1 August 1996IMAGE PROCESSING
3. Error Diffusion
This is used only in Text/Photo mode.
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 error diffusion matrix. Separate error diffusion matrixes
are used for copy mode and fax mode.
1) Grayscale processing mode
The output image signal level has 9 levels (from white to black).
There is only one matrix available.
2) Binary picture processing mode
The output image signal level has just 2 levels (white and black).
The threshold level can be changed with SP4-418-2.
4. Dithering
This is only used in Photo mode.
Each pixel is compared with a pixel in a dither matrix. Several matrixes are
available, to increase or decrease the detail on the copy.
1) Grayscale processing mode
The matrix type can be selected with SP4-421-1 and with UP mode.
2) Binary picture processing
The matrix type can be selected with SP4-421-2 and with UP mode.
2.4.7 Line Width Correction
This function is effective only in Letter mode.
Usually, lines will bulge in the main scan direction as a result of the
negative/positive development system that is used in this model. So, pixels
on edges between black and white areas are compared with adjacent pixels,
and if the pixel is on a line, the line thickness will be reduced.
The line width correction in grayscale processing mode is done in the IPU,
and in binary processing mode, it is done in the FCI chip.
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ACEC
