Canon fax basic 2000 サービスマニュアル
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G3 FACSIMILE COMMUNICATIONS
unwanted areas exist is called “redundancy”. The larger the redundancy,
the greater the effect of coding becomes.
Fig. 5-6 Examples of Documents with High Redundancy
Let’s consider the document shown in Fig. 5-7 below. When the focus is
applied to a certain scanline, it will be noted that the scanline comprises
white pixel groups and black pixel groups. The respective pixel groups are
referred to as the “white run” and “black run.” This characteristic is used
to allocate codes with high efficiency to these runs to reduce the size of the
image information. This is called “redundancy suppression coding” or
“redundancy compression coding”. From here on in this chapter, let’s sim-
ply refer to this as “coding.”
Fig. 5-7 Example of Document
Although various coding schemes are possible, the most efficient one is the
Huffman scheme. A slightly modified version of this scheme, the Modified
Huffman coding scheme (MH coding scheme), has been adopted as the
standard coding scheme for G3 facsimiles.
Example of document
containing characters
containing characters
Example of completely
black document
black document
White
run
run
Black
run
run
White
run
run
Black
run
run
White
run
run
Scanline is a group of
white runs and black runs.
white runs and black runs.
Scanline