Image Processing; Overview; Ccd Drive; Gain Correction And Offset Correction Of Ccd Output - Canon iR3245 Series Service Manual

Chapter 5

5.3.6 Image Processing

5.3.6.1 Overview

iR3225 / iR3225N / iR3235 / iR3235N / iR3245 / iR3245N
The functions of image processing system's PCB are described below.
- Reader controller PCB
- CCD PCB
The machine uses the reader controller PCB to process images for every single image line. Specific functions are as follows.
1) CCD PCB (inside CCD unit)

- CCD drive

- CCD output gain correction, offset correction
2) Reader controller PCB
- Shading correction
5.3.6.2 CCD Drive
iR3225 / iR3225N / iR3235 / iR3235N / iR3245 / iR3245N
The machine's CCD sensor is a 4-line linear image sensor consisting of 7500 pixels. After completion of photoelectric conversion in the light-receiving block, the
signals are output to the analog front end PCB unit on CCD PCB in parallel for each channel (R, G, B, B/W) of the CCD array.

5.3.6.3 Gain Correction and Offset Correction of CCD Output

iR3225 / iR3225N / iR3235 / iR3235N / iR3245 / iR3245N
The analog video signal generated by the CCD is corrected so that it will have a specific level (gain correction); moreover, the output voltage occurring in the ab-
sence of incident light is also corrected so that it will have a specific level (offset correction).
5-18
CCD drive, analog image process, A/D conversion, shading correction (executed per each job), shading adjustment (executed at
power-on)
Analog image process, A/D conversion
CCD PCB
CCD(4lines )
Analog image
signal
CCD drive
control
Analog image
A/D
process
conversion
- gain correction
- offset
correction
CCD/AP PCB
Light-receiving block
Reader controller PCB
CCD
ASIC
control
signal
Gain
correction
data
CPU
Digital
image
signal
Shading
correction/
adjustment
F-5-27
Red(R)line
Green(G)line
Blue(B)line
Black & white(B/W)line
Expanse
Output
L L H H L H L H H H L
F-5-28
EEP- ROM
SRAM
Digital image J1
signal
0019-4661
0019-4662
0019-4663