Control; Document Scanning Steps; Aoc (Auto Offset Control); Agc (Auto Gain Control): White Level Variation Adjustment - Dell 2135cn Service Manual

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13. Control

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

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.)

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.

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.

Version 2 2008.03.31

Chapter 6 Principle of Operation (Fax)

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