Ricoh A250 Service Manual page 77

• 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.
When used with error diffusion (Normal Text)
After error diffusion processing, dynamic thresholding uses 64 threshold values in
an 8 x 8 matrix. This process prevents low contrast text from disappearing.
If the user selects "Service Mode" for Text/Photo original type and the thresholding
type is changed from constant to dynamic, an error diffusion filter 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.
Dithering
If the user selects "Service Mode" for Text/Photo original type, the dither matrix can
be selected with SP4-929-2. A larger value for this SP mode increases the number
of gradations. However, the image will not have much contrast.
SM 2-19
IMAGE PROCESSING
A250