22 December 1998
IMAGE PROCESSING
2-17
Detailed
Descriptions
2.4.2 SBU
The CCD converts the light reflected from the document into an analog signal. The
CCD line has 5,000 pixels and the resolution is 400 dpi (15.7 lines/mm).
The CCD has two output lines, for odd and even pixels. Each of these has an
analog processing IC. The analog processing IC performs the following operations
on the signal from the CCD.
1. Z/C
(Zero
Clamp)
Adjusts the black level reference for even pixels to mach the odd pixels.
2. Signal
Amplification
Operational amplifiers in the AGC (Auto Gain Control) circuit amplify the analog
signal. The CPU on the SCU board controls the maximum gains of the
operational amplifiers.
After the above processes, the analog signals are converted to 8-bit digital signals
by the A/D converters. This gives a value for each pixel on a scale of 256 grades.
Then these signals go to the SCU board.
CCD
S B U
A/D 1
A/D 2
O
E
S C U
IOB
8 bit data
8 bit data
Analog
Processing IC1
Analog
Processing IC2
I P U
G411D507.WMF
