Seite - 32 - in Document Image Processing

J. Imaging 2018,4, 80 2.MaterialsandMethods 2.1. SlantDetectionAlgorithm Asalreadymentioned, in theproposedtechnique, theslantdetectionalgorithmthat ispresented indetail in [9] isused. Thereason is thatanalgorithmfor thedetection isneededandthisonehas provedtobepopularandsuccessful [3]. Thisspecificalgorithmmakesuseof thedifferencebetweentheascendersanddescenders. Incase the text isvertical, thedifference is larger (Figure3). Todetect that, ituses theWignerVilledistribution (WVD)[21], aspace-frequencydistributionofCohen’sclass,which isgivenbythe formula W(s, f)= +∞∫ −∞ z(s+τ/2)z∗(s−τ/2)e−2iπ fτdτ, (1) where s the signal, f the frequency, z(s) represents theanalytical signalassociatedwith thediscrete signalh(s), that in thepaper [9] is theverticalprojectionprofileof theword. Figure3.Fromleft toright: slantedwords, correspondinghistogramsandmaximumintensitycurves ofWVD(Wigner–Villedistribution). 32