Ricoh PRIPORT VT 2000 Series Service Manual page 51

28 February '91
The reference (VR+) of the D/A converter is set to the peak hold of the
original background. Distortion correction is obtained by using the output
voltage of the D/A converter as the reference voltage (V ) of the A/D
H
converter; therefore, distortion correction also corrects for the original
background level.
For Example: If the light intensity at a certain pixel is very high, then a high
voltage level will be stored in the distortion memory location for that pixel.
When reading a document, that high voltage level is used as the reference
level (V ) of the A/D converter. Therefore, during conversion, the input level
H
from the pixel is compared to a high voltage by the A/D. This negates any
errors caused by the high light intensity at that pixel.
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