Ricoh LD013, Service Manual

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IMAGE PROCESSING
SM 6-27 B039/B040/B043
Gradation Processing
Overview
There are three types of gradation processing (listed below). Refer to the “Default
Image Processing Mode for Each Original Type” section for more details on which
processes are used for each original mode.
•
Binary picture processing
•
Error diffusion
•
Dithering
Binary Picture Processing
The 6-bit image data is converted into 1-bit data (black and white image data). This
is done when the user selects Text 2 or Special 1. The threshold for deciding
whether a pixel is black or white cannot be adjusted.
Error Diffusion
Error diffusion reduces the difference in contrast between light and dark areas of a
halftone image. Each pixel is corrected using the difference between it and the
surrounding pixels. The corrected pixels are compared with an error diffusion
matrix.
Error diffusion is applied when the user selects Text 1, Photo 1-3 and Special 2
and 5.
As the final step in error diffusion, a process called Texture Removal is applied to
Text 1, Special 2, and Special 5 by default, but can also be applied to Photo 1-3 by
changing the value of SP4-926.
Texture removal uses 64 threshold values in an 8 x 8 matrix. The value of SP4-926
controls the application of Texture Removal for each of the 5 modes listed above.
The settings are as follows:
0: The default value for each mode is used. Text 1, Special 2, and Special 5 have a
default of 3 (see below) and Photo 1-3 have a default of 1.
1: No removal applied.
2 – 5: Removal applied at the level specified here. The higher the setting (level),
the less clear the image will become (more texture removal).
Dithering
Each pixel is compared with the threshold in a dither matrix. Several matrices are
available to bring out half-tone areas in images such as newspaper-type
photographs. Dithering is only used for Special 3 and Special 4.