Mmr Coding Scheme - Canon FACSIMILE BASIC 2000 Service Manual

G3 FACSIMILE COMMUNICATIONS
4.3.6 Effect of MR coding scheme
The table shows the size of compressed data by the MR coding scheme and
the MH coding scheme.
In the document example in Fig. 5-23, the compression ratio becomes
about 71% as shown in the following formula by the MR coding scheme
compared with the MH coding scheme.
Data size by MR coding / Data size by MH coding = 278/390 = 0.7128 ...
Approx. 71%
In actual coding of the document, the compression ratio becomes between
about 70% to 90% depending on the pattern of the document and the
cal scanning
4.4

MMR Coding Scheme

MMR stands for Modified Modified READ, and somewhat resembles the
MR coding scheme. By MMR, coding starts from a white line, and there
are no restrictions in parameter K. In other words, the initial line is taken to
the be the reference line, and only differences from the previous line are
coded by MR right until the end of the page. For this reason, as a condition
for use of MMR, MMR is limited to instances where error-free communi-
cations can be assured. So, with G3 facsimiles, MMR is used only in com-
binations with the ECM (Error Correction Mode) of
5–28
Table 5-7 Comparison of the Effect by MR Coding and MH Coding
MR coding
1st line
2nd line
3rd line
4th line
5th line
6th line
7th line
8th line
Total
line density.
43 bits
14 bits
56 bits
34 bits
55 bits
22 bits
24 bits
30 bits
278 bits
MH coding
41 bits
29 bits
56 bits
54 bits
54 bits
54 bits
48 bits
54 bits
390 bits
verti-
ITU-T described later.