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20 September 1999
• Edge detection: SP4-931 (vertical direction), 4-932 (horizontal direction), 4-933
(diagonal from top right to bottom left), 4-934 (diagonal from top left to bottom
right). Decreasing the SP mode value causes a lighter line to be detected as an
edge.
• Threshold limits for edges, and the threshold for non-edge pixels: SP4-924
(Max), 4-925 (Min), and 4-926 (Center, used for non-edge pixels). The closer that
the upper or lower limit is adjusted to the center threshold, the fewer stains
appear. However, a low ID contrast image cannot be copied.
Error Diffusion
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 compared with an
error diffusion matrix.
If the user selects "Service Mode" for Text (greyscale mode) or Text/Photo
(greyscale or binary picture mode) and the thresholding type is changed from
constant to dynamic, an error diffusion matrix can be selected with SP4-929-1
(No.1: 4 x 4 matrix and No.2: 8 x 8 matrix). The two selections are prepared for
future use to match original types which are not supported currently. Therefore, at
this moment SP4-929-1 should not be used.
Error diffusion cannot be selected in Photo mode.
Dithering
Each pixel is compared with the pixel in the same position in a dither matrix.
Several matrixes are available, to increase or decrease the detail on the copy. If
the user selects "Service Mode" for Photo original type, the dither matrix can be
selected with SP4-929-3 and SP4-929-5. A larger value for this SP mode increases
the number of gradations. However, the image will not have much contrast.
Line width correction
This function is effective only in pale mode and copied original mode (these are
original types for Text mode with greyscale).
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 is done in the IPU chip.
The line width correction type can be selected with SP4-935.
2-27
IMAGE PROCESSING
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