Seite - 178 - in Document Image Processing

J. Imaging 2017,3, 62 3.5.AdaptiveBlur Theblurdefect isaverycommondefectencounteredduringdigitizationcampaigns. Thedifficulty here is tocreatearealisticblurdefect thatmimics theveryslightblur thatappearswhenthescanner is incorrectlyset (a largeblur iseasilydetectedbyscanners). Todoso,weproposeamethodinspiredby theblurdetectionfrom[50]. First, theuserchoosesablur imagetomimicamongarealblurexample available inDocCreator. Then,usingadichotomicalgorithm,wecompute thesizeof thekernelof aGaussianblur that,onceappliedonthe input image,producesablursimilar to thechosenrealblur image. In thismethod, theFourierTransformof the image isfirst computed. Thenthemoduleof the FourierTransformisbinarizedaccordingto itsmean. Theresultingbinarized imageproducesadisc for imageswithonly text.As thehighfrequenciesdecreasewhentheblur increases, thedisc radius in thebinarized imagealsodecreaseswhen theblur increases. This radius isused tocharacterize the images. Thedichotomicalgorithmisusedtosearchthekernel size thatproducesaradiussimilar to theonefoundontheselectedexample image. SeeFigure7 foranexample. Figure 7. Adaptiveblurdefect. (Left) imagewith real blur. (Right) imagewith synthetic blur that mimics therealone 3.6. 3DPaperDeformation Thepaperonwhichabookisprintedmayhaveseveral typesofdeformation(alongcurvature, rotation, fold,hole, etc.).Weproposea3Ddeformationmodel thatgenerate realistic smallor large paperdeformations. Thefullprocessisdetailedin[51]. Themainideais: first,a3Dscannerisusedtoacquirea3Dmesh fromarealdocument. Thismeshpreservesall representativedistortions. Then, themesh isunfolded intoa2Dplan. Therefore,eachvertex in themeshhasacorresponding2Dpoint. Thecoordinatesof suchapoint are consideredas texture coordinates. Finally, themeshcanbe renderedwithany2D imagemappedasa texture. For therendering,weuse thePhongreflectionmodelas the illumination model. Changing lightproperties andpositionallows toaccentuateorminimizedistortioneffects. DocCreatorcurrentlyprovides17parameterizedmeshes, enablingone toproducenumerousdistorted images. Figure8showssuchadeformation. This3Dpaperdeformationmodelcanbeusedtosimulatemobiledocumentcapture. Theusercan addabackgroundplanewith texture,ontopofwhichthedocumentstands. Bychangingviewpoint andlightpositions, theusercangeneratemanyimages. These imagescanbeusedforcamera-based document imageanalysis. Figure9showsexamplesof twopointsofviewgeneratedwith thesame document image. 178