Canon Color Image Reader - L1 Service Manual

Also see for L1: Installation procedures Instructions

Canon Color Image Reader - L1 Service Manual Manual pdf 28 page image

2-172-1722 TechnologyTechnologyShading correctionOverviewThe output of the CMOS may not always be uniform because of the following reasons evenwhen the density of the original is uniform:Variation in the sensitivity among individual pixels of the CMOS.Difference in the level of transmission between the center and the edge of the lens.Difference in the intensity of light between the middle and the edges of the LED lamp unit.Deterioration of the LED lamp unit.The machine executes shading correction to even out the output of the CMOS.The machine executes either of the following 2 shading mechanisms: shading correctionthat is carried out per every copy and shading adjustment for which the target value is set inservice mode.Shading adjustmentThe machine performs shading adjustment in response to a command made in service mode.The machine computes the data entered in service mode to produce the target value for useat time of shading correction.Shading correctionThe machine executes shading correction each time it scans an original.The machine directs the light from the lamp unit against the standard white plate, and theanalog image processing block on the CMOS PCB converts the refl ected light into a digitalsignal. The result (i.e., a digital signal representing the intensity of the refl ected light) is sentto the shading correction circuit of the reader controller PCB as a shading coefficient. Theshading correction circuit in turn compares the coeffi cient with the target value it holds, andoffers the difference as the shading correction value.The machine uses the shading correction value to correct the variation that may exist amongthe individual pixels of the CMOS per each scan, thereby keeping the image density to aspecifi c level at all times.••••CMOS linesensor outputOriginal densityStandard white plateCharacteristics beforecorrectionTarget valueMeasurementCharacteristics aftercorrectionWhiteError codeE302 (Abnormality in the shading)-0001 Abnormality in the front side shading RAM access, value front side shading is below orabove the specification.-0101 Abnormality in the back side shading RAM access, value back side shading is below orabove the specification.