Canon imageFORMULA DR-2580C, Service Manual

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COPYRIGHT © 2005 CANON ELECTRONICS INC. CANON DR-2580C FIRST EDITION APR. 2005
CHAPTER 2 FUNCTION & OPERATION
b) Error Diffusion
Error diffusion processing is used to
binarize documents containing gray
levels, such as pictures and photos.
A sample case is shown below, where
the output is set to four bits and the
slice level is set to “8.”
The value of 1 picture element of input
image data is compared with the slice
level. When it is smaller than the slice
level, it is output as “0” and when it is
bigger then the slice level, it is output
as “15.” The difference between the
values of the input and output picture
elements is then added to the next
picture element to be processed.
First, when processing the first low of
Line 1, since the data “12” is larger than
the slice level “8,” the output data be-
comes “15,” and the resultant error
becomes -3 (=12-15). (Figure 2-512)
12 9 6 3 1 9 13
Input data
15
Output data
12>8
→
"15"
-3
Error -3=(12-15)
Output
Input
First row of line 1
Figure 2-512
Next, when processing the second row
of Line 1, since the error is diffused to
the right, the data of the picture ele-
ment of the second row of Line 1 be-
comes “6” (=9-3).
As this value is smaller than the slice level, the output data is “0” and the
error becomes “+6” [=(9-3)-0]. (Figure
2-513)
The third row of Line 1 and later are
processed similarly.
12 9 6 3 1 9 13
Input data
15
(9-3)=6<8
→
"0"
+6
Error +6=(9-3)-0
Error of first row of Line 1
Input
Second row of line 1
0
Error of first row of Line 1
Output
Output data
Figure 2-513