Seite - 18 - in Document Image Processing

J. Imaging 2018,4, 27 capableoffiltering-outsuchanoise increasesenormously,asanewsetofhuesofpaperandprinting colorsappear. Thedirectapplicationofbinarizationalgorithmsmayyieldacompletelyunreadable document, as the interfering inkof the backside of thepaper overlapswith the binary one in the foreground. Severaldocument imagecompressionschemes forcolor imagesarebasedon“adding color” toabinary image. Suchcompressionstrategy isunable tohandledocumentswithback-to-front interference [5]. OpticalCharacterRecognizers (OCRs) are alsounable toworkproperly for such documents. Severalalgorithmsweredevelopedspecifically tobinarizedocumentswithback-to-front interference [3,4,6–9]. There isnobinarizationtechniquetobeanall casewinnerasmanyparameters mayinterfere inthequalityof theresultingimage[9]. Thedevelopmentofnewbinarizationalgorithms is still an important research topic. International competitionsonbinarizationalgorithms, suchas DIBCO-Document ImageBinarizationCompetition [10], areanevidenceof therelevanceof thisarea. Figure1. Imageswithback-to-front interference fromthe three test setsused in thispaper:Nabuco bequest (left),LiveMemory(center) andDIBCO(right). This paper presents a new global filter [1] to binarize documents, which is able to remove the back-to-front noise in awide range of documents. Quantitative and qualitative assessments made inawidevarietyofdocuments fromthreedifferent“real-world”datasets (typed,printedand handwritten, using different kinds of paper, ink, etc.) allow to witness the efficiency of the proposedscheme. 2.TheNewAlgorithm Thealgorithmproposedhere isperformedinfoursteps: 1. decision-makingforfindingthevector ofparametersof the imagetobefiltered,2. filteringthe imageusingabilateralfilter,3. splittingthe image into theRGBcomponents, andperformingtheirbinarizationusingamethodinspiredbyOtsu’s algorithm for eachRGB channel, and 4. choice ofwhich of theRGB components best preserved thedocument information in the foreground,which isconsideredthefinaloutputof thealgorithm. Figure 2presents theblockdiagramof theproposedalgorithm. The functionalityof eachblock is detailedas follows. 18