Filtering; Pre-Filter - Gestetner B003 Service Manual

Filtering

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
There are two software filters: MTF and smoothing.
MTF emphasizes lines parallel to the direction of feed. There are four types of MTF
setting:
• Filter coefficient for main scan direction
• Filter strength for main scan direction
• Filter coefficient for sub scan direction
• Filter strength for sub scan direction
Refer to the following charts to determine how to make the filters weaker or
stronger. The values in bold are the default settings.

Pre-Filter

Pre-Filter smoothes mainly parallel lines in the main scanning direction and
extended lines in the sub-scanning direction. The Pre-Filter is a setting intended for
use with the Text/Photo modes and cannot be used with the initial settings of other
modes. Setting a large value for the Pre-Filter setting greatly increases the
smoothing of parallel lines and reduces moiré and spurious "noise" in images, but
may also reduce sharpness and lower contrast.
(Weak) 0 (Off) → 1 → 2 → 3 (Strong)
• SP-903-10: Text Mode (25%~64%)
• SP-903-11: Text Mode (65%~154%)
• SP-903-12: Photo Mode
• SP-903-13: Text/Photo Mode (25%~64%)
• SP-903-14: Text/Photo Mode (65%~154%)
• SP-903-15: Low Density Mode
• SP-903-16: Generation Mode (25%~64%)
SM 6-29
IMAGE PROCESSING
B003/B004/B006/B007