Canon iR8500 Service Manual page 144

5.3 Digital Image Processing
5.3.1 Outline
Digital image processing is performed by the reader controller PCB, which has the fol-
lowing major functions:
[1] Shading correction
[2] Auto density adjustment (AE)
J6002
Gain/offset
correction data
CCD/AP
PCB
Even-number pixel
digital image signal
Odd-number pixel
digital image signal
5.3.2 Shading Correction
a. Outline
The output of the CCD will not necessarily be uniform because of the following factors
even if the density of the original in question is perfectly uniform:
1) The level of sensitivity of a CCD pixel differs from that of another.
2) The level of penetration of light differs between the center and the periphery of a lens.
3) The intensity of the scanning lamp differs between the middle and the ends of the
lamp.
4) The scanning lamp is subject to deterioration.
Shading correction is executed to correct discrepancies in the output of the CCD, and it
may be of either of the following two: shading adjustment used to determine a target level in
service mode and shading correction executed when scanning each original.
To make up for the fluctuations in the intensity of light occurring at short intervals, edge
area gain correction is also executed.
COPYRIGHT© 2001 CANON INC.
Reader controller PCB
J5003
Shading correction
8
Auto density
8
correction (AE)
F02-503-01 Functional Blocks
2000 2000 2000 2000 CANON iR8500/7200 REV.1 AUG. 2001
CHAPTER 2 NEW FUNCTIONS
EEP-ROM
Target
CPU
value
SRAM
Even-number pixel
digital image signal
Odd-number pixel
digital image signal
J5004
8
8
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