Filtering - Ricoh Aficio 220 Service Manual

20 September 1999 IMAGE PROCESSING

Filtering

Overview
There are some software filters for enhancing the desired image qualities of the
selected original mode. These filters are the MTF filter, the smoothing filter, and
independent dot erase.
The MTF filter emphasizes sharpness and is used in Text and Text/Photo modes.
The smoothing filter is used in Photo mode, except for Glossy Photo mode. In
Glossy Photo mode, the MTF filter is used.
Independent dot erase removes unwanted dots from the image.
MTF Filter Adjustment - Text and Text/Photo Modes
When the user selects "Service Mode" for either Text or Text/Photo original type,
the MTF filter strength and coefficient can be adjusted with SP4-915 and 4-916.
It is difficult to simply explain the relationships between the filter coefficient and
filter strengths. Refer to the following charts to determine how to make the filters
weaker or stronger. A circle indicates the default setting.
When the filter is stronger in the main scan direction, lines parallel to the feed
direction are emphasized. When the filter is stronger in the sub-scan direction, lines
at right angles to the feed direction are emphasized. A stronger MTF filter can
make a low ID image visible but moiré may become more visible. Moiré is reduced
using a smoothing filter specially designed for this purpose (see "Smoothing Filter
Adjustment - Text/Photo").
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