Ricoh PRIPORT VT 2000 Series Service Manual page 60

VT2300/VT2500 Circuit in Photo Mode:
VPH of Shading Distortion
Memory
VPH of Platlen/
Original
Background
CN601-24
Density : 0
CN601-25
Density : 1
The printing density (i.e. image density) can be changed with the Printing
Density key on the operation panel. This adjustment can also be done in
Photo mode to increase the image quality of photo originals.
Photo ode Selector changes the threshold level of VH (White level
reference) and VL (Black level reference) according to the density signals
from CN 601-24 and CN 601-25.
The A/D converter converts the analog input signal to a 4-bit digital signal
using both the white reference level (VH) and the black reference level (VL).
The following table shows the VH and VL levels that vary according to the
combination of the density signals in Photo mode.
Density
Printing Signal 0
Density (CN601-
24)
Darker 2 H
Darker 1 L
Standard H
Lighter L
Photo Mode
Selector
3
95%
2
X
80%
1
80%
0
70%
3
10%
2
Y
10%
1
4%
0
4%
A B
PHTO
(Low signal when in Photo mode)
Density
Signal 1 Photo Mode Selector
(CN601- ON Channel.
25)
H
H
L
L
2-33
Selector 2
2
X
Y
2
A
B
SHMRT (Low signal when in Photo/Line mode)
0X, 0Y
1X, 1Y
2X, 2Y
3X, 3Y
28 February '91
VH
M1
M2
VL
A/D Converter
A/D Converter
VH VL
95% 10%
80% 10%
80% 4%
70% 4%
4 bit
Image
Signal