Canon imagePRESS C1, Руководство по обслуживанию

Страница: 294 / 1265

Chapter 5
5-15
5.3.6.3 CCD Gain Correction, Offset Correction
0012-9686
imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+
The analog video signal from the CCD is processed so that the rate of amplification is even (gain correction); the output in the absence of incident light is also
processed for a specific level (offset correction).
5.3.6.4 CCD Output A/D Conversion
0012-9691
imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+
The odd-numbered and even-numbered pixel analog video signals after the foregoing correction are then converted into 10-bit digital signals by the A/D converter
according to their pixel voltage levels.
5.3.6.5 Outline of Shading Correction
0012-9692
imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+
The output of the CCD may not always be uniform because of the following reasons even when the density of the original in question is uniform:
- variation in the sensitivity among individual pixels of the CCD.
- difference in the level of transmission between the center and the edge of the lens.
- difference in the intensity of light between the middle and the edges of the scanning lamp.
- deterioration of the scanning lamp
The machine executes shading correction to even out the output of the CCD.
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.
5.3.6.6 Shading Adjustment
0012-9693
imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+
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.
5.3.6.7 Shading Correction
0012-9694
imagePRESS C1 / Color Image Reader-H1 / imagePRESS C1+ (Printer) / imagePRESS C1+
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.
F-5-35
CCD output
Original density
Standard white plate
Characteristics before
correction Target value
Measurement
Characteristics after
correction
White