Canon iR7086, Service Manual

Page: 208 / 735

Chapter 5
5-22
F-5-52
5.3.6.5 CCD Output Gain Correction, Offset Correction
0011-2257
iR7105 / iR7095 / iR7086
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).
5.3.6.6 CCD Output A/D Conversion
0011-2258
iR7105 / iR7095 / iR7086
The odd-numbered and even-numbered pixel analog video signals after correction are further converted into 12-bit digital signals representing specific pixel voltage
levels by the A/D converter.
5.3.6.7 Outline of Shading Correction
0011-2259
iR7105 / iR7095 / iR7086
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.
5.3.6.8 Shading Adjustment
0011-2260
iR7105 / iR7095 / iR7086
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 ma-
chine then computes these measurements for use as the target value for shading correction. Shading adjustment is executed at time of machine installation or scan-
ning lamp replacement, or when a change has occurred in the intensity of light over time.
Service Mode:
COPIER>FUNCTION>CCD>CCD-ADJ
5.3.6.9 Shading Correction
0011-2261
iR7105 / iR7095 / iR7086
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.
F-5-53
Shift register
Light-receiving block
(photo diode)
Shift register
Output buffer
Output buffer
Gate
Gate
1 2 3 4 5 6
Odd-numbered pixel data
Even-numbered pixel data
CCD output
Original density
Standard white plate
Characteristics before
correction Target value
Measurement
Characteristics after
correction
White