Chapter 55-155.3.6.3 CCD Gain Correction, Offset Correction 0012-9686imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+The analog video signal from the CCD is processed so that the rate of amplification is even (gain correction); the output in the absence of incident light is alsoprocessed for a specific level (offset correction).5.3.6.4 CCD Output A/D Conversion 0012-9691imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+The odd-numbered and even-numbered pixel analog video signals after the foregoing correction are then converted into 10-bit digital signals by the A/D converteraccording to their pixel voltage levels.5.3.6.5 Outline of Shading Correction 0012-9692imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+The output of the CCD may not always be uniform because of the following reasons even when the density of the original in question is uniform:- variation in the sensitivity among individual pixels of the CCD.- 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 scanning lamp.- deterioration of the scanning lampThe machine executes shading correction to even out the output of the CCD.The machine executes either of the following 2 shading mechanisms: shading correction it carries out for every copy and shading adjustment for which the targetvalue is set in service mode.5.3.6.6 Shading Adjustment 0012-9693imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+The machine performs shading adjustment in response to a command made in service mode. The machine measures the density of blank white paper and that ofthe white plate to obtain density data; it then computes the data to produce the target value for use at time of shading correction.5.3.6.7 Shading Correction 0012-9694imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+The machine executes shading correction each time it scans an original.The machine directs the light from the scanning lamp against the standard white plate, and converts the reflected light into a digital signal by the analog imageprocessing block on the CCD/AP PCB. The result (i.e., a digital signal representing the intensity of the reflected light) is sent to the shading correction circuit ofthe reader controller PCB as a shading coefficient. The shading correction circuit in turn compares the coefficient against the target value it holds, and offers thedifference as the shading correction value.The machine uses the shading correction value to correct the variation that may exist among the individual pixels of the CCD, thereby keeping the image densityto a specific level at all times.F-5-35CCD outputOriginal densityStandard white plateCharacteristics beforecorrectionTarget valueMeasurementCharacteristics aftercorrectionWhite
