Ccd Drive; Gain Correction And Offset Correction Of The Ccd Output; A/D Conversion Of The Ccd Output; Shading Correction (Outline) - Canon iR3570 Service Manual

Chapter 5

5.3.6.2 CCD Drive

iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
The machine's CCD sensor 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 circuit board in parallel for each channel (total eight channels) of the CCD array.
CCD8 CCD7 CCD6
Light-receiving block
F-5-27

5.3.6.3 Gain Correction and Offset Correction of the CCD Output

iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
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).

5.3.6.4 A/D Conversion of the CCD Output

iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
The analog video signal is further converted into a digital signal that is suited to the voltage level of individual pixels by the A/D converter.

5.3.6.5 Shading Correction (outline)

iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
The output of the CCD is not necessarily even for the following factors even when the density of the original is uniform:
1) Variation in the Sensitivity Among Pixels of the CCD
2) Variation in the Intensity of the Rod Lens Array
The machine executes shading correction to even out the output of the CCD. Shading correction may be shading adjustment executed at power-on or shading cor-
rection executed for each job.

5.3.6.6 Shading Adjustment

iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
In this adjustment, the machine measures the density of the standard while plate, and stores the results in memory as density data. It then performs computations
on the shading data, and uses the result as the target value for shading correction.
5-14
Contact image sensor CIS)
CCD(1 line)
Analog
image
signal
CCD
drive control
Analog image
processing
A/D
-gain correction
conversion
-offset correction
CCD/AP circuit
CCD5 CCD2
output
L L H H L H L H H
Reader controller PCB
CCD
control signal
Gain
correction
CPU
data
Digital
image signal
Shading
correction
10
F-5-26
CCD1
H L
EEP-ROM
Target value
SRAM
J502
Digital
image signal
8
0006-5931
0006-5932
0006-5933
0006-5936
0006-5937