Minolta CF910 Service Manual page 41

1 Photoelectric Conversion: PWB-A
• A reduction-type color CCD Sensor is used.
• The R, G, and B chips of the CCD Sensor read the light reflected off the original
and convert the optical data into a corresponding analog electric signal.
• To make data processing faster, data transfer and output are done through two
channels, one for even-numbered pixels and the other for odd-numbered pixels.
2 Analog-to-Digital Conversion: PWB-B
The odd and even analog signals output from the CCD Sensor chips are synthe-
sized to form a single string of signal data which is in turn converted to 8-bit digital
signals.
3 Shading Correction: PWB-C
An error is corrected that occurs due to variations in sensitivity of each CCD chip
and the light distribution varying along the length of Exposure Lamp LA1.
Operation:
1. Before the start of each copy cycle, light from LA1 strikes the shading sheet and
the CCD Sensor reads the light reflected off this sheet.
2. This reading is compared with the shading sheet reading reference value (white
reference value = max. value of image data) to determine the correction value
for each pixel.
3. When the image is scanned, each pixel data is corrected with the above correc-
tion value.
To prevent adverse effects on the image due to dust on the shading sheet, the max-
imum value of the readings taken in the sub-scanning direction of the shading sheet
is taken. This is called peak value hold.
4 Line-to-Line Variation Correction: PWB-C
• The R, G, and B chips of the CCD Sensor are placed so that there is a gap of 4
lines in the sub-scanning direction between the two adjacent chips (R → G → B).
This results in a deviation in the scanning position of the original. (The slower the
scanning speed, the greater the amount of deviation.)
• A memory called FIFO is used to compensate for this deviation. It retards the
output timing for R and G data to match it with that for B data.
R data
G data
B data
FIFO (first-in-first-out): Data is output in the same order as it is input.
FIFO
FIFO
M-24
FIFO Output
Output
Output