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DETAILED SECTION DESCRIPTIONS
October 9th, 1995
VIDEO DATA PATH
1. CCD
The CCD converts the light reflected from the original into an analog signal.
The CCD contains a row of 5,000 pixels at a resolution of 400 dpi (15.7
lines/mm).
The CCD has two output lines, for odd and even pixels.
2. Sample Hold
The sample hold circuit removes noise which is generated when the CCD
converts light to an analog signal.
3. Multiplexer
This merges the odd and even pixel analog signals from the CCD.
4. Gain Control
The output from the multiplexer is amplified. The gain range of the amplifier is
controlled by the CPU on the SCU board by monitoring the feedback signals
from the shading correction circuit.
5. A/D Conversion
The amplified analog signals are converted to 8-bit digital signals. This gives
256 gradations for each pixel.
6. Shading Correction
The machine scans the white plate opposite the ADF exposure glass to make
a white waveform. Shading correction prevents uneven images caused by
fluctuations in scanned data due to changes in light intensity and CCD
sensitivity.
7. Gamma Correction
The gamma curve corrects the response of the CCD to grayscales on the
original.
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