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AR-651/810 IMAGE PROCESSING 7 - 5
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(b) Filtering
This function is enabled by a low-pass filter circuit and a high-pass filter circuit.
•
Low-pass filter circuit
This circuit removes image noise and electrical noise, decreases moire, and realizes high
reproducibility of original by applying an averaging operation on the image signal of the targeted
pixel and those of the pixels positioning next to it.
<Example> The density of the targeted pixel position is “x”. The density of the pixel positions at
the front and back of the targeted pixel are “a” and “b” respectively, “x” is converted to
“ x’ ” through low pass filtering.
When the matrix is (3 x 1):
The above averaging operation is performed for all the pixel positions to accomplish the high
reproducibility of the original.
The following is when low pass filtering is applied on the primary scanning pixel.
•
High-pass filter circuit
The change of the density at the character outline becomes smooth when an original, such as text,
with a great difference in density between the pixels placed next to one another is optically scanned
and output from the CCD. This is caused by the characteristic of the lens and other factors. In this
copier, the process such as the edge enhancement, is applied on the targeted pixel and the pixels
around it to eliminate this phenomenon and realize high reproducibility of the original.
Density
After low-pass filtering
Primary scanning pixel positions
a + b + x
3
x’ =
Original
Image signal
After correction
Low contrast area
Solid black area
Density
Primary scanning pixel positions
a
x
b
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