Canon Color imageRUNNER C5180 Series, Руководство по обслуживанию

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Chapter 6
6-22
(2) Digital Image Processing
(a) Shading Correction
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6.3.6.2 CCD Drive
The machine's CCD is a linear image sensor consisting of 3 lines (R, G, B, 1 line each), each line composed of
7350 photo cells. The signal that has been put through photo-conversion in the light-receiving segment is
divided into 2 analog signals of 2 channels for output: even-numbered pixels (EVEN) and odd-numbered pixels
(ODD).
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6.3.6.3 CCD Gain Correction, Offset Correction
The analog video signal from the CCD is processed so that the rate of amplification is even (gain correction);
the output in the absence of incident light is also processed for a specific level (offset correction).
6.3.6.4 CCD Output A/D Conversion
The odd-numbered and even-numbered pixel analog video signals after the foregoing correction are then
converted into 10-bit digital signals by the A/D converter according to their pixel voltage levels.
6.3.6.5 Outline of Shading Correction
The output of the CCD may not always be uniform because of the following reasons even when the density of
the original in question is uniform:
- variation in the sensitivity among individual pixels of the CCD.
- difference in the level of transmission between the center and the edge of the lens.
- difference in the intensity of light between the middle and the edges of the scanning lamp.
- deterioration of the scanning lamp
The machine executes shading correction to even out the output of the CCD.
Gain correction
data
EEP-ROM
SRAM
CPU
Shading correction
Digital image
signal
CCD/AP
PCB
Reader controller PCB
10
Digital image
signal
8
Target
value
J101
J102
J204
J205
J203
Shift register
Light-receiving segment
(photodiode)
Shift register
Output buffer
Output buffer
Gate
Gate
1 2 3 4 5 6
Odd-numbered pixel data
Even-numbered pixel data