Canon Color Image Reader - L1 Service Manual

Also see for L1: Installation procedures Instructions

Canon Color Image Reader - L1 Service Manual Manual pdf 23 page image

2-122-1222 TechnologyTechnologyDust detection controlOverviewThe timing of dust detection is as follows.[2][1] [2] [2][3][3]Start keyONBefore streamreading1st sheetscanned2nd sheetscannedBetweensheets After scan Standby[1] White plate dust detection control[2] Steam reading glass / Scanning glass dust detection control,Dust detection correction control (continuous lines)[3] Dust detection correction control (noncontinuous lines)Scanner unit(DADF)- White plate dust detection- Stream reading glass dust detection- Dust detection correction (continuous lines)- Dust detection correction (noncontinuous lines)Scanner unit(Reader)- White plate dust detection- Scanning glass dust detection- Dust detection correction (continuous lines)- Dust detection correction (noncontinuous lines)White plate dust detection controlIn this machine, the fans cool down the inside of the DADF to prevent the overheating atstream reading operation. As a result, dust in the DADF may stick to the white plate and itmay cause the lines on the image.To reduce the infl uence from the dust, the white plate dust detection and correction are per-formed.(1) White plate dust detectionThe machine compares the shading coeffi cient obtained from shift shading and the shadingcoeffi cient obtained from fi xed shading to identify the presence/absence of dust and, if any,identifi es the coordinates and width of the area.(2) White plate dust correctionIf the machine detects the dust as a result of white plate dust detection, it interpolates theshading coeffi cient of the area using the shading coeffi cient of both sides so as to decreasethe effects of the presence of dust. It executes the shading correction using the shading coef-fi cient obtained after the interpolation.When the dust is detected as a result of white plate dust detection, the machine interpolatesthe shading coeffi cient of the dust area using the shading coeffi cient of both sides so as toreduce the effects of the dust. The shading correction is executed after the interpolation.[Detection Algorithm][Correction Algorithm]Computation of shadingcoefficient(shift shading toreference area)Computation of shadingcoefficient(from fixed shading toshading correction position)Detection of coordinates ofstart of dust and widthCorrection of dust areacoefficient using data of both sidesFixing shading positionShading correction positionReference area(Shading coefficientWhite plateAreaof dustComparison