Ccd Output Gain Correction, Offset Correction; Ccd Output A/D Conversion; Outline Of Shading Correction; Shading Adjustment - Canon iR6570 series Service Manual

Light-receiving block

5.3.6.3 CCD Output Gain Correction, Offset Correction

The machine processes the analog video signals from the CCD so that the rate of their amplitude is a specific level. The machine also makes sure that the
output voltage in the absence of incident light is of a specific level (offset correction).

5.3.6.4 CCD Output A/D Conversion

The odd-numbered and even-numbered pixel analog video signals after correction are further converted into 10-bit digital signals representing specific
pixel voltage levels by the A/D converter.

5.3.6.5 Outline of Shading Correction

The machine executes shading correction so that the CCD output will be even when the density of the original is even.
The output of the CCD may not necessarily be even because of the following factors even if the density of the original is perfectly even:
1. variation in the sensitivity of the individual pixels of the CCD
2. difference in the degree of light passing through the center of the lens and through its edge
3. difference in the intensity of light between the center and ends of the scanning lamp
4. deterioration of the scanning lamp
The machine executes shading correction to make up for the variation in the output of the CCD.
Shading correction may be shading adjustment executed to determine a service mode target value or shading correction executed for every job.

5.3.6.6 Shading Adjustment

In shading adjustment, the machine measures the density of a white sheet of paper and the standard white plate, and stores the measurements in memory.
The machine then computes these measurements for use as the target value for shading correction. Shading adjustment is executed at time of machine
installation or scanning lamp replacement, or when a change has occurred in the intensity of light over time.
Service Mode:
COPIER>FUNCTION>CCD>CCD-ADJ

5.3.6.7 Shading Correction

The machine executes shading correction for every scan of an original.
The machine shines the light of the scanning lamp against the standard white plate, and measures the light reflected by the plate; it then uses the analog
image processing block of the CCD/AP PCB to turn the measurements into digital data, which will be sent to the shading correction circuit of the reader
controller PCB in the form of a shading coefficient.
In the shading correction circuit, the shading coefficient is compared against the target value stored in memory, and the machine uses the differences as
the shading correction value.
The shading correction value is used to make up for the variation among individual pixels of the CCD occurring at each scan, thus evening out the image
density level.
Shift register
Gate
6 5
(photo diode)
Shift register
Output buffer
Odd-numbered pixel data
4 3 2 1
Gate
Even-numbered pixel data
Output buffer
F-5-33
Chapter 5
0008-7516
0008-7517
0008-7518
0008-7519
0008-7520
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