Shading Adjustment; Shading Correction - Canon imagerunner C5180 Service Manual

Chapter 6
The machine executes either of the following 2 shading mechanisms: shading correction it carries out for every
copy and shading adjustment for which the target value is set in service mode.

6.3.6.6 Shading Adjustment

The machine performs shading adjustment in response to a command made in service mode. The machine
measures the density of blank white paper and that of the white plate to obtain density data; it then computes the
data to produce the target value for use at time of shading correction.

6.3.6.7 Shading Correction

The machine executes shading correction each time it scans an original.
The machine directs the light from the scanning lamp against the standard white plate, and converts the reflected
light into a digital signal by the analog image processing block on the CCD/AP PCB. The result (i.e., a digital
signal representing the intensity of the reflected light) is sent to the shading correction circuit of the reader
controller PCB as a shading coefficient. The shading correction circuit in turn compares the coefficient against
the target value it holds, and offers the difference as the shading correction value.
The machine uses the shading correction value to correct the variation that may exist among the individual
pixels of the CCD, thereby keeping the image density to a specific level at all times.
CCD output
Characteristics after
correction
Target value Characteristics before
correction
Measurement
White
Original density
Standard white plate
F-6-35
6-23