Filtering, Main Scan Magnification/Reduction - Ricoh A230 Service Manual

IMAGE PROCESSING

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 moire 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
There are two software filters for enhancing the desired image qualities of the
selected original mode: the MTF filter and the smoothing filter.
The MTF filter emphasizes sharpness and is used in text and text/photo modes.
The smoothing filter is used in photo mode.
The relationships between the coefficient of the filter and the filter strengths are as
follows. The filter strengths and the coefficient for each mode can be adjusted with
SP4-903.
MTF Filter Coefficient (SP4-903-11~15, 17~19, 41~47)
(Weak) 11 → 8 → 2 → 1 → 9 → 0 → 5 → 4 → 10 → 7 → 3 → 6 (Strong)
MTF Filter Strength (SP4-903-20~27, 50~53, 55)
(Weak) x0.25 → x0.5 → x1 → x2 → x4 (Strong)
Smoothing Filter Coefficient (SP4-903-16)
(Weak) 7 → 6 → 0 → 5 → 2 → 1 → 3 → 4 (Strong)
A stronger MTF filter leads to sharper lines. A stronger smoothing filter leads to a
greater degree of smoothing.
Refer to the tables in 'SP Modes for Each Image Process' for more information.
Main scan magnification/reduction
Reduction and enlargement in the sub scan direction are done by changing the
scanner speed. However, reduction and enlargement in the main scan direction
are handled by the IPU chip.
To reduce or enlarge an image, imaginary points are calculated that would
correspond to a physical enlargement or reduction of the image. The image density
is then calculated for each of the imaginary points based on the image data of the
nearest four true points. The calculated image data then becomes the new
(reduced or enlarged) image data.
A230/A231/A232
2-14
SM