Random Error Diffusion; Ed) Method - Canon ImageRunner 600 Service Manual

CHAPTER 4 IMAGE PROCESSING SYSTEM
2. Random Error Diffusion (R-ED) Method
In the existing error diffusion (ED) method, a fixed pattern (error diffusion matrix) is used to
diffuse (distribute) errors occurring as a result of binary processing over surrounding pixels, possi-
bly generating specific patterns on the output images. To reduce such patterns, the copier adds
random values to the image signals representing pixels (hence, random error diffusion).
Step 1
A random number is added to the image signal
representing each pixel.
Step 2
×0.05
×0.01 ×0.1
×0.05
×0.1
Figure 4-305B Conceptual Diagram of the Error Diffusion Method
4-16
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+
-
+
-
×0.2
×0.2
×0.1 ×0.1
×0.03
×0.05
×0.01
At this time, a value that brings the sum to
0 is added to the adjacent pixel to prevent
an error caused by the random number.
Error Diffusion Matrix (fixed pattern)
Each error is diffused (distributed)
to the surrounding pixels according to the
ratio of the error diffusion matrix.
Pixel in question (e.g., density at 135)
When the slice level used for binary
processing is 128, this pixel will be a black
pixel (255).
In this case, the diffusion will be 125 (255 -
135).
Black(255)
Slice level
(128)
White(0)
CANON imageRUNNER 600 REV.1 JAN. 2000 PRINTED IN U.S.A.
Error
Pixel in question
(density at 135)