Toshiba 4580, Руководство по обслуживанию

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Mar. 1999 © TOSHIBA TEC 6 - 5 6570/5570 IMAGE PROCESSING
(B) Filtering
This function is comprised of a low-pass filter circuit and a high-pass filter circuit.
(a) Low-pass filter circuit
This circuit eliminates image and electrical noise as well as restrict Moire. It provides an image
that closely resembles the original document’s. It does this by averaging the differences between
the targeted pixel and those adjacent to it.
For example, assuming the density of the target pixel position to be x and the densities of its front
and back positions to be a and b, respectively, the density of the target pixel position x’ after low-
pass filter operation is given:
For (3 x 1) matrix,
The above operation is performed for all pixel positions to accomplish high original reproducibil-
ity.
The following figure shows the primary scanning pixel is processed by the low-pass filter.
(b) High-pass filter circuit
When images with sharp edges are scanned and directed to the CCD, the edges of these char-
acters tend to become dull in appearance. This is due to the physical imperfections of the CCD
lens as well as the mirrors that direct the light to it.
To compensate for this phenomenon, an edge-enhancement operation is performed. It recog-
nizes the differences in density between the targeted pixel and those adjacent to it an makes
compensations to ensure that the final output image closely resembles the image of the original
document. (See illustration below)
Density
After low-pass filter
operation
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
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9