Dell 3115CN, Service Manual

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Chapter 6 Principle of Operation (Scanner)
Version 1 2006.11.21
13. Control
13.1 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.
Compensation 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.
13.1.1 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 CCD Image Sensor
as the white reference value, which is used to adjust CCD Image Sensor output.
13.1.2 AOC (Auto Offset Control)
AOC is performed by turning off the Exposure Lamp after AGC. This state is read by the CCD Image
Sensor as the black reference value, which is used to adjust CCD Image Sensor output. (The order of
AGC and AOC adjustment depends on the model.)
13.1.3 Shading Compensation
Shading compensation compensates for pixel-by-pixel sensitivity variations and the nonuniformity 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.