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(2) Vertical mode
When this mode is detected, the position of a1 is coded at a position rela-
tive to the position of b1. The relative distance a1b1 can take on one of
seven values V(0), VR(1), VR(2), VR(3), VL(1), VL(2) and VL(3), each
of which is expressed by a separate code word. The subscripts R and L
indicate that a1 is to the right or left respectively of b1, and the number in
brackets indicates the value of the distance a1b1. After coding in the verti-
cal mode has been performed, the position of a0 is moved to a1 (See Fig.
5-21).
(3) Horizontal mode
When this mode is detected, both the run lengths a0a1 and a1a2 are coded
using the code words "H + M(a0a1) + M(a1a2)". H is the flag code word
"001" taken from the MR code table (Table 5-5). M(a0a1) and M(a1a2) are
code words which represent the "length" and "color" of the runs a0a1 and
a1a2 respectively, and are coded from the appropriate white or black MH
code tables (Tables 5-2 and 5-3). After a coding in the horizontal mode is
performed, the position of a0 is moved to a2 (see Fig. 5-21).
Reference line
Coding line
Fig. 5-21 Vertical Mode and Horizontal Mode
G3 FACSIMILE COMMUNICATIONS
Vertical mode
a1 b1
a0
a1
a0 a1
Horizontal mode
b1
b2
a2
a1 a2
5–23
1
2
3
4
5
6
ït
çi
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