Canon imageRUNNER ADVANCE C350 series Service Manual page 61

2
Technical Explanation > Original Exposure and Feed System > Image Processing > Image Processing by the Main Controller PCB (Reader ASIC)
● Dust Detection Control
Overview
When an original is read in ADF mode, image correction or change in the original reading
position is performed depending on the presence of dust on the ADF Reading Glass, and a
control is executed by using the whiteness of the Platen Guide to prevent the dust from being
captured in the image.
The control of dust detection is as follows:
1) Dust detection correction control
2) Dust detection preventive process
Dust Detection Correction Control
When dust is detected on the ADF Reading Glass, the image is corrected so that the dust is
not captured.
Execution timing:
From when the original reaches the position immediately before reading until reading of the
original is finished (each page) in stream reading jobs
Executed behavior:
Dust correction
(1) The Platen Guide is read and any points
where dust may be adhered are detected
(2) The shadow that appears at the leading
edge of the original is detected
(3) Judgment of whether
to execute duct
correction
Necessary
Dust correction is executed
2 Technical Explanation > Original Exposure and Feed System > Image Processing > Image Processing by the Main Controller PCB (Reader ASIC)
Not necessary
Dust correction is not executed
F-2-22
1) Before the original is fed, the Platen Guide is read through the Reading Glass to detect
points where there is a possibility of dust.
2) The shadow that appears at the leading edge of the original is detected to detect the
leading edge of the original.
3) If no dust is found at the points of dust detected in step 1) after comparing the results of
dust detection before and after the shadow of the leading edge of the original appears on
the Reading Glass, it is judged to be dust on the Platen Guide, and thus no dust correction
is executed. If dust is found at the points detected in 1), it is judged to be dust on the
Reading Glass, and therefore dust correction is performed.
NOTE:
• Dust on the Platen Guide is hidden by paper, and does not affect images. Because of this,
dust correction is not performed.
• Dust on the Reading Glass affects images, and so dust correction is performed.
Size of dust that can be detected: 1 to 6 pixels
Number of dust locations that can be detected: 20 locations
Dust on the Platen Guide
Original
Dust on the Reading Glass
2-18
F-2-23
2-18