Image Processing; Overview - Canon iR6570 series Service Manual

The white plate can collect stray dust inside the reader unit, causing lines in images, and the machine is equipped with a mechanism to check for dust on
the plate and correct it to limit its effects on output images.
Timing of Control
1. Before a Job
- white plate dust detection
- white plate dust correction
2. After a Job
- white plate dust detection
- white plate dust correction
Particulars of Control
- White Plate Dust Detection
The machine compares the data on the light reflected by the white plate at time of fixed shading and shift shading to check for dust on the white plate while
at the same time identifying the coordinates and width of the area of dust.
- White Plate Dust Correction
If the machine detects the presence of dust, it corrects the shading correction coefficient of the area of dust by means of a correction coefficient used for
both sides of the area with dust, thus limiting the effects of the dust.
White plate data correction
area at time of shift shading

5.3.6 Image Processing

5.3.6.1 Overview

The PCBs used in the image processing system have the following functions:
CDD/AP PCB: CCD drive, analog image processing, A/D conversion
Reader controller PCB: shading correction
Start key
ON
1st
SCAN
Dust detection control
White plate
Data on light reflected
Dust
by the white plate
(shift shading))
Point of white plate data
measurement at time of fixed shading
2nd
SCAN
Dust detection control
F-5-28
Data on light reflected
by the white plate
(fixed shading)
Comparison
Identifies the coordinates
of the start of dust and width
Correction Algorithm
The machine corrects the correction
coefficient of the area of dust using data
for areas on both sides
F-5-29
Chapter 5
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