)發(fā)基本JPEG標(biāo)準(zhǔn)時(shí)采用的是基于8

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8離散余弦變換(DCT)的壓縮算法，這種算法簡(jiǎn)單有效，以順序的方式使用哈夫曼編碼，把輸入限制在每像素8

bit以內(nèi)。除了這些技術(shù)優(yōu)點(diǎn)，JPEG的成功可歸功于它使用了免費(fèi)而高效的軟件，這個(gè)軟件是由獨(dú)立的JPEG組織(IJG)開(kāi)發(fā)的。JPEG標(biāo)準(zhǔn)成功的部分(原因)是由于JFIF文件格式的引入，這種格式使得.jpg擴(kuò)展名流行于世，并與JPEG壓縮圖像同義，在圖像應(yīng)用中到處存在。有趣的是，JFIF文件格式并不是原始JPEG標(biāo)準(zhǔn)的一部分。因?yàn)槲瘑T會(huì)的目的是標(biāo)準(zhǔn)化一系列的壓縮工具，而交換文件格式僅僅是事后的想法。我們將看到在JPEG2000的發(fā)展中，在相關(guān)文件格式的開(kāi)發(fā)上給予了特別的重視，所以擁有最大系統(tǒng)功能的成像應(yīng)用就能使用這種格式了。

20世紀(jì)90年代，為了滿足不同的圖像應(yīng)用，開(kāi)發(fā)了其他的使用JPEG作為基本壓縮技術(shù)的圖像文件格式。在這些文件格式中，EXIF格式是應(yīng)用在大多數(shù)數(shù)碼相機(jī)中的一種數(shù)據(jù)格式，它被設(shè)計(jì)成能夠壓縮與JPEG圖像相關(guān)的元數(shù)據(jù)。TIFF/EP是另一種能把JPEG圖像和相關(guān)元數(shù)據(jù)壓縮在一起的標(biāo)準(zhǔn)。除了處理元數(shù)據(jù)的需求，在20世紀(jì)90年代中期，能在互聯(lián)網(wǎng)上傳輸高分辨率的圖像的需求也推動(dòng)了FlashPix文件格式的開(kāi)發(fā)。FlashPix是一個(gè)基于JPEG的多分辨率平鋪圖像文件格式。對(duì)辦公室和家庭的編輯與打印通用應(yīng)用來(lái)說(shuō)，這種文件格式允許圖像被存儲(chǔ)成不同的分辨率(的文件)。FlashPix文件格式(的開(kāi)發(fā))主要受到部分公司組成(Hewlett-Packard、Kodak、Microsoft和LivePicture)的工業(yè)聯(lián)盟標(biāo)準(zhǔn)的推動(dòng)，它的開(kāi)發(fā)表明：對(duì)開(kāi)發(fā)標(biāo)準(zhǔn)來(lái)說(shuō)，使用不同方法可以得到不同的成果。

2)開(kāi)發(fā)JPEG2000標(biāo)準(zhǔn)的動(dòng)機(jī)

盡管JPEG在20世紀(jì)90年代是成功的，但是越來(lái)越多的新應(yīng)用，比如高清晰度圖像、數(shù)字圖書(shū)館、高保真彩色圖像、多媒體和互聯(lián)網(wǎng)應(yīng)用、無(wú)線和醫(yī)學(xué)圖像等需要從壓縮標(biāo)準(zhǔn)中獲得額外的、增強(qiáng)的功能，但是JPEG不能滿足這些需求，原因在于JPEG內(nèi)在的缺點(diǎn)和某些要素超出了當(dāng)時(shí)它的設(shè)計(jì)范圍，而JPEG是在十年前開(kāi)發(fā)的。JPEG的缺點(diǎn)體現(xiàn)在很多地方：圖像的失真和假象，對(duì)高質(zhì)量圖像處理效率不高，無(wú)失真圖像壓縮性能較差，缺乏有效的彩色空間的支持以及缺乏分辨率的可伸縮性。在壓縮大幅圖像時(shí)，尤其是以高壓縮比壓縮圖像時(shí)，JPEG引入的圖像失真和假象在有名的塊或平鋪假象以及振蕩假象中體現(xiàn)得很明顯。在塊或平鋪假象中，每個(gè)8

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8像素區(qū)域開(kāi)發(fā)了已經(jīng)明確定義的邊緣，在振蕩假象中圖像中的小波顯示與尖銳的邊緣相鄰。已經(jīng)證明：JPEG的64k像素抽樣對(duì)很多新圖像應(yīng)用的限制非常大，這些應(yīng)用包括醫(yī)學(xué)和高分辨率肖像。對(duì)彩色空間有效支持的缺乏嚴(yán)重阻礙了JPEG在預(yù)壓縮和其他形象藝術(shù)運(yùn)用方面的應(yīng)用。在這些應(yīng)用中，從圖像捕捉到編輯、顯示或打印的一致性色彩信息不得不嚴(yán)格進(jìn)行限制管理。最后，性能較差的無(wú)損圖像壓縮也可以看做是一種局限，因?yàn)镴PEG中的無(wú)損壓縮模式是用一種完全不同于有損模式的方法來(lái)完成的，并且從一種模式轉(zhuǎn)換到另一種模式需要徹底地對(duì)圖像進(jìn)行解碼和再編碼。雖然擴(kuò)展的JPEG系統(tǒng)(比如FlashPix和其他的私有文件格式)能夠解決這些缺陷中的一些問(wèn)題，但是它們的結(jié)果是復(fù)合性的，并沒(méi)有得到廣泛的應(yīng)用。其中的一些解決方案是由工業(yè)協(xié)會(huì)所推動(dòng)的，這些協(xié)會(huì)的運(yùn)作把商業(yè)需要作為第一目標(biāo)，缺乏廣泛深入的、正常標(biāo)準(zhǔn)開(kāi)發(fā)所需的過(guò)程，比如ISO的標(biāo)準(zhǔn)化過(guò)程。另外一些解決辦法是由單個(gè)公司的專利技術(shù)所推動(dòng)的，這種公司依靠特別的產(chǎn)品生存，這常常導(dǎo)致解決辦法被限制在有限的市場(chǎng)中。

20世紀(jì)90年代中期，JPEG委員會(huì)迎來(lái)了一個(gè)解決這些問(wèn)題的機(jī)會(huì)，開(kāi)始了一個(gè)新的工作階段，產(chǎn)生了JPEG2000族圖像編碼標(biāo)準(zhǔn)。

3)

JPEG2000的開(kāi)發(fā)

20世紀(jì)90年代早期，在JPEG系列圖像壓縮標(biāo)準(zhǔn)完成的時(shí)候，JPEG委員會(huì)增加了一個(gè)新的項(xiàng)目。這個(gè)項(xiàng)目的目的是解決JPEG中對(duì)連續(xù)色調(diào)靜止圖像的無(wú)損和近無(wú)損壓縮的性能不佳的問(wèn)題。這個(gè)項(xiàng)目的結(jié)果是發(fā)布了ISO/IEC14495ITU-TT.87標(biāo)準(zhǔn)，稱為JPEG-LS，這個(gè)標(biāo)準(zhǔn)為無(wú)損的或帶有明確失真定義的照片圖像編碼提供了一個(gè)新的改良的方法，這種方法在醫(yī)學(xué)圖像和其他的對(duì)原始圖像編輯的應(yīng)用中非常有用。在很多JPEG-LS技術(shù)的意見(jiàn)書(shū)中，Ricoh提交了一種基于小波技術(shù)的、稱為CREW的意見(jiàn)書(shū)。這種CREW技術(shù)以一種單一的壓縮比特流提供一個(gè)從連續(xù)無(wú)損到有損壓縮的機(jī)制。盡管CREW沒(méi)有被JPEG-LS采用，但是它展現(xiàn)的特點(diǎn)受到了JPEG委員會(huì)的贊賞和關(guān)注。因此，(人們)為一個(gè)新的壓縮系統(tǒng)(后來(lái)稱為JPEG2000)建立了一個(gè)新的網(wǎng)絡(luò)項(xiàng)目，就此開(kāi)啟了JPEG2000計(jì)劃。

1997年3月，發(fā)布了一個(gè)旨在尋求制定一個(gè)“解決當(dāng)前標(biāo)準(zhǔn)不能產(chǎn)生最優(yōu)性能”的標(biāo)準(zhǔn)的建議，(號(hào)稱)“提供能力給當(dāng)前不能使用壓縮的市場(chǎng)”、“為成像應(yīng)用提供一個(gè)開(kāi)放的系統(tǒng)方法”。除了號(hào)召投稿外，JPEG委員會(huì)發(fā)布了一系列用來(lái)處理的40幅測(cè)試圖像，并號(hào)召提交評(píng)估報(bào)告。1997年11月，20多個(gè)算法被提交到了JPEG委員會(huì)，并進(jìn)行了評(píng)估。基于小波的壓縮方法被采用作為新標(biāo)準(zhǔn)的骨干技術(shù)。(JPEG委員會(huì))開(kāi)發(fā)了一個(gè)全面的必需文件，在文件中定義了標(biāo)準(zhǔn)的所有應(yīng)用領(lǐng)域及每個(gè)應(yīng)用所需的強(qiáng)制性要求和可選的要求。1998年3月，建立了一個(gè)稱為JPEG2000確認(rèn)模型(VM)的參考測(cè)試環(huán)境，這是它的第一個(gè)版本。2000年12月，在來(lái)自18個(gè)以上的國(guó)家團(tuán)體100多名專家3年的努力下，在做了數(shù)百次的技術(shù)研究(這些研究稱為核心實(shí)驗(yàn))后，JPEG2000標(biāo)準(zhǔn)的第一部分終于成為了國(guó)際標(biāo)準(zhǔn)。

JPEG2000標(biāo)準(zhǔn)的發(fā)布是創(chuàng)新和協(xié)作的勝利，這個(gè)協(xié)作是以正式的、標(biāo)準(zhǔn)的過(guò)程(來(lái)完成的)。(在此過(guò)程中)來(lái)自全世界的圖像壓縮技術(shù)(領(lǐng)域)的精英們?yōu)檫_(dá)成共識(shí)而奮斗，他們提出了大部分綜合性圖像編碼系統(tǒng)的規(guī)范，(這項(xiàng)工作)將會(huì)持續(xù)到這個(gè)十年的末期。

EXTENSIVETEXT

JPEG2000Algorithm

JPEG2000isdesignedtocomplimentthecurrentJPEGratherthanreplaceit.JPEGisbasedonnewtechnologiesandisdesignedfornewapplicationssuchascolorfacsimile,digitalimaging,remotesensing,medicalimagery,digitallibraries/archives,internet,e-commerce,printing,scanningetc.JPEG2000iswaveletbasedandcanbeimplementedinfixedpoint,floatingpointandintegerformats.Ithasbothreversible(lossless)andirreversible(lossy)modeswhichincludescorrespondingcomponenttransformations.

Fig8.1outlinestheencoder/de-coderoperationsofJPEG2000PartⅠ.

Thesecanbedescribedbrieflyasfollows.

Fig8.1JPEG2000Encoder/Decoder

1．DClevelshifting

AllcomponentvaluesareDClevelshiftedbysubtractingthesamequantity,iftheyareunsigned.

2．Componenttransformation(CT)

Twotypes：(i)irreversibleCT(ICT)usedforlossyorlosslesscoding；(ii)reversibleCT(RCT)usedonlyforlosslesscoding.FortheRCTallthreecomponents(RGB,YUV,YCbCretc.)shallhavethesamesamplingparametersandthesamehit-depth.

3.Tiling

Theimage(allthecomponents)isdividedintorectangularnonoverlappingequalsizeblocks(tiles)exceptattherightandlowerboundaries.Alloperationsincludingcomponentmixing,DWT,quantization,entropycodingetc.,areperformedindependentlyoneachfile.Tilingreducesmemoryrequirementsandenablesdecodingspecificpartsofanimage.

4．DWT

Thetilecomponentsaremappedintothewaveletdomainusingirreversible(Daubechies9/7filter)andreversible(5/3filter)transformations.Dyadicdecompositionoftheimagesusingthesefilterscanbeimplementedintwomodesi.e.,convolutionbasedandliftingbased.Forthelosslesscase,theliftingbasedfilteringforthe5/3analysisfilterisobtainedasfollows:

(1)

5．Quantization

Exceptforthelosslesscase(5/3

reversiblefilter)allDWTcoefficientsab(u,v)

arequantizedtoQb(u,v)

asfollows:

(2)

wherethestepsize

bisrepresentedrelativetothedynamicrangeofsubbandb,bytheexponientεb

andmantissaμbas

(3)

Thequantizedcoefficientsofsubbandsarecollectedintorectangulararraysof“codeblocks”.Theindividualbitplanesofthecoefficientsina“code-block”areentropycodedusingcontextbasedarithmeticcoding.Usingeither“Maxshift”or“scaling”method,certainregionsofinterest(ROI)canbecodedwithahigherqualitycomparedtothebackground.Markersareaddedtothebitstreamtoprovidequality(SNR)andresolution(spatial)scalabilities,errorresilienceandprogressivelossytolosslesscoding.TheentirebasicencodingoperationisbasedonEBCOT(embeddedblockcodingwithoptimizedtruncationoftheembeddedbitstreams).Inthis,thebitstrearnisorganizedasasuccessionoflayers.Foreachcodeblock,aseparatebitstreamisgeneratedindependently.Truncationpointstoeachcodeblockareallocatedusingratedistortioncriterion.Byapproximatelytruncatingeachcodeblock’sembeddedbitstream,specifictargetbitrate(distortionorquality)canbeachieved.

6．Region-of-interest(KOI)coding

JPEG2000providesthecapabilitytocodespecificregionsofinterest(R01)inanimageatahigherqualitycomparedtothebackground.Theseregionsaretransmittedfirstastheyhavehighpriority.InitiallyscalingbasedmethodinwhichcoefficientsrepresentingtheROIarescaledupwardsothattheirbitplanesareatahigherlevelcomparedtothoseofthebackground.Duringtheembeddedcodingprocess,ROImsbplanesareplacedfirstbeforethebitplanesrelatedtothebackground.Atthedecoder,theformerbitplanesarcdecoded/refinedbeforethebackground.Priortothisprocess,aROImaskrepresentingthesetofcoefficientsneedstobegenerated.AnextensionofthescalingbasedmethodistheMAXSHIFTmethodthatscalestheROIcoefficientswellabovethebackgroundcoefficientsthuseliminatingtheneedforgeneratingthemaskatthedecoder.TheMAXSHIFTmethodthusavoidsROIshape(mask)generation/encodingresultinginasimplerencoder/decoder.AdditionalimprovementsintheMAXSIIIFTmethodincludeinteractiveROIclient/serverselection.

7．Spatial/SNRscalabilities

JPEG2000providesbothspatialandSNR(quality)scalabilitieswhicharcimportantforinternetanddatabaseaccessapplicationsandbandwidthscalingforrobustdelivery(errorresil