A/D Conversion Of The Ccd Output - Canon iR4570 Series Service Manual

Chapter 5
level (offset correction).

5.3.6.4 A/D Conversion of the CCD Output

iR2270 / iR2870 / iR3570 / iR4570 / iR3530
The analog video signal is further converted into a digital signal that is suited to the voltage level of individual pixels
by the A/D converter.
5.3.6.5 Shading Correction (outline)
iR2270 / iR2870 / iR3570 / iR4570 / iR3530
The output of the CCD is not necessarily even for the following factors even when the density of the original is
uniform:
1) Variation in the Sensitivity Among Pixels of the CCD
2) Variation in the Intensity of the Rod Lens Array
The machine executes shading correction to even out the output of the CCD. Shading correction may be shading
adjustment executed at power-on or shading correction executed for each job.
5.3.6.6 Shading Adjustment
iR2270 / iR2870 / iR3570 / iR4570 / iR3530
In this adjustment, the machine measures the density of the standard while plate, and stores the results in memory as
density data. It then performs computations on the shading data, and uses the result as the target value for shading
correction.
5.3.6.7 Shading Correction
iR2270 / iR2870 / iR3570 / iR4570 / iR3530
The machine executes this correction for every scan made in main shading unit. It measures the density of the
standard white plate, and compares the result against the target value stored in the shading correction circuit; the
difference between the two will be held as the shading correction value for use in correcting variation among CCD
pixels when scanning the original, thus evening out the density levels of the image.
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