.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\"                 Not Copyright ( c) 1991 
.\"
.\" Assumes tbl, eqn, MS macros, and lots of luck.
.TA 1c 2c 3c 4c 5c 6c 7c 8c
.ds CH
.ds CF
.EQ
delim @@
.EN
.nr LL 40.5P
.nr ll 40.5P
.nr HM 3P
.nr FM 6P
.nr PO 4P
.nr PD 9p
.po 4P

.rs
\v | 5i'
.sp 2P
.LP
\fBRecommendation\ T.6\fR 
.RT
.sp 2P
.ce 1000
\fBFACSIMILE\ CODING\ SCHEMES\ AND\ CODING\ CONTROL\ FUNCTIONS\fR 
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.6''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.6	%'
.ce 0
.sp 1P
.ce 1000
\fBFOR\ GROUP\ 4\ FACSIMILE\ APPARATUS\fR 
.ce 0
.sp 1P
.ce 1000
\fI(Malaga\(hyTorremolinos, 1984; amended at Melbourne, 1988)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR 	\fBGeneral\fR 
.sp 1P
.RT
.sp 2P
.LP
1.1
	\fIScope\fR 
.sp 1P
.RT
.PP
1.1.1
Recommendation T.6 defines the facsimile coding schemes
and their control functions to be used in the Group\ 4 facsimile.
.sp 9p
.RT
.PP
1.1.2
This Recommendation should be read in conjunction with the
following Recommendations:
.sp 9p
.RT
.LP
	T.503
	A document application profile for the interchange of
Group\ 4 facsimile documents
.LP
	T.521
	Communication application profile for document bulk
transfer based on the session service (according to the rules defined in
T.62 | fIbis\fR )
.LP
	T.563
	Terminal characteristics for Group 4 facsimile
apparatus
.LP
	T.73 
	Document interchange protocol for the Telematic
services
.LP
	T.62 
	Control procedures for Teletex and Group 4 facsimile
services
.LP
	T.62 | fIbis\fR 	Control procedures for Teletex and Group 4
facsimile services based on Recommendations\ X.215/X.225
.LP
	T.70 
	Network\(hyindependent basic transport service for
Telematic services
.LP
	F.161
	International Group 4 facsimile service
.PP
In addition, in the case of Group\ 4 Class\ II/III (Teletex or mixed mode 
of operation), the following Recommendations should also be read: 
.LP
	T.60 
	Terminal equipment for use in the Teletex service
.LP
	T.61 
	Character repertoire and coded character sets for the
international Teletex service
.LP
	T.72 
	Terminal capabilities for mixed mode of
operation
.sp 2P
.LP
1.2
	\fIFundamental principles\fR 
.sp 1P
.RT
.sp 1P
.LP
1.2.1
	\fIFacsimile coding schemes and coding control functions\fR 
.sp 9p
.RT
.PP
Facsimile coding schemes
consist of the 
basic facsimile coding scheme
and optional facsimile coding schemes. They are defined in
\(sc\ 2 and \(sc\(sc\ 3 and\ 4, respectively.
.PP
Facsimile coding schemes are specified assuming that transmission
errors are corrected by control procedures at a lower level.
.PP
The basic facsimile coding scheme is the two\(hydimensional coding scheme 
which is in principle the same as the two\(hydimensional coding scheme 
of Group\ 3 facsimile specified in Recommendation\ T.4. 
.PP
Optional facsimile coding schemes are specified not only for black
and white images but also for grey scale images and colour images.
.PP
Facsimile coding control functions are used in facsimile user
information in order to change facsimile parameters or to invoke the end of
facsimile block. They are defined in \(sc\ 2.4.
.RT
.sp 2P
.LP
\fB2\fR 	\fBFacsimile coding schemes and coding control functions for\fR 
\fBblack and white images\fR 
.sp 1P
.RT
.sp 1P
.LP
2.1
	\fIGeneral\fR 
.sp 9p
.RT
.PP
This section specifies the facsimile coding schemes, and
associated control functions for black and white images.
.bp
.PP
Facsimile coding schemes consist of the basic facsimile coding
scheme and optional coding schemes.
.PP
The use of the optional facsimile coding schemes is subject to
mutual agreement between terminals and shall be initiated by the appropriate
procedural steps.
.RT
.sp 2P
.LP
2.2
	\fIBasic facsimile coding scheme\fR 
.sp 1P
.RT
.sp 1P
.LP
2.2.1
	\fIPrinciple of the coding scheme\fR 
.sp 9p
.RT
.PP
The coding scheme uses a 
two\(hydimensional line\(hyby\(hyline
coding
method in which the position of each 
changing picture
element
on the current coding line is coded with respect to the position of a corresponding 
reference element
situated on either the 
coding
line
or the 
reference line
which is immediately above the coding
line. After the coding line has been coded, it becomes the reference line 
for the next coding line. The reference line for the first coding line 
in a page is an imaginary white line. 
.RT
.sp 1P
.LP
2.2.2
	\fIDefinition of\fR 
\fIchanging picture elements\fR  |
(see Figure 1/T.6)
.sp 9p
.RT
.PP
A changing element is definied as an element whose \*Qcolour\*U (i.e. black 
or white) is different from that of the previous element along the same 
scan line. 
.RT
.LP
.rs
.sp 19P
.ad r
\fBFigure 1/T.6, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2.3
	\fICoding modes\fR 
.sp 9p
.RT
.PP
One of the three coding modes are chosen according to the coding
procedure described in \(sc\ 2.2.4 to code the position of each changing
element along the coding line. Examples of the three coding modes are given 
in Figure\ 2/T.6, 3/T.6 and\ 4/T.6. 
.RT
.sp 1P
.LP
2.2.3.1
	\fIPass mode\fR 
.sp 9p
.RT
.PP
This mode is identified when the position of b\d2\ulies to the
left of a\d1\u. (See Figure\ 2/T.6.)
.PP
However, the state where b\d2\uoccurs just above a\d1\u, as shown
in Figure 3/T.6 is not considered as a pass mode.
.bp
.RT
.LP
.rs
.sp 8P
.ad r
\fBFigure 2/T.6, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 9P
.ad r
\fBFigure 3/T.6, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2.3.2
	\fIVertical mode\fR 
.sp 9p
.RT
.PP
When this mode is identified, the position of a\d1\uis coded
relative to the position of b\d1\u. The relative distance a\d1\ub\d1\ucan take
on one of seven values V(0), V\dR\u(1), V\dR\u(2), V\dR\u(3), V\dL\u(1), 
V\dL\u(2) and V\dL\u(3), each of which is represented by a separate 
code word
. The subscripts\ R and\ L indicate that a\d1\uis to the right or left 
respectively of b\d1\u, and the number in brackets indicates the value 
of the distance 
a\d1\ub\d1\u(see Figure\ 4/T.6).
.RT
.LP
.rs
.sp 13P
.ad r
\fBFigure 4/T.6, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2.3.3
	\fIHorizontal mode\fR 
.sp 9p
.RT
.PP
When this mode is identified, both the run\(hylengths a\d0\ua\d1\uand a\d1\ua\d2\uare 
coded using the 
code words
H\ +\ M(a\d0\ua\d1\u)\ +
M(a\d1\ua\d2\u). H is the flag code word\ 001 taken from the two\(hydimensional
code table (Table\ 1/T.6). M(a\d0\ua\d1\u) and M(a\d1\ua\d2\u) are code words
which represent the length and \*Qcolour\*U of the runs a\d0\ua\d1\uand 
a\d1\ua\d2\urespectively and are taken from the appropriate white or black 
run\(hylength   code
tables (Tables\ 2/T.6 and\ 3/T.6).
.bp
.RT
.ce
\fBH.T. [T1.6]\fR 
.ce
TABLE\ 1/T.6
.ce
\fBCode table\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(42p) | cw(84p) | cw(42p) | cw(60p) .
Mode	Elements to be coded	Notation	Code word
_
.T&
lw(42p) | cw(84p) | cw(42p) | lw(60p) .
Pass	b 1, b 2	P	0001\ \ \ \ \ \ 
_
.T&
lw(42p) | cw(84p) | cw(42p) | lw(60p) .
Horizontal	a 0a 1, a 1a 2	H	 {
001 + M(a
0a
1) + M(a
1a
2)
(see Note)
 }
_
.T&
lw(42p) | lw(54p) | cw(30p) | cw(42p) | lw(60p) , ^  | l | c | c | l 
^  | ^  | c | c | l 
^  | ^  | c | c | l 
^  | c | c | l | c 
^  | ^  | c | l | c 
^  | ^  | c | l | l.
Vertical	a 1 just under b 1	a 1b 1 = 0	V(0)	1\ \ \ \ \ \ \ \ \ 
	a 1 to the right of b 1	a 1b 1 = 1	V R(1)	011\ \ \ \ \ \ \ 	a 1b 1 = 2	V R(2)	000011\ \ \ \ 	a 1b 1 = 3	V R(3)	 {
0000011\ \ \ 
a
1 to the left of b
1
 }	a 1b 1 = 1	V L(1)	010\ \ \ \ \ \ \ 	a 1b 1 = 2	V L(2)	000010\ \ \ \ 	a 1b 1 = 3	V L(3)	0000010\ \ \  \fB	
_
.T&
lw(42p) | lw(126p) | lw(60p) .
Extension		0000001xxx
.TE
.LP
\fINote\fR
\ \(em\ Code M(\ ) of the horizontal mode represents the code words in
Tables 2/T.6 and 3/T.6.
.nr PS 9
.RT
.ad r
\fBTableau 1/T.6 [T1.6], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.sp 24
.bp
.ce
\fBH.T. [T2.6]\fR 
.ce
TABLE\ 2/T.6
.ce
\fBTerminating codes\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
White run length	Code word	Black run length	Code word
_
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 0	00110101	\ 0	0000110111\ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 1	000111\ \ 	\ 1	010\ \ \ \ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 2	0111\ \ \ \ 	\ 2	11\ \ \ \ \ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 3	1000\ \ \ \ 	\ 3	10\ \ \ \ \ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 4	1011\ \ \ \ 	\ 4	011\ \ \ \ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 5	1100\ \ \ \ 	\ 5	0011\ \ \ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 6	1110\ \ \ \ 	\ 6	0010\ \ \ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 7	1111\ \ \ \ 	\ 7	00011\ \ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 8	10011\ \ \ 	\ 8	000101\ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 9	10100\ \ \ 	\ 9	000100\ \ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
10	00111\ \ \ 	10	0000100\ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
11	01000\ \ \ 	11	0000101\ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
12	001000\ \ 	12	0000111\ \ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
13	000011\ \ 	13	00000100\ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
14	110100\ \ 	14	00000111\ \ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
15	110101\ \ 	15	000011000\ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
16	101010\ \ 	16	0000010111\ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
17	101011\ \ 	17	0000011000\ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
18	0100111\ 	18	0000001000\ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
19	0001100\ 	19	00001100111\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
20	0001000\ 	20	00001101000\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
21	0010111\ 	21	00001101100\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
22	0000011\ 	22	00000110111\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
23	0000100\ 	23	00000101000\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
24	0101000\ 	24	00000010111\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
25	0101011\ 	25	00000011000\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
26	0010011\ 	26	000011001010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
27	0100100\ 	27	000011001011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
28	0011000\ 	28	000011001100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
29	00000010	29	000011001101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
30	00000011	30	000001101000
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
31	00011010	31	000001101001
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
32	00011011	32	000001101010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
33	00010010	33	000001101011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
34	00010011	34	000011010010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
35	00010100	35	000011010011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
36	00010101	36	000011010100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
37	00010110	37	000011010101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
38	00010111	38	000011010110
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
39	00101000	39	000011010111
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
40	00101001	40	000001101100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
41	00101010	41	000001101101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
42	00101011	42	000011011010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
43	00101100	43	000011011011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
44	00101101	44	000001010100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
45	00000100	45	000001010101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
46	00000101	46	000001010110
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
47	00001010	47	000001010111
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
48	00001011	48	000001100100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
49	01010010	49	000001100101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
50	01010011	50	000001010010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
51	01010100	51	000001010011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
52	01010101	52	000000100100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
53	00100100	53	000000110111
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
54	00100101	54	000000111000
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
55	01011000	55	000000100111
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
56	01011001	56	000000101000
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
57	01011010	57	000001011000
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
58	01011011	58	000001011001
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
59	01001010	59	000000101011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
60	01001011	60	000000101100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
61	00110010	61	000001011010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
62	00110011	62	000001100110
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
63	00110100	63	000001100111
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 2/T.6 [T2.6], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [T3.6]\fR 
.ce
TABLE\ 3/T.6
.ce
\fBMake\(hyup codes between 64 and 1728\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
White run length	Code word	Black run length	Code word
_
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ \ 64	11011\ \ \ \ \ \ \ 	\ \ 64	0000001111\ \ \ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 128	10010\ \ \ \ \ \ \ 	\ 128	000011001000\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 192	010111\ \ \ \ \ \ 	\ 192	000011001001\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 256	0110111\ \ \ \ \ 	\ 256	000001011011\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 320	00110110\ \ \ \ 	\ 320	000000110011\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 384	00110111\ \ \ \ 	\ 384	000000110100\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 448	01100100\ \ \ \ 	\ 448	000000110101\ 
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 512	01100101\ \ \ \ 	\ 512	0000001101100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 576	01101000\ \ \ \ 	\ 576	0000001101101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 640	01100111\ \ \ \ 	\ 640	0000001001010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 704	011001100\ \ \ 	\ 704	0000001001011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 768	011001101\ \ \ 	\ 768	0000001001100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 832	011010010\ \ \ 	\ 832	0000001001101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 896	011010011\ \ \ 	\ 896	0000001110010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
\ 960	011010100\ \ \ 	\ 960	0000001110011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1024	011010101\ \ \ 	1024	0000001110100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1088	011010110\ \ \ 	1088	0000001110101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1152	011010111\ \ \ 	1152	0000001110110
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1216	011011000\ \ \ 	1216	0000001110111
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1280	011011001\ \ \ 	1280	0000001010010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1344	011011010\ \ \ 	1344	0000001010011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1408\fR	011011011\ \ \ 	1408	0000001010100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1472	010011000\ \ \ 	1472	0000001010101
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1536	010011001\ \ \ 	1536	0000001011010
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1600	010011010\ \ \ 	1600	0000001011011
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1664\fR	011000\ \ \ \ \ \ 	1664	0000001100100
.T&
cw(60p) | cw(54p) | cw(60p) | cw(54p) .
1728	010011011\ \ \ 	1728	0000001100101
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 3/T.6 [T3.6], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.2.4
	\fICoding procedure\fR 
.sp 9p
.RT
.PP
The coding procedure identifies the coding mode that is to be used to code 
each changing element along the coding line. When one of the three 
coding modes has been identified according to Step\ 1 or Step\ 2 mentioned 
below, an appropriate code word is selected from the code table given in 
Table\ 1/T.6. The coding procedure is as shown in the flow diagram of Figure\ 
5/T.6. 
.RT
.LP
.rs
.sp 46P
.ad r
\fBFigure 5/T.6, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
	\fIStep 1\fR 
.sp 9p
.RT
.LP
	i)
	If a pass mode is identified, this is coded using the
word 0001 (Table\ 1/T.6). After this processing, picture
element a`\d0\ujust under b\d2\uis regarded as the new
starting picture element a\d0\ufor the next coding (see
Figure\ 2/T.6).
.LP
	ii)
	If a pass mode is not detected, then proceed to
Step 2.
.LP
	 \fINote\fR \ \(em\ It does not affect compatibility to restrict the use 
of pass mode in the encoder to a single pass mode. Variations of the 
algorithm which do not affect compatibility should be the subject
of further study.
.sp 1P
.LP
	\fIStep 2\fR 
.sp 9p
.RT
.LP
	i)
	Determine the absolute value of the relative distance
a\d1\ub\d1\u.
.LP
	ii)
	 If | | d1\ub\d1\u | \ \(=\ 3, as shown in Table 1/T.6, a\d1\ub\d1\uis 
coded by the vertical mode, after which position\ a\d1\uis 
regarded as the new starting picture element\ a\d0\ufor the
next coding.
.LP
	iii)
	 If | | d1\ub\d1\u | \ >\ 3, as shown in Table 1/T.6, following horizontal 
mode code\ 001, a\d0\ua\d1\uand a\d1\ua\d2\uare 
respectively coded by 
one\(hydimensional run length
coding
.
.LP
	Run lengths in the range of 0 to 63 pels are encoded with their appropriate 
terminating code word
of Table\ 2/T.6. Note that there is a different
list of code words for black and white run lengths. Run lengths in the 
range of 64 to 2623 pels are encoded first by the 
make\(hyup code word
representing the run length which is nearest, not longer, to that required. 
This is then 
followed by the terminating code word representing the difference between 
the required run length and the run length represented by the make\(hyup 
code. Run 
lengths in the range of lengths longer than or equal to 2624\ pels are coded
first by the make\(hyup code of 2560. If the remaining part of the run 
(after the first 
make\(hyup code
of 2560) is 2560 pels or greater, additional make\(hyup code(s) of 2560 
are issued until the remaining part of the run becomes less 
than 2560 pels. Then the remaining part of the run is encoded by terminating
code or by make\(hyup code plus Terminating code according to the range as
mentioned above.
.LP
	After this processing, position a\d2\uis regarded as the new
starting picture element a\d0\ufor the next coding.
.LP
	\fINote\fR \ \(em\ Coding examples are given in Recommendation\ T.4,
\(sc\ 4.2.5.
.sp 2P
.LP
2.2.5
	\fIProcessing the first and last picture element in a line\fR 
.sp 1P
.RT
.sp 1P
.LP
2.2.5.1
	\fIProcessing the first picture element\fR 
.sp 9p
.RT
.PP
The first starting picture element a\d0\uon each coding line
is imaginarily set at a position just before the first picture element, 
and is regarded as a white picture element (see \(sc\ 2.2.2). 
.PP
The first run length on a line a\d0\ua\d1\uis replaced by
a\d0\ua\d1\u\ \(em\ 1. Therefore, if the first actual run is black and 
is deemed to be coded by horizontal mode coding, then the first code word 
M(a\d0\ua\d1\u) 
corresponds to an imaginary white run of zero length (see Figure\ 10/T.4).
.RT
.sp 1P
.LP
2.2.5.2
	\fIProcessing the last picture element\fR 
.sp 9p
.RT
.PP
The coding of the coding line continues until the position of
the imaginary changing element situated just after the last actual element 
has been coded. This may be coded as a\d1\uor \d2\u. Also, if b\d1\uand/or 
b\d2\uare not detected at any time during the coding of the line, they are
positioned on the imaginary changing element situated just after the last
actual picture element on the reference line.
.RT
.sp 2P
.LP
2.3
	 \fIOptional facsimile coding schemes\fR \fI for black and white\fR \fIimages\fR 
.sp 1P
.RT
.sp 1P
.LP
2.3.1
	\fIUncompressed mode\fR 
.sp 9p
.RT
.PP
Uncompressed mode is an optional coding scheme associated to the
basic facsimile coding scheme and is used to transmit the image information
without data compression techniques as shown in Table\ 4/T.6.
.bp
.PP
The extension code in \(sc\ 2.2.4 with the xxx bits set to 111 is
used as an entrance code from the basic coding scheme in \(sc\ 2.2 to the
uncompressed mode.
.PP
While using the uncompressed mode, the last picture elements of the
end of the line and the first picture elements of the beginning of the
following line are concatenated to one pattern.
.RT
.ce
\fBH.T. [T4.6]\fR 
.ce
TABLE\ 4/T.6
.ce
\fBUncompressed mode code words\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(120p) .
 {
Entrance code to
uncompressed mode
 }	 {
Basic coding sheme:\ 0000001111
 }
_
.T&
lw(60p) | cw(60p) | cw(60p) .
Uncompressed  mode code	 {
\fIImage pattern\fR
1\ \ \ \ 
01\ \ \ 
001\ \ 
0001\ 
00001
00000
 }	 {
\fICode word\fR
1\ \ \ \ \ \ \ \ \ \ \ 
01\ \ \ \ \ \ \ \ \ \ 
001\ \ \ \ \ \ \ \ \ 
0001\ \ \ \ \ \ \ \ 
00001\ \ \ \ \ \ \ 
000001\ \ \ \ \ \ 
 }
_
.T&
lw(60p) | cw(60p) | cw(60p) .
 {
Exit from
uncompressed
mode code
 }	 {
\ \ \ \ \ 
0\ \ \ \ 
00\ \ \ 
000\ \ 
0000\ 
 }	 {
0000001T\ \ \ \ 
00000001T\ \ \ 
000000001T\ \ 
0000000001T\ 
00000000001T
T\ denotes a tag bit which tells the colour of the next run
(black = 1, white = 0).
 }
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 4/T.6 [T4.6], p. 
.sp 1P
.RT
.ad b
.RT
.LP
\fI\fR 
.LP
2.4
	\fIFacsimile coding control functions\fR 
.sp 1P
.RT
.sp 2P
.LP
2.4.1
	\fIControl functions for \fR \fIbasic facsimile coding scheme\fR 
.sp 1P
.RT
.sp 1P
.LP
2.4.1.1
	\fIEnd\(hyof\(hyfacsimile block\fR 
.sp 9p
.RT
.PP
The end\(hyof\(hyfacsimile block (EOFB) code is added to the end of
every coded facsimile block. The format of EOFB is as follows:
\v'6p'
.RT
.ce 1000
Format:\ 000000000001000000000001
.ce 0
.sp 1P
.ce 1000
24 bits
.ce 0
.sp 1P
.LP
.sp 1
2.4.1.2
	\fIPad bits\fR 
.sp 9p
.RT
.PP
Pad bits may be used after the end\(hyof\(hyfacsimile block code if it 
is necessary to align on octet boundaries or to a fixed block size. The 
format 
used is as follows.
.PP
Format: Variable length string of 0s.
.RT
.sp 1P
.LP
2.4.1.3
	\fIExtension\fR 
.sp 9p
.RT
.PP
Extension code
is used to indicate the change from the
current mode to another mode, e.g., another coding scheme.
.PP
Format: 0000001xxx,
.PP
where xxx = 111 indicates uncompressed mode which is specified in
\(sc\ 2.3.1.
.PP
Further study is needed to define other unspecified xxx bit
assignments and their use for any further extensions.
.bp
.RT
.sp 2P
.LP
\fB3\fR 	\fBOptional grey scale facsimile coding schemes and their coding\fR 
\fBcontrol functions\fR 
.sp 1P
.RT
.PP
For further study.
.RT
.sp 2P
.LP
\fB4\fR 	\fBOptional colour facsimile coding schemes and their coding\fR 
\fBcontrol functions\fR 
.sp 1P
.RT
.PP
For further study.
.RT
.sp 2P
.LP
\fBRecommendation\ T.10\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBDOCUMENT\ FACSIMILE\ TRANSMISSIONS\fR \fB\ ON\ \fR \fBLEASED\fR  |
\fBTELEPHONE\(hyTYPE\ CIRCUITS\fR 
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.10''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.10	%'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964; amended at Mar del Plata, 1968;\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIat Geneva, 1972, 1976 and 1980)\fR 
.ce 0
.sp 1P
.LP
\fB1\fR 	\fBType of circuits to be used\fR 
.sp 1P
.RT
.PP
The 
telephone\(hytype circuits
used should have
characteristics as recommended in Recommendation\ H.12.
.PP
\fINote\fR \ \(em\ If the leased circuit is used alternately for telephone
conversation and facsimile transmission and if the latter is unidirectional, 
it is not necessary to provide for 
disabling echo suppressors
located on the long\(hydistance leased circuit. However, when such a circuit 
is used for the simultaneous operation in both directions appropriate measures 
should be taken to disable echo suppressors before the actual facsimile 
transmission takes 
place.
.RT
.sp 2P
.LP
\fB2\fR 	\fBModulation\fR 
.sp 1P
.RT
.PP
Equipment conforming to Recommendation\ T.2 or Recommendation\ T.3
may be used. In the case of Recommendation\ T.2 equipment, either amplitude 
or frequency modulation may be chosen. 
.RT
.sp 2P
.LP
\fB3\fR 	\fBPower\fR 
.sp 1P
.RT
.PP
The maximum power output of the transmitting apparatus into the
line shall not exceed 1\ mW whatever the frequency.
.PP
For frequency\(hymodulation equipment conforming to Recommendation T.2, 
the level at the transmitter output shall be so adjusted that the level 
of the facsimile and control signals on the trunk circuit does not exceed 
\(em13\ dBm0 
regardless of the type of operation (duplex or simplex).
.PP
For amplitude\(hymodulation equipment conforming to Recommendation\ T.2, 
higher black levels may be used provided the mean power in any hour, in 
one 
direction of transmission, does not exceed 32\ microwatts (\(em15\ dBm0) 
at the zero relative level point of the trunk circuit. 
.PP
For equipment conforming to Recommendation T.3, higher white levels may 
be used provided the mean power in any hour, in one direction of 
transmission, does not exceed 32\ microwatts (\(em15\ dBm0) at the zero 
relative 
level point of the trunk circuit.
.RT
.sp 2P
.LP
\fB4\fR 	\fBMultipoint transmission\fR 
.sp 1P
.RT
.PP
If facsimile transmissions take place simultaneously from a
transmitting station to several receiving stations, arrangements shall 
be made at the junction points so that, on the circuits following the junction 
points, the same power levels are maintained as those prescribed for individual 
transmissions.
.RT
.sp 2P
.LP
\fB5\fR 	\fBPhase distortion\fR 
.sp 1P
.RT
.PP
Equipment conforming to Recommendation\ T.2 should not require any special 
treatment. However, equipment conforming to Recommendation\ T.3 may 
require 
phase distortion correction
in some cases.
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ T.10\fR  | fIbis\fR 
.RT
.sp 2P
.ce 1000
\fBDOCUMENT\ FACSIMILE\ TRANSMISSIONS\fR \fB\ IN\ THE\ \fR \fBGENERAL\fR 
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.10^bis''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.10^bis	%'
.ce 0
.sp 1P
.ce 1000
\fBSWITCHED\ TELEPHONE\ NETWORK\fR 
.ce 0
.sp 1P
.ce 1000
\fI(Mar del Plata, 1968; amended at Geneva,\fR \fI1972, 1976 and 1980)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR 	\fBType of circuits to be used\fR 
.sp 1P
.RT
.PP
Since 
circuits of the general telephone network
and the
station lines of telephone subscribers should be capable of being used for
document facsimile transmissions on the general network, the circuits to be
used are those of the general switched network which have 2\(hywire terminals 
at both ends of the facsimile station. 
.PP
\fINote\fR \ \(em\ For the actual document transmission, which is one\(hyway,
there is no need to cater for the 
disabling of echo suppressors
.
Compandors
do not seem detrimental to document facsimile
transmission.
.RT
.sp 2P
.LP
\fB2\fR 	\fBOverall loss\fR 
.sp 1P
.RT
.PP
The conditions for overall transmission loss are the same as those for 
circuits of the general switched telephone network. 
.RT
.sp 2P
.LP
\fB3\fR 	\fBModulation\fR 
.sp 1P
.RT
.PP
Equipment conforming to Recommendation T.2 or Recommendation T.3
may be used. In the case of Recommendation\ T.2 equipment, frequency modulation 
shall be used. 
.RT
.sp 2P
.LP
\fB4\fR 	\fBPower\fR 
.sp 1P
.RT
.PP
In order to avoid the risk that facsimile signals be disturbed,
e.g.\ by dial pulses transmitted over adjacent channels or by noise, it is
important that the sending level should be as high as possible, provided,
however, that it shall not exceed \(em13\ dBm0 on the trunk circuit for
frequency\(hymodulation equipment conforming to Recommendation\ T.2 or that the
mean power in any hour, in one direction of transmission, shall not exceed
32\ microwatts (\(em15\ dBm0) at the zero relative level point of the trunk 
circuit for equipment conforming to Recommendation\ T.3. 
.PP
The maximum power output of the transmitting apparatus into the line shall 
not exceed 1\ mW whatever the frequency. 
.RT
.sp 2P
.LP
\fB5\fR 	\fBAmplitude and phase distortion\fR 
.sp 1P
.RT
.PP
Equipment conforming to Recommendation T.2 should not require any special 
treatment. However, equipment conforming to Recommendation\ T.3 may 
require both amplitude and phase distortion correction on certain
connections.
.RT
.LP
.rs
.sp 12P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ T.11\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBPHOTOTELEGRAPH\ TRANSMISSIONS\ ON\ TELEPHONE\(hyTYPE\fR  |
\fBCIRCUIT\fR 
.FS
Recommendation T.11 corresponds to Recommendation
H.41.
.FE
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.11''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.11	%'
.ce 0
.sp 1P
.ce 1000
\fI(former CCIT Recommendation D.3; amended at New Delhi, 1960;\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIGeneva, 1964, 1972 and 1980)\fR 
.ce 0
.sp 1P
.PP
\fINote\fR \ \(em\ In the case of 
carrier circuits
, this
Recommendation applies only to systems established on the basis of
12\(hychannel group
links. Systems using 
16\(hychannel group
links
will be the subject of subsequent study.
.sp 1P
.RT
.sp 2P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that both 
audio\(hyfrequency telephone circuits
and
carrier circuits can be used for phototelegraphy;
.PP
(b)
that when normal audio\(hyfrequency circuits or carrier
circuits are used, amplitude modulation offers some advantages over frequency 
modulation 
.FS
In particular, with the same index of cooperation and speed,
frequency\(hymodulation necessitates a wider frequency range than that of
amplitude\(hymodulation to obtain a picture of the same quality.
.FE
and is therefore to be preferred for phototelegraph transmissions on circuits 
set up from end to end on cable or 
line\(hyof\(hysight radio\(hyrelay
links
.FS
See Recommendation T.15 for phototelegraph transmissions over
combined radio and metallic circuits.
.FE
.
.PP
However, in the case of circuits subject to sudden level variations or 
to noise, frequency modulation may be preferable to amplitude modulation; 
Administrations could in this case come to an agreement to use frequency
modulation for phototelegraph calls over such circuits; the provisions of
Recommendation\ T.1 relative to the frequency\(hymodulation characteristics
should then be applied.
.PP
\fINote\fR \ \(em\ Study Group XV/Joint Working Party LTG mention in
Recommendation\ H.41 that when carrier circuits are used, frequency modulation 
offers advantages over amplitude modulation in that it does not overload 
carrier systems and avoids the influence of sudden level variations or 
noise. It is therefore to be preferred. However, this point should be studied 
further from the 
phototelegraph transmission
point of view.
.RT
.sp 1P
.LP
\fIunanimously declares the view\fR 
.sp 9p
.RT
.PP
that phototelegraph transmissions over 
telephone circuits
require that the following conditions be observed, according to the way in
which the circuits are used for 
phototelegraphy
:
.RT
.sp 2P
.LP
\fB1\fR 	\fBCircuits permanently used for phototelegraphy\fR 
.sp 1P
.RT
.PP
It seems that these circuits are few. In any case, they should even more 
easily meet the characteristics given in \(sc\ 2\ below. 
.RT
.sp 2P
.LP
\fB2\fR 	\fBCircuits used normally (and preferentially) for phototelegraphy\fR 
.sp 1P
.RT
.sp 1P
.LP
2.1
	\fITypes of circuit to be used\fR 
.sp 9p
.RT
.PP
Two\(hywire circuits
have no practical value for phototelegraphy because of feedback phenomena.
.PP
For the same reason, 
4\(hywire circuits
should be extended to the
phototelegraph stations
on a 4\(hywire basis at the appropriate amplifier stations, the terminating 
units and echo\(hysuppressors always being 
disconnected.
.PP
The configuration of a phototelegraph circuit is given in
Figure\ 1/T.11.
.bp
.RT
.LP
.rs
.sp 22P
.ad r
\fBFigure 1/T.11, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2
	\fIOverall loss\fR 
.sp 9p
.RT
.PP
The same conditions apply to the overall transmission loss of
4\(hywire circuits used for phototelegraphy as apply, in general, for
telephony.
.RT
.sp 1P
.LP
2.3
	\fISent signal power\fR 
.sp 9p
.RT
.PP
The emission voltage for the phototelegraph signal corresponding to maximum 
amplitude should be so adjusted that the maximum power level of the 
signal at the zero relative level point is \(em13\ dBm0 for frequency modulation 
phototelegraph transmissions and that the peak signal power level for
amplitude\(hymodulation photo
telegraph transmissions in principle should be
\(em3\ dBm0. In the case of amplitude\(hymodulation, the level of the signal
corresponding to black is usually about\ 30\ dB lower than that of the signal
corresponding to white.
.PP
\fINote\fR \ \(em\ The levels of \(em3 and \(em13\ dBm0 specified above 
are provisional and need further study from the facsimile transmission 
point of view. 
.RT
.sp 1P
.LP
2.4
	\fIRelative levels\fR 
.sp 9p
.RT
.PP
If phototelegraph transmissions take place simultaneously from a
transmitting station to several receiving stations, arrangements shall 
be made at the junction point so that, on the circuits following the junction 
point, 
the same power levels are maintained as those prescribed for individual
transmissions.
.RT
.sp 1P
.LP
2.5
	\fIAttenuation distortion\fR 
.sp 9p
.RT
.PP
The 
limits for attenuation distortion
on international
circuits used for phototelegraphy are given in Recommendation\ G.151 concerning 
telephone circuits. The attenuation distortion between two terminal national 
centres shall therefore not exceed the limits indicated in Recommendation\ 
G.132 and it will not normally be necessary to compensate the distortion 
of the lines linking the phototelegraph stations to the terminal national 
centres in order to obtain, for 
amplitude\(hymodulated phototelegraph transmission
, an
attenuation distortion between phototelegraph stations of less than\ 8.7\ 
dB in the wanted band. 
.bp
.RT
.sp 1P
.LP
2.6
	\fIVariation of circuit overall loss with time\fR  | See Notes\ 1
and\ 2)
.sp 9p
.RT
.PP
2.6.1 
The objective is that:
.sp 9p
.RT
.PP
2.6.1.1
The difference between the mean value and the nominal value
of the transmission loss value should not exceed\ 0.5\ dB.
.PP
2.6.1.2
The standard deviation from the mean value should not
exceed\ 1\ dB.
.PP
However, in the case of circuits set up wholly or partly on
older\(hytype equipment, where the international line consists of two or more
circuit sections, a standard deviation not exceeding\ 1.5\ dB may be
admitted.
.PP
2.6.2
The method for achieving the above objective values is left
to the discretion of Administrations (better maintenance, fitting of automatic 
regulators,\ etc.). 
.PP
2.6.3
The assumption is made that these limits for the variation of loss with 
time of a single circuit may be compared to limits for loss measurements 
made on a set of circuits at a given time. Experience indicates that such 
a 
comparison has a practical validity although it has not been fully demonstrated 
at this time. Administrations are encouraged to use this Recommendation 
as 
giving currently practical limits for sets of circuits. This does not preclude 
the application of these limits to single circuits, should this prove practical 
at any time. 
.PP
\fINote\ 1\fR \ \(em\ See Recommendation\ M.160 and Reference\ [1].
.PP
\fINote\ 2\fR \ \(em\ The provisions specified in \(sc\ 2.6 are provisional and
need further study from the facsimile transmission point of view.
.RT
.sp 1P
.LP
2.7
	\fIPhase distortion\fR  | see also Recommendation\ T.12)
.sp 9p
.RT
.PP
Phase distortion limits the range of satisfactory phototelegraph
transmissions. Differences between the group delays of a telephone circuit, 
in the interval of the phototelegraph transmission, should not exceed 
\v'6p'
.RT
.sp 1P
.ce 1000
\(*D\fIt\fR \(= 
[Unable to Convert Formula]
.ce 0
.sp 1P
.LP
.sp 1
where:
.LP
	\fIf\fR\d\fIp\fR\u	=
	maximum modulation frequency corresponding to the definition and 
scanning speed
.
.sp 1P
.LP
2.8
	\fIInterference\fR 
.sp 9p
.RT
.PP
Interfering currents, whatever their nature, should not exceed the
CCITT recommended limits for telephone circuits.
.RT
.sp 2P
.LP
\fB3\fR 	\fBTelephone circuits rarely used for phototelegraphy\fR 
.sp 1P
.RT
.sp 1P
.LP
3.1
	\fITransmission characteristics\fR 
.sp 9p
.RT
.PP
It seems that the majority of the characteristics specified by the
CCITT for modern telephone circuits are sufficient to permit phototelegraph
transmissions on a circuit chosen at random in a group of circuits normally
used for telephone working. However, it is not certain that such a circuit
would have a sufficiently low phase distortion for such use, particularly
channels\ 1 and\ 12 of a 12\(hycircuit group, use of which is not advised. The
influence of phase distortion is more noticeable in frequency modulation.
.PP
With amplitude modulation there is a further risk that phototelegraph
transmissions will be subject to faulty modulation because the special
precautions applied to circuits regularly used for phototelegraphy
(see \(sc\ 2.6\ above) cannot be applied to circuits taken at random.
.RT
.sp 1P
.LP
3.2
	\fIPrecautions concerning signalling\fR 
.sp 9p
.RT
.PP
As long as automatic switching for phototelegraph circuits is not
envisaged, the signal receiver can be disconnected so that no signalling
disturbances can occur even when frequency modulation is used. However, if
frequency modulation is used for phototelegraph transmission and if it is
impracticable to disconnect the signal receiver, then it would be desirable, 
in the case of the single\(hyfrequency system, that a blocking signal be 
transmitted along with the picture signal to operate the guard circuit 
and render the 
receiver inoperative.
.bp
.PP
It is also apparent that the frequency of such a blocking signal should 
lie well outside the range of frequencies involved in the picture 
transmission.
.PP
The frequency and the level of the blocking signal must depend on the
characteristics of the VF\ receiver (or receivers in the case of a tandem
international connection), as designed by different Administrations to 
meet the specification to be prescribed for international signalling. 
.PP
In the case of the two\(hyfrequency international signalling system, the
CCITT has indicated its view that no interference will take place.
.RT
.sp 2P
.LP
	\fBReference\fR 
.sp 1P
.RT
.LP
[1]
	\fIStatistical theory requirements\fR , Green Book, Vol.\ IV.2,
Supplement\ No.\ 1.6, ITU, Geneva,\ 1973.
.sp 2P
.LP
\fBRecommendation\ T.12\fR 
.RT
.sp 2P
.ce 1000
\fBRANGE\ OF\ \fR \fBPHOTOTELEGRAPH\ TRANSMISSIONS\fR 
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.12''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.12	%'
.ce 0
.sp 1P
.ce 1000
\fBON\ A\ TELEPHONE\(hyTYPE\ CIRCUIT\fR 
.ce 0
.sp 1P
.ce 1000
\fI(former CCIT Recommendation D.3; amended at New Delhi, 1960\fR \fIand 
Geneva, 1964)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.PP
\fINote\fR \ \(em\ In the case of 
carrier circuits
, this
Recommendation applies only to systems established on the basis of
12\(hychannel group
links. Systems using 
16\(hychannel group
links
will be the subject of subsequent study.
.sp 1P
.RT
.sp 2P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that the differences between the delays of the various
frequencies and the width of the transmission band actually usable on a 
circuit for telephony give rise, when phototelegraph signals are started 
or stopped, to transient phenomena which limit the 
phototelegraph transmission speed
;
.PP
(b)
that the range of phototelegraph calls of satisfactory
quality, for a given transmission speed, depends especially on the constitution 
of the circuit, i.e.\ on: 
.LP
	\(em
	the loading and length, in the case of 
audio\(hyfrequency
circuits
;
.LP
	\(em
	 the number of 12\(hychannel group links used in tandem in the case of 
carrier circuits, 
.LP
and on the choice of the carrier frequency for amplitude\(hymodulated photograph 
transmission, or on the mean frequency in the case of frequency modulation; 
.PP
(c)
that phototelegraph transmission of satisfactory quality
requires that the limits of differences between the 
group delays
in the transmitted frequency band, as shown in Figure\ 1/T.12, are not to be
exceeded;
.PP
(d)
that the CCITT has recommended the following for
international telephone circuits:
.PP
the permissible differences for a worldwide chain of twelve
circuits, each set up on a single 
group link
between the minimum group delay throughout the frequency band transmitted 
and the group delay at the 
upper and lower limits of this band are those given in Table\ 1/T.12;
.sp 1P
.LP
\fIunanimously declares the view\fR 
.sp 9p
.RT
.PP
that, as regards the effect of phase distortion on phototelegraph
transmission quality, the carrier frequency (where amplitude modulation is
used) or the mean frequency (when frequency modulation is used) must be 
chosen in such a way that it is as near as possible to the frequency which 
has the 
minimum group delay on the telephone circuit.
.bp
.RT
.LP
.rs
.sp 28P
.ad r
\fBFigure 1/T.12, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.ce
\fBH.T. [T1.12]\fR 
.ce
TABLE\ 1/T.12
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(96p) | cw(42p) | cw(42p) .
	 {
Lower limit
of the
frequency band
 }	 {
Upper limit
of the
frequency band
 }
_
.T&
lw(96p) | cw(42p) | cw(42p) .
International chain	30 ms	15\fB.5\fR  ms
.T&
lw(96p) | cw(42p) | cw(42p) .
 {
Each of the national chain 4\(hywire extensions
 }	15 ms	\ 7.5 ms
.T&
lw(96p) | cw(42p) | cw(42p) .
On the whole 4\(hywire chain	60 ms	30\fB.5\fR  ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/T.12 [T1.12], p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB1\fR 	\fBCircuits permanently used for phototelegraphy\fR 
.sp 1P
.RT
.PP
1.1
It will generally be possible, by agreement between
Administrations, to choose a circuit satisfying stricter limits than those
specified above from the point of view of phase distortion.
.sp 9p
.RT
.PP
1.2
Moreover, it will be possible to compensate 
phase distortions
by inserting 
phase equalizers
and to effect phototelegraph
transmissions occupying the whole nominal band of the circuit.
.bp
.sp 2P
.LP
\fB2\fR 	\fBCircuits used normally (or preferentially) for\fR 
\fBphototelegraphy\fR 
.sp 1P
.RT
.PP
2.1
The greater the differences between the delays in the
transmission intervals, the narrower should be the bandwidth chosen (leading 
to a lower phototelegraph definition or transmission speed). 
.sp 9p
.RT
.PP
2.2
Hence, audio\(hyfrequency circuits should in any case be lightly
loaded circuits.
.PP
2.3
Phase distortion is well within the limits indicated above, in the case 
of carrier circuits, if a single modern\(hytype carrier system is considered 
(and considering especially the telephone channels in the middle of a 
12\(hychannel group of such a system).
.PP
2.4
Nevertheless, it would be unjustifiable from the financial point of view 
to make the aforementioned recommendation concerning phase distortion 
stricter simply with a view to the occasional use of only a few circuits for
high\(hyspeed phototelegraph transmissions
.
.PP
2.5
The curves of Figure\ 2/T.12 give information on the relative
performances of amplitude\(hy and frequency\(hymodulated phototelegraph 
transmissions on audio\(hyfrequency and carrier telephone circuits. 
.LP
.rs
.sp 22P
.ad r
\fBFigure 2/T.12, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB3\fR 	\fBTelephone circuits rarely used for phototelegraphy\fR 
.sp 1P
.RT
.PP
If phototelegraph connections are set up on circuits selected at
random from modern\(hytype groups of telephone circuits (for example, by 
automatic switching), a circuit may be taken which has too high a degree 
of phase 
distortion, particularly if it has been set up on channels\ 1 or\ 12 of a
12\(hychannel group, use of which is deprecated. It is impossible, in this 
case, to draw up general information on the range of phototelegraph transmissions; 
however, it will be possible to meet the conditions for a transmission of
adequate quality if the phototelegraph connection comprises only one 12\(hychannel 
group link and if transmission is effected in normal conditions as outlined 
in Recommendation\ T.1. 
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ T.15\fR 
.RT
.sp 2P
.ce 1000
\fBPHOTOTELEGRAPH\ TRANSMISSION\ OVER\ COMBINED\ RADIO\fR 
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.15''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.15	%'
.ce 0
.sp 1P
.ce 1000
\fBAND\ METALLIC\ CIRCUITS\fR 
.FS
This Recommendation
corresponds to CCIR Recommendation\ 344.
.FE
.ce 0
.sp 1P
.ce 1000
\fI(former CCIT Recommendation D.4; amended at New Delhi, 1960;\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIat Geneva, 1964; Mar del Plata, 1968 and Geneva, 1976)\fR 
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that, to facilitate interworking, it is desirable to
standardize the characteristics of systems employed for phototelegraph
transmission over long\(hydistance HF\ (decametric) circuits
.FS
The transmission over communication\(hysatellite systems will be the subject 
of later study. 
.FE
;
.PP
(b) 
that it is desirable to standardize certain characteristics of the systems 
in such a way as to make them equally suitable for transmission over metallic 
circuits; 
.PP
(c) 
that the transmission system using direct amplitude
modulation is generally unsatisfactory over HF\ (decametric) radio circuits,
because of the intolerable fading ratio usually encountered;
.PP
(d) 
that the system of sub\(hycarrier frequency modulation has
proved satisfactory, but requires standardization in respect of the centre
frequency and shift frequencies, taking into account the values of the
picture\(hymodulation frequencies to be transmitted;
.PP
(e) 
that, when a direct frequency\(hymodulation system is employed, the terminal 
equipment normally used for a sub\(hycarrier modulation system should be 
usuable without serious modifications; 
.PP
(f
)
that, taking into account the quality necessary for reproduction of the 
picture received, the effect of multipath echoes on 
long\(hydistance HF\ (decametric) radio circuits normally limits the maximum
admissible picture\(hymodulation frequency to approximately 600\ Hz,
.sp 1P
.LP
\fIunanimously declares the view\fR 
.sp 9p
.RT
.PP
that phototelegraph transmissions over combined radio and metallic
circuits should conform to the following provisions:
.RT
.sp 2P
.LP
\fB1\fR 	\fBCharacteristics of radio circuits\fR 
.sp 1P
.RT
.PP
1.1
When a sub\(hycarrier frequency\(hymodulation system is used, the
following characteristics should be observed:
.sp 9p
.RT
.ad r
	centre frequency
1900\ Hz
.ad b
.RT
.ad r
		frequency corresponding to white
1500\ Hz
.ad b
.RT
.ad r
		frequency corresponding to black
2300\ Hz
.ad b
.RT
.PP
	(the 1500\(hyHz frequency is also used for the phasing signal)
.LP
.sp 5
.bp
.PP
1.2
When a direct frequency\(hymodulation system is employed, the
following characteristics should be observed:
.sp 9p
.RT
.ad r
	centre frequency (corresponding to assigned
frequency)
\fIf\fR\d0\u\ \ \ \ \ \ \ \  |
.ad b
.RT
.ad r
		frequency corresponding to
white
\fIf\fR\d0\u\ \(em\ 400\ Hz
.ad b
.RT
.ad r
		frequency corresponding to
black
\fIf\fR\d0\u\ +\ 400\ Hz
.ad b
.RT
.PP
	(the frequency \fIf\fR\d0\u\ \(em\ 400\ Hz is also used for the phasing
signal)
.PP
1.3
In both systems the 
stability of frequencies
should be
such that the variations are less than:
.sp 9p
.RT
.LP
	\ 8\ Hz during a period of 1\ second,
.LP
	16\ Hz during a period of 15\ minutes.
.sp 2P
.LP
\fB2\fR 	\fBCharacteristics of equipment and metallic circuits\fR 
.sp 1P
.RT
.PP
The standards for 
phototelegraph apparatus
and the
specifications for transmission on metallic circuits are given in
Recommendations\ T.1 and\ T.11.
.PP
On the metallic sections connected to both ends of the radio path,
frequency modulation can be used whatever type of modulation is used over 
the radio circuits. However, amplitude modulation should preferably be 
used (see 
Recommendation\ T.11 on this subject).
.RT
.sp 2P
.LP
\fB3\fR 	\fBTypical circuit\fR 
.sp 1P
.RT
.PP
In principle, a worldwide hypothetical connection consisting of
combined radio and wire channels may involve a maximum of two radio circuits
with two metallic circuits at either end. Another metallic circuit may be
required in the radio channel link if, in a country, the receiving and
transmitting radio stations are at a distance from each other or if the two
radio circuits terminate in neighbouring countries. The typical circuit for
this connection is shown in Figure\ 1/T.15.
.PP
The frequency tolerances on each of the various sections of this
connection should be no greater than those proposed by the CCITT (see
Recommendations\ G.225 and\ T.1) as shown in Figure\ 1/T.15.
.RT
.LP
.rs
.sp 18P
.ad r
\fBFigure 1/T.15, (M), p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
If it is assumed that these deviations are distributed at random and if 
we take the standard deviation, we shall obtain the values\ 15 and 28\ 
Hz 
respectively, which are not harmful for satisfactory reception, since CCITT
Recommendation\ T.1 admits a maximum deviation of 32\ Hz.
.sp 2P
.LP
\fB4\fR 	\fBModulation conversion\fR 
.sp 1P
.RT
.PP
When conversion from amplitude modulation to frequency modulation (or vice 
versa) is required, the conversion should be such that the deviation of 
the frequency\(hymodulated carrier varies linearly with the amplitude of the
amplitude\(hymodulated carrier.
.PP
Each Administration will decide, when the question arises, on the
location of modulation converters. They may be placed either at the terminal
phototelegraph station or at the control station associated with the radio
station, to facilitate speech on the circuit used for phototelegraphy, 
if the radio channel will carry speech. 
.RT
.sp 2P
.LP
\fBRecommendation\ T.20\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSTANDARDIZED\ TEST\ CHART\ FOR\ FACSIMILE\ TRANSMISSIONS\fR 
.FS
With the standardization of two test charts for document facsimile transmission 
(Test 
charts Nos.\ 2 and\ 3) in Recommendation\ T.21, this chart will be designated 
as \*QTest chart No.\ 1\*U. 
.FE
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.20''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.20	%'
.ce 0
.sp 1P
.ce 1000
\fI(New Delhi, 1960; amended at Geneva, 1964\fR \fIand Mar del Plata, 1968)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
that it will be a great advantage to use a standardized test chart to check 
the quality of facsimile transmissions and that such a chart would 
provide the receiving office with a reliable and rapid means of checking the
quality of test transmissions according to uniform principles and of making
comparisons between different transmission results in a precise way. The 
chart has been designed for measuring the quality of both picture and black\(hyand\(hywhite 
transmissions and it enables the apparatus used and the communication channels 
to be judged by means of objective measurements, the results of which may 
be 
expressed in code.
.RT
.sp 1P
.LP
\fIunanimously declares the view
.sp 9p
.RT
.PP
(1) 
that tests of facsimile transmission quality will be carried out in the 
international service with the aid of the \*QCCITT standardized test chart\*U. 
.PP
(2) 
that this test chart is made by the ITU under the
supervision of the CCITT and should be offered for sale by the ITU. There 
are two editions: 
.LP
	\(em
	 test charts sold before the IVth Plenary Assembly of the CCITT (October\ 
1968) are of the first edition; 
.LP
	\(em
	 test charts sold since the IVth Plenary Assembly of the CCITT are of 
the second edition. 
.PP
These test charts are described in the annex to this Recommendation; the 
specimens printed in the annex cannot be used for measurements. 
.PP
(3)
that these two test charts are compatible and a test chart of either the 
first edition or the second can be used in the international 
service.
.LP
.sp 3
.bp
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation T.20)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDescription of the\fR 
\fBstandardized test chart No. 1\fR 
.sp 1P
.RT
.ce 0
.PP
A.1
The test chart No. 1 has the following dimensions:
.sp 1P
.RT
.LP
	\(em
	length: 250\ mm,
.LP
	\(em
	width: 110\ mm.
.PP
The lateral margin is some 10\ mm wide on either side. The margin at top 
and bottom is 20\ mm wide, approximately. The chart is divided into sections 
marked on the transparent paper delivered with every chart. 
.PP
A.2
Sections\ 1 and\ 2 contain two tone scales, each having
15\ density steps, varying from black and white and vice versa. Nos.\ 1, 4, 8,
11, and\ 15 bear their numbers on them, the number\ 1 always betokens white 
and the number\ 15 black. 
.sp 9p
.RT
.PP
A.3
Section\ 3 is occupied by a group of black lines on a white
background, in the form of hyperbolae. The thickness of the lines and the
distances between them diminish regularly from left to right, from 1\ mm to
1/6\ mm.
.sp 9p
.RT
.PP
If a vertical line be drawn through the hyperbolae, the lines
therein will subtend distances on the vertical line equal to the inverse 
of the figures on the scale graduated from\ 1 to\ 6 at the bottom of Section\ 
3. 
.PP
A.4
Section\ 4 contains two groups of hyperbolae similar to those of Section\ 
3 but limited to the scanning densities lying between\ 3 and\ 6. One 
group is made up of grey lines on a white ground, the other by grey lines 
on a black ground. 
.sp 9p
.RT
.PP
A.5
Section\ 5 contains three patterns.
.sp 9p
.RT
.LP
	a)
	\fIFirst edition\fR 
.LP
	 The first pattern is made up of five black lines on a white background, 
the lines being 0.25\ mm thick, arranged in one group of two lines and 
another of three lines. These lines are 0.25\ mm apart, and the two groups 
are separated by 1.5\ mm. 
.LP
	 The second pattern is the same as the first, but the lines are white 
on a black background. 
.LP
	The third pattern consists of two similar groups of black
lines on a white background, as follows:
.ad r
	\(em
	line, thickness
1\ mm |  \ 
.ad b
.RT
.ad r
		\(em
	separation
0.25\ mm
.ad b
.RT
.ad r
		\(em
	line, thickness
0.25\ mm
.ad b
.RT
.ad r
		\(em
	separation
1\ mm |  \ 
.ad b
.RT
.ad r
		\(em
	line, thickness
0.25\ mm
.ad b
.RT
.ad r
		\(em
	separation
0.25\ mm
.ad b
.RT
.ad r
		\(em
	line, thickness
1\ mm |  \ 
.ad b
.RT
.LP
		The two groups are separated by 1\ mm.
.LP
	b)
	\fISecond edition\fR 
.LP
	 The first pattern is made up of eight black lines on a white background, 
separating into three groups: 
.LP
	\(em
	one group of two black lines being 0.25\ mm thick
and 0.25\ mm apart;
.LP
	\(em
	one group of three black lines being 0.25\ mm thick
and 0.25\ mm apart;
.LP
	\(em
	one group of three black lines being 0.1\ mm thick
and 0.25\ mm apart.
.LP
	These groups are separated by 1.5\ mm.
.LP
	The second and third patterns are respectively the same as
those of Section\ 5 of the first edition.
.bp
.PP
A.6
Section 6 contains a tapering black line on a white background, and a tapering 
white line on a black background. The maximum width of the 
tapering lines is\ 0.7\ mm.
.sp 9p
.RT
.PP
At the top of the section is a scale in millimetres, showing the
width of the tapering lines.
.PP
A.7
Section 7 contains a strip of tone equivalent to that in
Section\ 1, step\ 11, on a background of Section\ 1, step\ 5.
.sp 9p
.RT
.PP
A.8
In the first edition, Section\ 8 accommodates a photograph of
UNESCO House in Paris.
.sp 9p
.RT
.PP
In the second edition, Section\ 8 accommodates a portrait of an
Argentine boy.
.PP
A.9
Section 9 contains two concentric circles, the radii of which
differ by 1\ mm. A square, with its diagonals, is inscribed in the inner
circle.
.sp 9p
.RT
.PP
In the second edition the radii of the two circles are bigger than those 
of the first edition and the exterior circle is osculating with the 
limits of Section\ 9.
.PP
A.10
There are two Sections numbered\ 10 which contain adjustment
lines.
.sp 9p
.RT
.PP
In the first edition, these lines are numbered from\ 1 to\ 6 and these 
figures are placed in the central part of the left half of Section\ 10. 
.PP
In the second edition, only the even adjustment lines are numbered and 
these figures are placed at the left of the prolongation of the line separating 
Sections\ 3 and\ 12, 7 and\ 12 respectively. 
.RT
.PP
A.11
Section 11 contains a pattern of lines, with a spacing of
2.5\ mm. It is divided into two equal parts by a vertical line. The column on
the right contains white rectangles, while that on the left contains alternate 
white and black rectangles. 
.sp 9p
.RT
.PP
In the second edition Section 11 is so cut that the parts adjacent to Sections\ 
10 are kept in white. These parts are used for extension of the 
adjustment lines of Sections\ 10.
.PP
To indicate the centre of the test charts of the second edition, a line 
in the right column of Section\ 11 which is the prolongation of the line 
separating the density steps\ 8 and\ 9 of Section\ 1 is 0.5\ mm thick.
.RT
.PP
A.12
Section\ 12 contains letters, digits, and punctuation marks
printed in various styles, and arranged so that they can be read sideways.
.sp 9p
.RT
.PP
Section\ 12 is divided into three parts:
.LP
	\(em
	 the bottom part contains typographical signs (letters, figures, and a 
few punctuation marks), printed in various styles. 
.LP
	\(em
	the middle part contains signs in typewritten characters 2.3\ mm high.
.LP
	\(em
	 the top part contains two words: \*QTEST\*U and \*QINTERNATIONAL\*U one 
above the other. \*QTEST\*U is black on a white background, while 
\*QINTERNATIONAL\*U is white on a black background.
.PP
A.13
Section\ 13 contains
.sp 9p
.RT
.LP
	\(em
	space for the name of the transmitting station;
.LP
	\(em
	the cooperation indices most often used;
.LP
	\(em
	the diameters in millimetres of the drums most often used;
.LP
	\(em
	the r.m.p. of the drums;
.LP
	\(em
	\*QMod.: AM FM\*U to indicate either amplitude modulation or
frequency modulation (the second edition only);
.LP
	\(em
	 the indication \*QCCITT\*U in the test charts of the first edition is 
replaced by \*QCCITT\ 2\*U for the test charts of the second 
edition.
.LP
.rs
.sp 4P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure MIRE No 1, p.15\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ T.21\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSTANDARDIZED\ \fR \fBTEST\ CHARTS\ FOR\ DOCUMENT\ FACSIMILE\fR  |
\fBTRANSMISSIONS\fR 
.EF '%	Fascicle\ VII.3\ \(em\ Rec.\ T.21''
.OF '''Fascicle\ VII.3\ \(em\ Rec.\ T.21	%'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1980)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a) 
that a standardized test chart to check the quality of
document facsimile transmissions will have great advantages. Owing to the
development of international document facsimile transmission services, 
a great variety of characters and symbols, including ideographic symbols, 
are involved and must be taken into consideration. 
.PP
(b) 
that the many different reasons for conducting the test has led to the 
definition of two test charts: 
.LP
	\(em
	one, \*Q
transmission test chart
\*U for evaluating the
make\(hyup of the page and the legibility of the text in the various
languages used by the ITU;
.LP
	\(em
	the other, \*Q
characterization test chart
\*U for the
evaluation of the technical quality parameters enabling the technicians
to detect any faults;
.sp 1P
.LP
\fIunanimously adopts the view\fR 
.sp 9p
.RT
.PP
(1) 
that tests of document facsimile transmission quality should be carried 
out in the international service using the CCITT standardized test charts; 
.PP
(2) 
that these test charts should be produced by the ITU under the supervision 
of the CCITT and should be offered for sale by the ITU. There are two types 
of charts: 
.LP
	\(em
	\*QTest chart No. 2: Transmission test\*U intended for the
general evaluation of legibility,
.LP
	\(em
	 \*QTest chart No. 3: Characterization test\*U intended to check the quality 
parameters of apparatus. 
.PP
The charts are described in Annex\ A; the specimens printed in
Annex\ A cannot be used for measurements;
.PP
(3)
that the charts should be used with facsimile apparatus in accordance with 
Recommendations\ T.2, T.3 and\ T.4. 
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation T.21)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDescription of the standardized document facsimile test charts\fR 
.sp 1P
.RT
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\fB1\fR 	\fBDimensions of the test charts\fR 
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	\(em
	length: 297 mm
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	\(em
	width: 210 mm
.PP
They are divided into sections marked:
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	\(em
	2.1 \(hy 2.16 on the Test chart No. 2 for transmission test,
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	\(em
	3.1 \(hy 3.23 on the Test chart No. 3 for characterization
test.
.PP
These section markings are also used to designate the following paragraphs 
which describe the given section. 
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.PP
The characterization test chart is prepared by a process using a small 
frame in order to simplify production. 
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\fB2\fR 	\fBTest chart No. 2: Transmission test\fR 
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This test chart contains elements permitting quantitative evaluations of 
distortion and character groups intended for evaluation of the readability 
of the facsimile document. 
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2.1
	\fI4 groups of arrows and lines\fR 
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These groups permit evaluation of framing distortions of the
facsimile document appearing as lost margins.
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2.2
	\fIAlternating black\(hywhite lines, thickness 0.5 mm\fR 
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The black lines on the facsimile document must be separated: this is the 
test of minimum acceptable definition. 
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2.3
	\fI2 sets of 1 black band and 1 white band\fR 
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Limits of horizontal resolution for isolated black and white lines. The 
numbers placed between the two bands indicate thicknesses in microns. 
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2.4
	\fIDiagonal line\fR 
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This line permits evaluation of sweep uniformity over the entire
test\(hypattern surface.
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2.5\(hy2.6
	\fIBlack circles and concentric circles with two perpendicular\fR 
\fIdiameters\fR 
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Flattening of circles along either diameter indicates differences between 
the transmitting and receiving devices, either in the selection of 
horizontal and vertical definitions or in the index of cooperation.
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2.7
	\fIHorizontal band\fR 
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Permits evaluation of vertical definition.
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2.8
	\fIRandom characters\fR 
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The characters are in \*QUnivers 8 points\*U and \*QEnglish Times 8
points\*U.
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Certain characters are arranged in a vertical line. These groups must be 
reproduced legibly by all facsimile machines. 
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2.9\ to\ 2.14
	\fITexts in English \(em French \(em Spanish \(em Chinese \(em\fR 
\fIArabic \(em Russian\fR 
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They permit evaluation of the overall quality of the
transmitter\(hyreceiver system by examination of the limits of readability 
for the small characters. 
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2.15
	\fIEmpty box\fR 
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Special typed or handwritten texts may be entered in this box, as required 
by users. 
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2.16
	\fI4 scales with millimetre graduations\fR 
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.PP
These scales permit determination of distortions in length on
horizontal and vertical lines by direct measurement with a graduated
rule.
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\fB3\fR 	\fBTest chart No. 3: Characterization test\fR 
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.PP
This test chart permits a definition of the quantizeable limits in the 
performance of facsimile machines (half\(hytone, framing, definition,\ 
etc.). 
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This is a reference for the drafting of lists of characteristics for CCITT 
Recommendations or of technical specifications. 
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As such, this test chart is intended for facsimile\(hymachine adjustment 
and maintenance operations. 
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3.1
	\fIBand of alternating black and white lines, thickness 5 mm\fR 
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Permits measurement of scanning distortion and adjustment of the
black and white levels.
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3.2
	\fI2 density level bands in complementary order\fR 
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These scales permit measurement of the scanners' analogue response curves 
and definition of the white/black decision threshold level in digital 
transmission devices.
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The two bands, covering nearly the width of the page, are reversed for 
verification of the uniformity of the scanner's response over the entire 
length of the horizontal line. 
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The densities, varying between 0.2 and 1.5, are indicated in the
margin of each of the bands.
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3.3
	\fIBlack band covering the entire page width\fR 
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Permits adjustment of characteristic \*Qblack\*U signals through the
entire sequence of the electronic devices.
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3.4\(hy3.5
	\fIIsolated black and white lines, variable thickness,\fR 
\fI2 complementary bands\fR 
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Using this group, it is possible to define the limits of resolution for 
isolated black and white lines. 
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Line thicknesses are indicated in microns.
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3.6
	\fIBand of alternating lines, 8 lines per mm (black and white line\fR 
\fIthickness 125\ microns)\fR 
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Obliqueness: 2\(de
.PP
This band permits verification of the optical definition of integrated 
1728\(hypoint scanners. 
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Obliqueness is required in order to obtain, during test pattern
advance, a situation in which the points of the image are perfectly centred 
on the detector's photosensitive cells where the modulation depth is at 
a 
maximum.
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3.7\(hy3.8
	 \fIStrips of alternating lines, 6 lines per mm (black and white\fR \fIline 
thickness 166.6\ microns)\fR 
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Zone 3.7 consists of lines with an obliqueness of 3\(de.
.PP
Zone 3.8 consists of vertical lines.
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Zone 3.7 has the same purpose as zone 3.6, but less severe.
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Zone 3.8 permits examination of limits of definition.
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3.9
	 \fIAlternating lines, 4 lines per mm (black and white line thickness\fR 
\fI250\ microns)\fR 
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Permits verification of standardized facsimile\(hymachine definition.
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The black lines on the received copy must be separated.
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3.10
	 \fIAlternating lines, 2 lines per mm (black and white line thickness\fR 
\fI500\ microns)\fR 
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.PP
This scale represents the minimum permittable definition for a
facsimile machine. The black lines on the facsimile document must be clearly
separated.
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3.11
	\fIVertical and horizontal bundles (converging patterns)\fR 
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This group of 3 bundles of converging lines permits quantization of the 
limits of horizontal and vertical definitions. 
.PP
The numbers shown along the bundles indicate the thickness of black
and white lines in microns.
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3.12
	\fIDiagonal line\fR 
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This line is designed for evaluation of sweep uniformity over the entire 
test chart surface. 
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3.13
	\fIBlack lines, thickness 250 microns, spaced 750 microns\fR 
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3.14
	\fIBlack lines, thickness 250 microns, spaced 1000 microns\fR 
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The two scales of 3.13 and 3.14 simulate character downstrokes.
They must be faithfully reproduced by facsimile.
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3.15
	\fIBlack spindle and white spindle\fR 
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Permits quantization of the limits of horizontal resolution for
isolated black and white lines. The numbers shown along the band indicate 
line thicknesses in microns. 
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3.16
	\fI2 vertical lines, thickness 250 microns, spacing 1000 microns\fR 
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The purpose of this group of 2 lines is the evaluation of
longitudinal jitter effect. The value of the jitter effect may be quantized 
by measurement of the minimum dimension reached at the spacing between 
the two 
lines.
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3.17
	\fIDecreasing\(hydensity character set\fR 
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This group of characters permits examination of the limits of
reproducible density. Results obtained yield information on the effectiveness 
of adaptive thresholds. They also permit definition of unusable document 
types, due either to insufficient relative density of characters (e.g.,\ hard
pencils), or to inadequate character size, or to a combination of these two
parameters.
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3.18
	\fIISO characters\fR  | cf NFZ 43006 \(hy June 1965)
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Correct identification of the ISO character is a guarantee of
satisfactory imaging of comparable typographic characters.  They therefore
permit completely objective readability tests.
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3.19
	\fIRandom characters\fR 
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Some of the characters are in \*QUnivers 6 point\*U font.
The characters are arranged in two groups:
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	\(em
	a first group along horizontal lines, positioned in the
lower part of the test pattern;
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	\(em
	a second group along vertical lines, positioned in the
centre of the test pattern.
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These characters permit qualitative evaluation of readability.
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3.20
	\fIGroup of Chinese, Russian and Arabic characters\fR 
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This group completes the group of 3.11 and 3.19 for evaluations of readability 
of Chinese, Russian and Arabic characters. 
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3.21
	\fI4 scales, graduation in millimetres\fR 
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.PP
These scales permit determination of distortions in length of
horizontal and vertical lines by direct measurement with a graduated
rule.
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3.22
	\fI4 groups of arrows and lines\fR 
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.PP
These groups permit quantization of framing defects of the
facsimile document.
.PP
The numbers indicate distances in millimetres measured from the edge of 
the test pattern. 
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3.23
	\fIFrame A` A B B`\fR 
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.PP
This frame permits measurement of parallelogram deformation of the image 
caused by time\(hybase frequency differences. 
.PP
A square placed on A B B`, with one side aligned with AB, intercepts line 
A` B` at a point B". 
.PP
Quantization may take the form of a value in millimetres for the
distance\ B` B".
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.rs
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\fBFigure MIRE No 2, p.\fR 
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.rs
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\fBFigure MIRE No 3, p.\fR 
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