CHAPTER 2 FUNCTIONS & OPERATION
2. Shading
This section explains the reading
mechanism of the white reference sheet for
determination of the shading correction
value.
The sectional view of the reading unit is
shown below. Note that it is shown
horizontally for the description.
White
reference
sheet
White
reference
sheet
Figure 2-202
This machine can read the white
reference data at the document reading
position, unlike other scanners having the
black background color, since its
background color is white. Therefore, there
is neither need to feed the shading sheet
nor to move the internal white reference
sheet or the reading units.
For example, when the lower reading
unit reads the white reference data, the LED
emitted from the lower unit is reflected from
the white reference sheet on the upper unit
to be input to the sensor on the CIS PCB.
Since the white reference sheet is
placed under the reading glass, feeding
document does not cause dirt on it. Note
that executing shading while the reading
glass is dirty can cause poor images such
as white lines occurring in the images.
When this machine is turned ON or
starts scanning, it reads the white reference
data to determine the shading correction
value.
However, the slightly different optical
paths to the light receiving element are used
for the actual document and the white
reference sheet. Therefore this machine
needs fine adjustment of the shading
correction value using the service mode and
the shading sheet. This fine adjustment is
necessary after replacing the reading unit or
after replacing the control PCB recording
the shading correction value.
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©
CANON ELECTRONICS INC. 2011 CANON DR-C125 FIRST EDITION
2-7
