IMAGE PROCESSING
2-36
A229 SM
2.3.10 FILTERING, MAIN SCAN MAGNIFICATION/REDUCTION
Overview
After auto shading, the image data is processed by both filtering and main scan
magnification. However, to reduce the occurrence of moiré in the image, the
processing order depends on the reproduction ratio, as follows.
1. 64% reduction or less
Main Scan Reduction
→
Filtering
2. 65% reduction or higher
Filtering
→
Main Scan Magnification
Filtering
By default, an individual MTF filter is used for each image processing mode, to
enhance the desired image qualities. (For photo mode, smoothing filter is selected
as the default setting.)
A stronger MTF filter emphasizes sharpness and leads to better reproduction of
low image density areas, but may lead to the occurrence of moiré in the image.
When adjusting a filter, adjust the coefficient first. If that does not satisfy the user,
then adjust the strength (it may be necessary to do some fine tuning with the
coefficient after adjusting the strength).
For text mode, the filter coefficient and strength can be adjusted in the main scan
and sub scan directions individually. This allows the copy quality to be adjusted
more precisely, to match the originals normally scanned by a particular customer.
Example:
In a case when vertical lines (sub scan) are reproduced clearly, but
horizontal lines (main scan) are not reproduced clearly, the technician can adjust
the main scan filter only.
For photo mode, the smoothing filter is the default filter, but the MTF filter may be
selected by SP mode. This is effective when putting more weight on improving the
resolution when copying from “continuous tone” originals.
For text/photo mode, a different MTF filter is applied for the text and photo areas
that were determined during text/photo separation. The filter type for each area
may be changed with SP mode. This is done in SP4903-017 for text areas, and
SP4903-047 for photo areas.
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