Ricoh K-C3 Service Manual page 226

B245/B276/B277/B268/B269 Service Manual
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 8-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,
Photo 2, Special 2, and Special 5 by default, but can also be applied to Photo 1 and 3 by
changing the value of SP 4926.
Texture removal uses 256 threshold values in an 8 x 8 matrix. The value of SP 4926 controls
the application of Texture Removal for each of the 6 modes listed above. The settings are as
follows:
0: The default value for each mode is used. Text 1, Photo 2, Special 2, and Special 5 have a
default of 3 (see below) and Photo 1 and 3 have a default of 1.
1: No removal applied.
2 – 6: 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.
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