Reader; Dadf - Canon F1 Service Manual

2
Technology > Controls > DADF > Original Scanning Assembly
● Dust Detection Control
Overview
The timing of dust detection is as follows.
Start key
ON
Before stream 1st sheet Between
reading scanned sheets
[1] [2] [3]
[1] White plate dust detection control
Steam reading glass / Scanning glass dust detection control,
[2]
Dust detection correction control (continuous lines)
[3] Dust detection correction control (noncontinuous lines)
- White plate dust detection
- Scanning glass dust detection
- Dust detection correction (continuous lines)
Scanner unit
- Dust detection correction (noncontinuous lines)

(DADF)

- White plate dust detection
Scanner unit
- Stream reading glass dust detection

(Reader)

- Dust detection correction (continuous lines)
- Dust detection correction (noncontinuous lines)
2 Technology > Controls > DADF > Original Scanning Assembly
2nd sheet
After scan Standby
scanned
[2] [3] [2]
F-2-68
White plate dust detection control
In this machine, the fans cool down the inside of the DADF to prevent the overheating at
stream reading operation. As a result, dust in the DADF may stick to the white plate and it
may cause the lines on the image.
To reduce the influence from the dust, the white plate dust detection and correction are
performed.
(1) White plate dust detection
The machine compares the shading coefficient obtained from shift shading and the shading
coefficient obtained from fixed shading to identify the presence/absence of dust and, if any,
identifies the coordinates and width of the area.
(2) White plate dust correction
If the machine detects the dust as a result of white plate dust detection, it interpolates the
shading coefficient of the area using the shading coefficient of both sides so as to decrease
the effects of the presence of dust. It executes the shading correction using the shading
coefficient obtained after the interpolation.
When the dust is detected as a result of white plate dust detection, the machine interpolates
the shading coefficient of the dust area using the shading coefficient of both sides so as to
reduce the effects of the dust. The shading correction is executed after the interpolation.
White plate
Area
of dust
Reference area
(Shading coefficient
F-2-69
computation area)
[Detection Algorithm]
Computation of shading Computation of shading
coefficient coefficient
(shift shading to (from fixed shading to
reference area) shading correction position)
Comparison
Detection of coordinates of
start of dust and width
[Correction Algorithm]
- Fixing shading
position
- Shading correction
Correction of dust area
position
coefficient using data of both sides
2-34
F-2-70
2-34