Cmos Sensor Drive; Cmos Sensor Output Gain Correction And Offset Correction; Cmos Sensor Output A/D Conversion; Shading Correction (Outline) - Canon iR2030 Series Service Manual

Chapter 4
Functions of the image processing system are summarized below.
- Reader controller PCB
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

4.3.6.2 CMOS Sensor Drive

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.

4.3.6.3 CMOS Sensor Output Gain Correction and Offset Correction

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

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)

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.
4-14
Contact image sensor (CIS)
CMOS sensor (1 line)
Analog image signal
IC1
Analog image
processing
A/D
- Gain correction
conversion
- Offset correction
CMOS sensor 4
Light receiving block
T-4-7
CMOS sensor drive, analog image processing, A/D
conversion, and shading correction
Reader controller PCB
CMOS sensor
Gain
drive control
correction
data
Target
value
RAM
Digital
image
signal
Shading correction
10
F-4-26
CMOS sensor 3
L L H H L H L
F-4-27
IC2
CMOS sensor
control signal
Serial
communication
I/F
J309
Digital image
signal
8
CMOS sensor 1
output
H H H L
0017-2637
0017-2638
0017-2639
0017-2640