Canon fax basic 2000 サービスマニュアル

G3 FACSIMILE COMMUNICATIONS

5–12

(2) MH coding

After being converted to run lengths, the scanlines are converted to MH

codes. These MH codes comprise terminating codes and make-up codes.

(See the table of page 5-14.) Different mechanisms are used for converting

to MH codes for when the run length is 0 to 63, and when the run length is

64 or more.

• Coding when the run length is 0 to 63

In this case, coding is performed with a suitable terminating code depend-

ing on the color and length of the run.

Fig. 5-11   MH Coding When The Run Length is 0 to 63

• Coding when the run length is 64 or more

In this case, coding is performed by a make-up code which shows the larg-

est run length without exceeding the run length of that run. Next, the dif-

ference between the actual run length and the length of the make-up code

is coded by a terminating code.

Fig. 5-12   MH Coding When The Run Length is 64 or More

White run length

5

Scanline after
conversion to
run length

MH codes
(terminating
codes only)

Black run length

3

White run length

9

Black run length

3

White run length

1708

1100

10

10100

10

Scanlines after
conversion to
run length

White run length

1708

00101101

011000

Make-up code

Terminating code

White run

length 44

White run

length 1664

MH code (make-up code + terminating code)