Canon imageRUNNER C1335 Series Service Manual page 47

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Technical Explanation > Original Exposure and Feed System > Image Processing > Image Processing by the Main Controller PCB (Reader ASIC)
● Analog Control Performed by the CIS
The flow of analog image processing performed by the contact image sensor (CIS) is as
follows:
a. The light reflected by the original is collected by the rod lens array.
b. The light is received by the original scan sensor.
c. The original scan sensor converts the received light to an electric signal and outputs it.
d. Gain correction and offset correction of the Image Reading Sensor.
e. A/D conversion of the Image Reading Sensor.
The Image Reading Sensor consists of 12 sensors.
Each channel is provided with an output correction table to output an image signal after
performing gain correction for the input brightness signal.
● Original Reading Sensor Output Gain Correction and Offset
Correction
The analog video signals output from the original reading sensor are corrected so that they
will have a specific gain level (gain correction), and the output voltages generated in the
absence of incident light are also corrected so that they will have a specific offset level (offset
correction).
● Original Reading Sensor Output A/D Conversion
After completion of the gain correction and offset correction, the analog video signals are
converted to digital signals corresponding to individual pixel voltage levels by the A/D
converter.
2 Technical Explanation > Original Exposure and Feed System > Image Processing > Image Processing by the Main Controller PCB (Reader ASIC)
■ Image Processing by the Main Controller PCB (Reader ASIC)
● Outline of Shading Correction
The original reading sensor outputs are necessary even for the following reasons even when
the density of the original is uniform:
1) Variations in sensitivity of pixels of the Image Reading Sensor
2) Uneven light intensity of the Rod Lens array
3) Differences in transmission light intensity in the center and periphery of the lens
4) Differences in light intensity in the center and periphery of the LEDs
5) Deterioration of the LEDs
The machine performs shading correction to even out the original reading sensor output.
There are two types of shading correction: shading adjustment performed in the service mode
and shading correction performed for each job.
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