22 2-152-15Technology > Original Exposure System > Controls > Image ProcessingTechnology > Original Exposure System > Controls > Image ProcessingCMOS Sensor DriveThe CMOS sensor used in this machine is a 1-line linear image sensor consisting of 7488photocells. After completion of photoelectric conversion in the lightreceiving block, the signalsare output to the AP circuit in the reader relay PCB in parallel for each channel (total fourchannels) of the CMOS sensor array.CMOS sensor 1CMOS sensor 4 CMOS sensor 3HL L HH L HL H H L ………outputLight receiving blockCMOS Sensor Output Gain Correction and Offset CorrectionThe analog video signals output from the CMOS sensor are corrected so that they will havea specific gain level (gain correction), and the output voltages generated in the absenceof incident light are also corrected so that they it will have a specific offset level (offsetcorrection).CMOS Sensor Output A/D ConversionAfter completion of the above corrections, the analog video signals are converted to digitalsignals corresponding to individual pixel voltage levels by the A/D converter.F-2-28F-2-28Shading Correction (Outline)The CMOS sensor outputs are necessary even for the following reasons even when thedensity of the original is uniform:(1) Variation in sensitivity among CMOS sensor pixels(2) Variation in light intensity of rod lens arrayThe machine performs shading correction to even out the CMOS sensor output.There are two types of shading correction: shading adjustment performed in the Servicemode and shading correction performed for each job.Shading AdjustmentThe machine measures the density of the standard white plate, and stores the measureddensity data. It then processes the stored data to use it as the target value for shadingcorrection.Shading CorrectionThe machine performs shading correction for each scan. It measures the density of thestandard white plate, and compares the measured value with the target value stored in theshading correction circuit to use the difference between the two as the shading correctionvalue. The machine uses this shading correction value to correct the variation among CMOSsensor pixels when scanning the original, thus evening out the image density level.CMOSsensoroutputOriginal densityStandard white plateCharacteristicsbefore correctionTargetvalueMeasurementvalueCharacteristicsafter correctionWhiteF-2-29F-2-29
