Chapter 10 Principle of Operation
10.12 Control
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10.12 Control
10.12.1 Document Scanning Steps
A CCD Image Sensor is used to read image data from the document. To ensure stabilized image reading, the
CCD Image Sensor output is adjusted. Adjustment includes Automatic Gain Control (AGC) and Automatic
Offset Control (AOC).
Reference data for adjustment is collected and used to perform compensation on the read image data. Com-
pensation includes shading compensation, white variation compensation, and black variation compensation.
These adjustment and compensation steps are described below.
Reference data is obtained by reading image data from a white reference plate via the CCD image sensor.
AGC (Auto Gain Control): White Level Variation Adjustment
During AGC, the Scanner ASSY is moved to the position of the white reference plate, and the Exposure
Lamp is illuminated. The light reflected from the white reference plate is read by the CMOS Image Sen-
sor as the white reference value, which is used to adjust CMOS Image Sensor output.
AOC (Auto Offset Control)
AOC is performed by turning off the Exposure Lamp after AGC. This state is read by the CMOS Image
Sensor as the black reference value, which is used to adjust CMOS Image Sensor output. (The order of
AGC and AOC adjustment depends on the model.)
Shading Compensation
Shading compensation compensates for pixel-by-pixel sensitivity variations and the non uniformity of
lamp light in the fast scanning direction. The AGC and AOC adjustment values are used to compensate
for the image data read by the CCD Image Sensor.
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