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IMAGE PROCESSING
3 December 2004
Scale processing
This process generates image densities of up to 256 levels for each pixel. It uses
simple binary, dithering, and error diffusion processing.
Simple binary processing sets the level based on a threshold value. There are no
shades of gray. The output is black or white only.
Dither processing is used to reproduce originals with continuous tones, such as
photographs on machines that cannot output true grayscales. It produces different
shades of gray by creating patterns of black and white dots. There are no gray
dots.
The error diffusion process 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 then compared with
a matrix table. Error diffusion is often used in text/photo mode. It is a good
compromise because it reduces the contrast between light and dark areas of
halftone images, while having no effect on letter areas.
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