Ricoh PRIPORT VT 2000 Series Service Manual page 52

2.5.4 Original Background Correction
White Peak Hold of Platen Cover
53%
VT2100/2130/2150: 1.7V
VT2300/2500: 1.4V
As the white peak hold of the original background is used as the reference
(VR+) of the D/A converter, the overall shading distortion correction level is
adjusted for the original background at the output of the D/A converter.
For Example, if the background level of the original is low, the reference
level (V ) of the D/A converter is low, causing the overall distortion
H
correction level to be low. Therefore, even though the light level from the
original background is low, it is being compared to a low reference level
(V ) which causes it to be detected as background, not image.
H
VPH
<Original background is lighter.>
Peak Hold of Original Background
VPH
53%
VT2100/2130/2150: 1.7V
VT2300/2500: 1.4V
<Original background is darker.>
Peak Hold of Original Background
VPH
53%
VT2100/2130/2150: 1.7V
VT2300/2500: 1.4V
2-25
28 February '91