Chapter 55-19The analog signal after correction is then converted into 8-bit digital signals that comply with the individual levels of pixel voltage by the A/D converter.5.3.7.5 Shading Correction (outline) 0013-8598Color iR C3380G / Color iR C2880G / Color iR C3380i / Color iR C3380 / Color iR C2880i / Color iR C2880 / iR C3480 / iR C3480i / iR C3080 / iR C3080i / iRC2550An original of even density does not necessarily mean uniform CCD output because of the following factors:(1) variation in the sensitivity of each pixel of the CCD(2) uneven intensity across the rod lens array(3) difference in intensity of light between the center and ends of the scanning lamp(4) deterioration of the scanning lampThe machine performs shading correction to correct any discrepancy in the output of the CCD. It performs shading correction at power-on and or for each job.5.3.7.6 Shading Adjustment 0013-8599Color iR C3380G / Color iR C2880G / Color iR C3380i / Color iR C3380 / Color iR C2880i / Color iR C2880 / iR C3480 / iR C3480i / iR C3080 / iR C3080i / iRC2550The machine measures the density of the standard while plate, and uses the result as density data. The data is then subjected to computation to obtain the targetvalue for use during shading correction.5.3.7.7 Shading Correction 0013-8600Color iR C3380G / Color iR C2880G / Color iR C3380i / Color iR C3380 / Color iR C2880i / Color iR C2880 / iR C3480 / iR C3480i / iR C3080 / iR C3080i / iRC2550The machine executes shading correction for each scan of the original. It measures the density of the standard white plate, and compares the measurement againstthe target value stored in the shading correction circuit; the machine then sets up the difference as the shading correction value, and uses it to correct any variationamong CCD pixel when scanning the originals, thus evening out the image density levels.F-5-32CCD outputOriginal densityStandard while plateCharacteristicsbefore correctionTarget valueMeasurementCharacteristicsafter correctionWhite
