Canon iR2018 Series, Руководство по обслуживанию

Страница: 114 / 348

Chapter 4
4-14
Functions of the image processing system are summarized below.
T-4-7
The reader controller PCB is used to process images on a line-by-line basis. Its major functions are as follows:
1)Analog image processing
- CMOS sensor drive
- CMOS sensor output gain correction and offset correction
- CMOS sensor output A/D conversion
2)Digital image processing
- Shading correction
F-4-26
4.3.6.2 CMOS Sensor Drive
0017-2637
The CMOS sensor used in this machine is a 1-line linear image sensor consisting of 7488 photocells. After completion of photoelectric conversion in the light-
receiving block, the signals are output to the AP circuit in the reader controller PCB in parallel for each channel (total four channels) of the CMOS sensor array.
F-4-27
4.3.6.3 CMOS Sensor Output Gain Correction and Offset Correction
0017-2638
The analog video signals output from the CMOS sensor are corrected so that they will have a specific gain level (gain correction), and the output voltages generated
in the absence of incident light are also corrected so that they it will have a specific offset level (offset correction).
4.3.6.4 CMOS Sensor Output A/D Conversion
0017-2639
After completion of the above corrections, the analog video signals are converted to digital signals corresponding to individual pixel voltage levels by the A/D
converter.
4.3.6.5 Shading Correction (Outline)
0017-2640
The CMOS sensor outputs are necessary even for the following reasons even when the density of the original is uniform:
(1) Variation in sensitivity among CMOS sensor pixels
(2) Variation in light intensity of rod lens array
The machine performs shading correction to even out the CMOS sensor output.
There are two types of shading correction: shading adjustment performed in the Service mode and shading correction performed for each job.
- Reader controller PCB CMOS sensor drive, analog image processing, A/D
conversion, and shading correction
Target
value
CMOS sensor (1 line)
Analog image signal
Analog image
processing
- Gain correction
- Offset correction
A/D
conversion
CMOS sensor
drive control
CMOS sensor
control signal
Gain
correction
data
Digital
image
signal
IC1
10
Digital image
signal
8
Reader controller PCB
Contact image sensor (CIS)
J309
RAM
Shading correction
IC2
Serial
communication
I/F
CMOS sensor 1 CMOS sensor 4 CMOS sensor 3
H L L H H L H L H H L
output
Light receiving block