Ccd Output Gain Correction, Offset Correction; Ccd Output A/D Conversion; Outline Of Shading Correction; Shading Adjustment - Canon imageRUNNER 7095 Service Manual

5.3.6.5 CCD Output Gain Correction, Offset Correction

The machine processes the analog video signals from the CCD so that the rate of their amplitude is a spe-
cific level. The machine also makes sure that the output voltage in the absence of incident light is of a spe-
cific level (offset correction).

5.3.6.6 CCD Output A/D Conversion

The odd-numbered and even-numbered pixel analog video signals after correction are further converted
into 12-bit digital signals representing specific pixel voltage levels by the A/D converter.

5.3.6.7 Outline of Shading Correction

The machine executes shading correction so that the CCD output will be even when the density of the orig-
inal is even.
The output of the CCD may not necessarily be even because of the following factors even if the density of
the original is perfectly even:
1. variation in the sensitivity of the individual pixels of the CCD
2. difference in the degree of light passing through the center of the lens and through its edge
3. difference in the intensity of light between the center and ends of the scanning lamp
4. deterioration of the scanning lamp
The machine executes shading correction to make up for the variation in the output of the CCD.
Shading correction may be shading adjustment executed to determine a service mode target value or shad-
ing correction executed for every job.

5.3.6.8 Shading Adjustment

In shading adjustment, the machine measures the density of a white sheet of paper and the standard white
plate, and stores the measurements in memory. The machine then computes these measurements for use
as the target value for shading correction. Shading adjustment is executed at time of machine installation
or scanning lamp replacement, or when a change has occurred in the intensity of light over time.
Service Mode:
COPIER>FUNCTION>CCD>CCD-ADJ

5.3.6.9 Shading Correction

The machine executes shading correction for every scan of an original.
The machine shines the light of the scanning lamp against the standard white plate, and measures the light
reflected by the plate; it then uses the analog image processing block of the CCD/AP PCB to turn the meas-
urements into digital data, which will be sent to the shading correction circuit of the reader controller PCB
in the form of a shading coefficient.
In the shading correction circuit, the shading coefficient is compared against the target value stored in
memory, and the machine uses the differences as the shading correction value.
The shading correction value is used to make up for the variation among individual pixels of the CCD oc-
curring at each scan, thus evening out the image density level.
CCD output
Target value
Measurement
Characteristics after
Characteristics before
White
Standard white plate
F-5-51
correction
correction
Original density
Chapter 5
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