Canon iR3245, Service Manual

Page: 173 / 746

Chapter 5
5-17
5.3.5.2 White Board Dust Detection Control
0019-4653
iR3225 / iR3225N / iR3235 / iR3235N / iR3245 / iR3245N
When the dust in the air attaches to the white board inside the reader unit, lines may appear on the image. To reduce the influence from the dust, the machine carries
out the white board dust detection and correction.
[Control timing]
1. Before job
- White board dust detection
- White board dust correction
2. After job
- White board dust detection
- White board dust correction
F-5-25
[Particulars of control]
- White board dust detection
The machine compares the data of light reflected by the white plate at the shift shading and at the fixed shading to detect the presence/absence of dust, and if
any, it identifies the coordinates and width of dust.
- White board dust correction
If the machine detects dust as a result of white plate dust detection, it corrects the shading coefficient of the dust area using the shading coefficient of both sides
so as to decrease the effects of the dust.
F-5-26
Dust detection control
START key
ON
1st
SCAN 2nd
SCAN
Dust detection control
[Correction Algorithm ]
Shift shading
Data of light
reflected by
the white plate
Fixed shading
Data of light
reflected by
the white plate
Identifies the coordinates of
start and width of dust.
Corrects the shading coefficient of
dust area by using data of both sides.
Measurement position of
white board at fixed shading
Measurement position of white
board at shift shading
White plate
Dust area
Comparison