Seite - 180 - in Document Image Processing

J. Imaging 2017,3, 62 Figure9.Examplesof twoviewpointsof thesamedocument image, thatcouldbeused in thecontext ofcamera-baseddocument imageanalysis. 3.7.Nonlinear IlluminationModel DocCreatorprovidesanimplementationof thenonlinear illuminationmodelproposedin[52]. Whenscanningthickdocuments, thepagetobephotocopiedmaynotbeflatonthedocumentglass andthus the illumination isnotconstantonthewholedocument. Thismodelconsider thataborderof thedocument isbendinonedirectionbyaradiusρ. The illuminationatapointP’onthedocument pages is inverselyproportional to thedistanceofpointP’ fromthe lightsourceL.The illuminationat pointP’ is computedwith the followingequation: IP′= I0( l0 (l0+ρ(1−cosφ))) 2 where I0 is the original intensity, l0 thedistancebetween thedocument glass and the light source L, and φ the angle between the normal at P’ (where the page is curved) and the normal to the glassdocument. Figure10showsanexampleof this illuminationdefect. It isnoteworthy that this illuminationdefect simulates justaparticularcaseofwhatour3Dpaperdeformationmodelpresented in theprevioussectioncanportray. Except for the inkdegradationmodel, theotherdegradationmodelsworkbothongrayscaleand colourdocument images. DocCreatoraimsatprovidingotherdegradationmodels. Inparticular,wearecurrentlyworking onthe integrationofacolour inkspotgenerationmodeldescribed in [35]. 180