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e-STUDIO3511/4511 IMAGE PROCESSING 7 - 6 November 2003 © TOSHIBA TEC
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(c) Filtering
This function is enabled by low-pass filter processing and high-pass filter processing.
• Low-pass filter processing
This processing removes image/electrical noise and decreases moire by performing averaging
operation between the image signals of the targeted pixel and those of the neighboring pixels
to enhance the reproducibility of original.
<Example> Density of the targeted pixel position is X. Density of pixel positions at front and
back of the targeted pixel are “a” and “b” respectively. X is converted to X’ through
the low pass filtering.
When the matrix is (3 x 1):
The above averaging operation is performed for all the pixels to accomplish the high
reproducibility of original.
(The following is the case that the low pass filtering is applied on the primary scanning pixel.)
Fig. 7-302
• High-pass filter processing
Character outline blurs when the original, such as text, with big difference in density among the
pixels is optically scanned and output from the CCD. Characteristic of the lens and other factors
cause this phenomenon. In this equipment, processing such as edge enhancement is applied
between the targeted pixel and the neighboring pixels to eliminate this phenomenon and realize
high reproducibility of original.
Density
After low-pass filter
Primary scanning pixel positions
a + b + x
3
x’ =
Solid black area
Density
Primary scanning pixel positions
axb
Fig. 7-303
Original
Image signal
After correction
Low contrast area