Driving The Ccd; Gain Correction And Offset Correction For The Ccd Output; A/D Conversion Of The Ccd Output; Shading Correction (Outline) - Canon iR C2880 Series Service Manual

(c) performs A/D conversion for the CCD output
(2) Digital image Processing
(a) performs shading correction
CCD (RGB, 1 line each)
Even-numbered
image processing
- gain correction
- offset correction

5.3.7.2 Driving the CCD

iR C3380i / iR C3380 / iR C2880i / iR C2880 / iR C3580 / iR C3580i / iR C3080 / iR C3080i
The machine's CCD sensor is a linear image sensor that consists of 3 lines (RGB, 1 line each), and it is composed of 7488-pixel photocells. The signals generated
through photo conversion at the light-receiving segment are sent as analog signals according to pixels in the order of G, B, and R.

5.3.7.3 Gain Correction and Offset Correction for the CCD Output

iR C3380i / iR C3380 / iR C2880i / iR C2880 / iR C3580 / iR C3580i / iR C3080 / iR C3080i
The analog video signal from the CCD is subjected to gain correction (in which the rate of amplification is corrected to a specific level) and offset correction (in
which the output voltage in the absence of incident light is also corrected to a specific level).

5.3.7.4 A/D Conversion of the CCD Output

iR C3380i / iR C3380 / iR C2880i / iR C2880 / iR C3580 / iR C3580i / iR C3080 / iR C3080i
The analog signal after correction is then converted into 8-bit digital signals that comply with the individual levels of pixel voltage by the A/D converter.

5.3.7.5 Shading Correction (outline)

iR C3380i / iR C3380 / iR C2880i / iR C2880 / iR C3580 / iR C3580i / iR C3080 / iR C3080i
An original of even density does not necessarily mean uniform CCD output because of the following factors:
(1) variation in the sensitivity of each pixel of the CCD
Contact image sensor (CIS)
Odd-numbered
pixel pixel
CCD drive control
Analog
image signal
Even-
numbered
Analog
pixel
A/D
conversion
Odd-
numbered
pixel
CCD/AP circuit
CCD16 CCD15 CCD14
R R R R
G G G G
B B B B
Single analog
shift register
Reader controller PCB
SCD control
signal
Line correction
data
Target
CPU
Digital
image signal
Shading
correction
10
F-5-30
CCD13 CCD2
R R R R R
G G G G G
B B B B B
output
G B R G B R G B R
F-5-31
EEP-ROM
value
SRAM
J203
Digital
image signal
8
CCD1
R R R
G G G
B B B
G B ......
Chapter 5
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