Digital Image Processing; Outline; Shading Correction - Canon iR2200 Service Manual

CHAPTER 3 IMAGE PROCESSING SYSTEM

3 Digital Image Processing

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)
Reader controller PCB
Analog
image
processing
block
3.2 Shading Correction
3.2.1 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.
3-4 R
COPYRIGHT © 2001 CANON INC.
Gain/offset
correction data
· Shading correction
digital image
· Auto density
signal
correction (AE)
8
· Serial/parallel
conversion
F03-301-01
EEP-ROM
Target
CPU
value
Even-number
pixel
digital image
signal
Odd-number
pixel
2000 2000 2000 2000 CANON iR2200/iR2800/iR3300 REV.0 MAR. 2001
SRAM
J409
8
8