Xerox Phaser 6180MFP, Service Manual

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2-88 Phaser 6180MFP Multifunction Printer Service Manual
Theory of Operation
Control
Document Scanning Steps
A CCD Image Sensor is used to read image data from the media. The CCD
Image Sensor output is adjusted to ensure the image reading is stabilized.
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, white variation, and
black variation compensations. These adjustment and compensation steps
are described below:
1. AGC (Auto Gain Control): White Level Variation Adjustment
During AGC, the Scanner Assembly 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 the CCD Image Sensor
output.
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 the CCD Image Sensor output. (The order of AGC
and AOC adjustment depends on the model.)
3. 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.