Line Width Correction - Gestetner A193 Service Manual

3. Error Diffusion
Error Difusion 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 using the service program mode, 418-2.
4. Dithering
Dithering 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 using the service program mode, 421-1
or the user tool program mode.
2) Binary picture processing
The matrix type can be selected using the service program mode, 421-2
or the user tool program 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 machine. So, the
pixels on the edges between black and white areas are compared with their
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.
SM 2-15
IMAGE PROCESSING
(A193)