Lexmark X940E, Service Manual

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General information
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The CCD image sensor is used to read image data from the document. To stabilize the read image data, the
CCD image sensor output is adjusted and the read image data is compensated.
The CCD image sensor output is adjusted with the gain/offset voltage of the amplifier in the analog circuit. This
adjustment includes AGC and AOC.
In addition, the reference data is collected and compensation values are calculated to compensate for the read
image data. This compensation includes shading compensation, white variation compensation, and black
variation compensation. These adjustment and compensation steps are detailed below.
The reference data is prepared by reading the image data of a white reference plate via the CCD image sensor.
AGC (auto gain control): white level coarse adjustment
AGC is a function that adjusts the gain so that the CCD image sensor output becomes as specified when the
exposure lamp is on. AGC functions as a coarse white level adjustment of the image. AGC is performed at
initialization.
AOC (auto offset control)
AOC is a function that adjusts the offset voltage so that the CCD image sensor output becomes as specified
when the exposure lamp is off. AOC functions as a black level adjustment of the image. AOC is performed at
initialization.
Shading compensation
Shading compensation is a function that compensates for pixel-to-pixel sensitivity variation of the CCD image
sensor and pixel-to-pixel output variation of the CCD image sensor that is caused by illumination non uniformity
in the fast scanning direction of the optical system.
Shading compensation is performed at initialization.
White level variation compensation
White level variation compensation is performed to compensate for variation in light quantity of the exposure
lamp.
White level variation compensation includes two processes: acquisition of white variation compensation
reference data during initialization and white variation compensation during document scanning.
For the ADF, white level variation compensation is performed at both the white reference plate position of the
platen and at the white reference plate of the scanner read position.
Black level variation compensation
Black level variation compensation is performed to compensate for variation in black level that is caused by the
temperature drift of the CCD image sensor and analog circuit.
Black level variation compensation is performed during document scanning.
For the platen, black level variation compensation is performed at the white reference plate position of the
platen. For the ADF, black level variation compensation is performed at the scanner read position.