Seite - 34 - in Document Image Processing

J. Imaging 2018,4, 80 Aspreviouslymentioned, in thepast, educatedpersons tookspecial carewhenwriting, resulting in ahighdegreeof stability in the slant of theirwriting style. Thus, inorder todetect the slant of the text inahistoricaldocumentpage,a fewfragmentsof textareconsidered.Althoughonesample couldtheoreticallybeenough, severalonesare inpracticenecessary toensurecoverageofpageswith sparse textorspecial formatting, suchascolumns,arrays,etc. To localizeappropriate fragments the followingwayis followed: apage isscannedfromleft toright, toptobottomusingawindowofsize HxW (heightXwidth), startingfromthepixelposition(skip, skip) inorder toskipscanningorother noise. Skipcanbegeneral e.g., 1/5ofdocumentwidth (here), orbedetermineddependingon the collection.Allblackpixels (black_pixels) inside thewindowarecounted. Thearea inside thewindowis retained ifCondition (3) is trueandthescanningstopswhenthe requirednumberMof fragments is localized. black_pixels HxW >R (3) TheCondition (3) requires the text in thewindow to takeupmore thanR=0.10 of the area. Thesizeof thewindowintheseexperiments,HxW,wasselectedasH=2mbandW=7mb,where mbis themaincharacterbodysize in thepage(heightof thecharacterbodyexcludingascendersand descenders). In thecurrentpaper, the followingmetricsandparametersaresetup: 1. The text ratioR in thewindow; 2. TheamountMof the fragments inuse; 3. TheheightHof thewindow; 4. ThewidthWof thewindow. However, thesametechniquesareconsideredfor: 1. Themainbodyheightdetection[22], since itdoesnot require lineorwordsegmentation; 2. Theslantdetectionprocedure. Once theMfragmentshavebeenselected (Figure5), the slant detectionalgorithm[9],describedinSection2, isappliedandtheslantanglesaredetected,one per fragment. Themaximumandminimumslantanglesare ignoredaspossibleoutliers,while slant isdefinedas thedetected slantof thepage. Theentiredocumentpage is thencorrected accordingto theslantanglebyshiftingeachpixel so that xf = x0+round [ y0 tan ( π slant 180 )] (4) yf = y0 (5) where (x0,y0)defines the initialpositionof thepixeland(xf,yf) is thefinalpixelposition. 34