ISO/IEC 9637-1:1994

ISO/IEC
INTERNATIONAL
9637-l
STANDARD
First edition
1994-03-01
Information technology - Computer
- Interfacing techniques for
graphics
dialogues with graphical devices (CGI) -
Data stream binding -
Part 1:
Character encoding
Technologies de /‘information - Infographie - Techniques
intetiaciales de dialogues avec dispositifs graphiques (CGI) - liaison
de courant D -
Partie 7: Codage des caractbres
Reference number
ISO/IEC 9637-1:1994(E)

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0 ISO/IEC
ISO/IEC 9637~1:1994 (E)
CGI Character Encoding
Contents
Contents
iv
Foreword .
V
...............................................................................................................
Introduction
V
...............................................................................
0’1 . Purpose of the character encoding
V
02 . Objectives .
V
...........................................................
03 . Relationship to other International Standards
1
1 Scope .
2
Normative references .
2
3
Notational conventions .
3
3
7-Bit and 8-Bit code tables .
31 .
....................................................................... 4
Code extension techniques vocabulary
32
4
CO sets .
3'2 . 1
4
Cl sets .
3'2 . 2
4
G sets .
3'2 . . 3
6
Overall structure .
4
6
.................................................................................
41 . General form of the data stream
6
...............................................................
42 Entering and leaving the CGI environment
6
...................................................................
4:2.1 Implicitly entering the CGI environment
..................
6
4.2.2 Designating and invoking the CGI coding environment from IS0 2022
6
......................................................................................................
43 . Encoding functions
................................................................................. 8
Method of encoding opcodes
5
8
Encoding technique of the basic opcode set .
51 .
9
Extension mechanism .
52 .
9
Opcode assignments .
53 .
9
..................................................................................
54 . Opcodes for soliciting functions
20
.........................................................................
6 Method of encoding parameters
21
61 . Basic format .
21
62 . Bitstream format .
22
Coding integers (I, IF8, IF16, IF32) .
63 .
23
Coding real numbers (R) .
64 .
........................................ 25
Coding Virtual Device Coordinates and Points (VDC, P)
65 .
26
.............................................................................
66 Coding point list parameters (nP)
26
....................................................................................................
6'6 . 1 Displacement mode
26
......................................................................................................
6'6 . 2 Incremental mode
31
6'6 . . 3 Incremental mode encoding .
31
67 . Colour specifiers (CI, CD) .
32
68 Colour lists (nC1, nCD) .
33
6'8 . 1 Normal format (coding type=O) .
33
Bitstream format (coding type=l) .
6'8 . 2
34
Runlength format (coding type=2) .
6'8 . 3
34
...........................................................
6'8 . . 4 Runlength bitstream format (coding type=3)
o ISO/IEC 1994
All rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, clcctronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
ISO/IEC Copyright Office l Case postale 56 l CH-1211 Genkve 20 l Switzerland
Printed in Switzerland
ii

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@ ISO/IEC ISO/IEC 963711:1994 (E)
Contents
CGI Character Encoding
34
6.8.5 Examples .
69 String arameters (S, SF) . 36
6'9 . 1 Overal P string parameter format . 36
36
6'9 . 2 Bit combinations permitted within string parameters of text functions .
6'9 . 3 CO control within string parameters . 37
6'9 4 Using G-sets in string parameters . 37
6:9:4.1 String parameters and character sets . 37
6.9.4.2 String parameters of other CGI functions . 38
6.10 Enumerated parameters (E) . 38
6.11 Index parameters (IX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Client-specified name parameters (CSN) . 39
6.12
6.13 Input colour parameters (ICO, nIC0) . 40
Data record parameters (D) . 40
6.14
Character substitution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7
8 Representation of CGI functions . 44
81 . Soliciting functions . 44
82 . Enumerated parameters . 45
83 Functions not specified in ISO/IEC 9636 . 45
8'3 . 1 DOMAIN RING . 45
8'3 . 2 INTEGER PRECISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
8'3 . 3 REAL PRECISION ~. 46
. INDEX PRECISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
8'3 4
COLOUR PRECISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
8'3 . 5
8'3 . 6 COLOUR INDEX PRECISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
VDC INTEGER PRECISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
8'3 . 7
VDC REAL PRECISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
8'3 . 8
8'3 . . 9 CLIENT SPECIFIED NAME PRECISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Encoding of matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
84 .
Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9
10 Classification and designation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Annex Ar List of CGI Opcodes . 52
Annex B: List of escape sequences . 63
0.0
111

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ISO/IEC 9637-lt1994 (E) @ ISO/IEC
Foreword CGI Character Encoding
Foreword
for Standardization) and IEC (the
IS0 (the International Organization
International Electrotechnical Commission) form the specialized system for
worldwide standardization. National bodies that are members of IS0 or IEC
participate in the development of International Standards through technical
committees established by the respective organization to deal with particular
fields of technical activity. IS0 and IEC technical committees collaborate in
fields of mutual interest. Other international organizations, governmental and
non-governmental, in liaison with IS0 and IEC, also take part in the work.
In the field of information technology, IS0 and IEC have established a joint
technical committee, ISO/IEC JTC 1. Draft International Standards adopted by
the joint technical committee are circulated to national bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the
national bodies casting a vote.
International Standard ISO/IEC 9637-l was prepared by Joint Technical
Committee ISO/IEC JTC 1, Information technology, Sub-Committee SC 24,
Computer graphics and image processing, in collaboration with the European
Computer Manufacturers Association (ECMA) and the European Conference of
Postal and Telecommunications Administration (CEPT).
ISO/lEC 9637 consists of the following parts, under the general title Information
Computer graphics - Interfacing techniques for dialogues with
technology -
graphical devices (CGI) - Data stream binding:
- Part 1: Character encoding
- Part 2: Binary encoding
- Part 3: Clear text encoding
Annexes A and B of this part of ISO/IEC 9637 are for information only.
iv

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@ 1s0/xEc
ISO/IEC 9637~ltl994 (E)
CGI Character Encoding
Introduction
Introduction
0.1 Purpose of the character encoding
The character encoding of the Computer Graphics Interface (CGI) provides a data stream represen-
tation of the CGI function syntax intended for situations in which it is important to minimize the
size of the encoded data or transmit the data through character-oriented communications services.
The encoding uses compact representation of data that is optimized for storage or transfer between
computer systems.
If minimizing the processing overhead is more important than data compaction, an encoding such
as the binary encoding contained in ISO/IEC 9637-2 may be more appropriate.
0.2 Objectives
This encoding was designed with the following objectives:
a) regular syntax: All CGI functions are encoded in a uniform way so that parsing the en-
coded data is simple;
compactness: the encoding provides a highly compact data stream, suitable for systems
b)
with restricted storage capacity or transfer bandwidth
c) extensibility: the encoding allows for future extensions;
d) transportability: the encoding is suitable for use with transport mechanisms designed
for character-oriented data based on a standard national character set derived from
ISO/IEC 646.
0.3 Relationship to other International Standards
The character encoding has been developed in collaboration with the ISO/EIC JTClBC2. The en-
coding conforms to the rules for code extension specified in IS0 2022 in the category of complete
coding system.
The representation of character data in this part of ISO/IEC 9637 follows the rules of ISO/IEC 646
and IS0 2022.
For certain functions, ISO/IEC 9636 defmes value ranges as being reserved for registration. The
values and their meanings will be defined using the established registration procedures (see
ISO/IEC 9636-l).
This encoding is based on that for the Computer Graphics Metafile ISO/IEC 8632-2. Wherever pos-
sible, the opcodes and parameter representations of CGM elements have been followed.
V

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@ ISO/IEC
CGI Character Encoding
Introduction
vi

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INTERNATIONAL STANDARD @ IsO/IEC
ISOhEC 9637=1:1994(E)
Information technology - Computer graphics
- Interfacing
techniques for dialogues with graphical devices (CGI) -
Data
stream binding -
Part 1:
Character encoding
1 Scope
This part of ISO/IEC 9637 specifies a character encoding of the Computer Graphics Interface. For
each of the functions specified in ISO/IEC 9636 an encoding is specified.
This encoding of the Computer Graphics Interface provides a highly compact representation of the
data, suitable for applications that require the data to be of minimum size and suitable for trans-
mission with character-oriented transmission services.

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ISO/IEC 9637-lrl994 (E) @ ISO/IEC
2 Normative references CGI Character Encoding
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provi-
sions of this part of ISO/IEC 9637. At the time of publication the editions indicated were valid. All
standards are subject to revision, and parties to agreements based to this part of ISO/IEC 9637 are
encouraged to investigate the possibility of applying the most recent editions of the standards listed
below. Members of IS0 and IEC maintain registers of currently valid international standards.
ISO/IEC 646:1991, Information technology - IS0 7-bit coded character set for information in-
terchange.
IS0 7-bit and 8-bit coded character sets - Coded
IS0 2022:1986, Information processing -
extension techniques.
IS0 23751985, Data processing - Procedure for registration of escape sequences.
Control functions for coded character sets.
ISO/IEC 6429:1992, Information technology -
IS0 7942:1985, Information processing systems - Computer graphics - Graphical Kernel
System (GKS) functional description.
ISO/IEC 8632-2: 1992, Information technology - Computer graphics - Metafile for the storage and
transfer ofpicture description information - Part 2 : Character encoding.
ISO/IEC 9636-1:1991, Information technology - Computer graphics - Interfacing techniques for
dialogues with graphical devices (CGI) - Functional specification - Part 1:
Overview, profiles and conformance.
ISO/IEC 9636-2:1991, Information technology - Computer graphics - Interfacing techniques for
dialogues with graphical devices (CGI) - Functional specification - Part 2:
Control.
ISOLIEC 9636-3:1991, Information technology - Computer graphics - Interfacing techniques for
dialogues with graphical devices (CGI) - Functional specification - Part 3:
output.
ISO/IEC 9636-4:1991, Information technology - Computer graphics - Interfacing techniques for
dialogues with graphical devices (CGI) - Functional specification - Part 4:
Segments.
ISO/IEC 9636-51991, Information technology - Computer graphics - Interfacing techniques for
dialogues with graphical devices (CGI) - Functional specification - Part 5:
Input and echoing.
ISO/IEC 963696:1991, Information technology - Computer graphics - Interfacing techniques for
dialogues with graphical devices (CGI) - Functional specification - Part 6:
Raster.
Information technology - Computer graphics - Interfacing techniques for
ISO/IEC 9637-2:1992,
dialogues with graphical devices (CGI) - Data stream binding - Part 2: Bi-
nary encoding.
- Procedures for Registration of Graphical Items.
ISO/IEC TR 9973:1988, Information processing
ECMA 96, Graphics Data Syntax for a multiple Workstation Interface.
CEPT, Rev. of TICD 6.1 Videotex Presentation Layer Data Syntax.
2

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@ ISO/IEC
ISO/IEC 9637-lt1994 (E)
CC1 Character Encoding
3 Notational conventions
3 Notational conventions
3.1 ‘I-Bit and ES-Bit code tables
The bits of the bit combinations of the 7-bit code are identified by b7, b6, b5, b4, b3, b2, and bl,
where b7 is the highest-order, or most-significant, bit and bl is the lowest-order, or least-
significant, bit.
The bit combinations may be interpreted to represent integers in the range 0 to 127 in binary nota-
tion by attributing the following weights to the individual bits:
Bit . .
.
b7 b6 b5 b4 b3 b2 bl
Weight: 64 32 16 8 4 2 1
, \
In this part of ISO/IEC 9637 the bit combinations of a 7-bit code are identified by notation of the
form x/y, where x is a number in the range 0 to 7 and y is a number in the range 0 to 15. The
correspondence between the notations of the form x/y and the bit combinations consisting of the
bits b7 to bl is as follows:
- x is the number represented by b7, b6, and b5 where these bits are given the weights 4, 2,
and 1 respectively;
- y is the number represented by b4, b3, b2, and bl where these bits are given the weights 8,
4,2, and 1 respectively.
The notations of the form x/y are the same as those used to identify code table positions, where x is
the column number and y is the row number.
A ‘I-bit code table consists of 128 positions arranged in eight columns and sixteen rows. The col-
umns are numbered 0 to 7 and the rows are numbered 0 to 15. Figure 1 shows a ‘I-bit code table.
An example illustrates the 7-bit code: l/11 refers to the bit combination in column 1, row 11 of the
code table, binary 0011011.
The bits of the bit combinations of the 8-bit code are identified by b8, b7, b6, b5, b4, b3, b2, and bl,
where b8 is the highest-order, or most-significant, bit and bl is the lowest-order, or least-
significant, bit.
The bit combinations may be interpreted to represent integers in the range 0 to 255 in binary nota-
tion by attributing the following weights to the individual bits:
Bit . .
.
b8 b7 b6 b5 b4 b3 b2 bl
128 64 32 16 8 4 2 1
Weight:
Using these weights, the bit combinations of the 8-bit code are interpreted to represent numbers in
the range 0 to 255.
In this part of ISO/IEC 9637 the bit combinations of an 8-bit code are identified by notation of the
3

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ISO/IEC 963701:1994 (E) @ 1s0/IEc
3 Notational conventions CGI Character Encoding
form zlyy, where XX and yy are numbers in the range 00 to 15. The correspondence between the
notations of the form ~lyy and the bit combinations consisting of the bits b8 to bl is as follows:
- xx is the number represented where these bits are given the weights 8
by b8, b7, b6, and b5
9
4,2, and 1 respectively;
- yy is the number represented by b4, b3, b2, and bl where these bits are given the weights 8,
4, 2, and 1 respectively.
The notations of the form xxlyy are the same as those used to identify code table positions, where
XX is the column number and yy is the row number. An 8-bit code table consists of 256 positions
arranged in sixteen columns and sixteen rows. The columns and rows are numbered 00 to 15. Fig-
ure 2 shows an 8-bit code table.
An example illustrates the 8-bit code: 04/01 represents the 8-bit octet 01000001, whereas 4/l repre-
sents the 7-bit octet 1000001.
3.2 Code extension techniques vocabulary
In describing the characters that may occur within string parameters, certain terms imported from
other standards (e.g., IS0 2022) are useful. In the context of the CGI, these terms, and the concepts
to which they refer, apply only within the string parameters of the functions listed in 6.9.4.1.
3.2.1 CO sets
A CO set is a set of 30 control characters represented in a 7-bit code by O/O to l/15, except O/14 and
O/15 which shall be unused, and in an 8-bit code by OO/OO to 01/15, except 00/14 and 00/15 which
shall be unused. CO sets occupy columns 0 and 1 of a 7-bit code table or columns 00 and 01 of an
8-bit code table. The meanings of CO controls within string parameters are specified in 6.9.3.
3.2.2 Cl sets
A Cl set is a set of up to 32 control characters represented by bit combinations 08/00 to 09/15 in an
8-bit code. Cl sets occupy columns 08 and 09 of the 8-bit code table. In a 7-bit code the Cl control
functions are represented by 2-byte escape sequences. This CGI encoding reserves the bit combina-
tions 9/8 and 9/12 (ESC 5/8 and ESC 5/12 in a 7-bit environment, ESC = l/11); these shall not be
part of the content of string parameters. Other Cl control characters from other standards, such as
IS0 6429, may be used within string parameters by agreement between the interchanging parties.
3.2.3 G sets
The G-sets (GO, Gl, G2, G3) are coded character sets of 94 or 96 characters. CHARACTER SET
INDEX designates which character set is to be the GO set. ALTERNATE CHARACTER SET IN-
DEX designates a character set to be used as both the Gl and G2 sets. The G-sets may be “invoked
into” (caused to occupy) columns 2 through 7 of a 7-bit code table, or columns 02 through 07 and 10
through 15 of an 8-bit code table. This encoding of the CGI uses the GO and GlfG2 sets within
string parameters. The G3 set may be used within the string parameters of a conforming CGI data
stream; this requires selection of the extended 7-bit or extended 8-bit mode in the CHARACTER
CODING ANNOUNCER. ISO/IEC 9636 does not provide a diction to explicitly designate the G3
sets; this may be done within a text string in accordance with IS0 2022, or by other means agreed
upon by the interchanging parties.

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0 ISO/IEC
ISO/IEC 9637-1:1994 (E)
CGI Character Encoding
3 Notational conventions
b7 -
0 0
.
b6 - 0 0
Bit
0 1
b5 11111)
0 1
+
0 0 0 0 0
0001 1
OOlOl 2
A G-Set
m The
of 94 or 96
co
.
0111 7
Bit
1000 8 Set
1001 9
Combinations
1010 10
1011 11
1100 12
1101 13
1110 14
1111 15
Figure l- The 7-bit code table.
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
1
00
02100
--I
01
02
03
04
GL-Set GR-Set
co
05
06
of 94 or 96 of 94 or 96
Set
Set
07
08
Bit Combinations Bit Combinations
09
10
11
12
13
14
15
l- 07115 I 15/x
Figure 2 - The &bit code table.
5

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ISO/IEC 9637~ltl994 (E) @ ISO/IEC
4 Overall structure CGI Character Encoding
4 Overall structure
This encoding specifies representations for each of the CGI functions of ISO/IEC 9636 as well as
any associated response. A function representation is the encoded representation of a function with
its In parameters. A response representation is the encoded representation of the Out parameters
of a soliciting function.
4.1 General form of the data stream
All function representations in the data stream are encoded using a uniform scheme. These are rep-
resented as variable length data structures, each consisting of opcode information designating the
particular function representation, and the parameter data (if any).
All response representations in the return data stream are encoded using the same uniform
scheme. These are represented as variable length data structures, each consisting of opcode infor-
mation designating the particular response representation, and its return parameter data.
4.2 Entering and leaving the CGI environment
4.2.1 Implicitly entering the CGI environment
between the interchanging
The CGI coding environment may be entered implicitly, by agreement
services using other coding
parties. This is suitable only if there is not to be any interchange with
techniques.
4.2.2 Designating and invoking the CGI coding environment from
IS02022
For interchange with services using the code extension techniques of IS0 2022, the CGI coding en-
vironment shall be designated and invoked from IS0 2022 environment by the following escape se-
quence:
ESC 215 F
where ESC is the bit combination l/11, and F refers to a bit combination that will be assigned by
the IS0 registration authority for IS0 2375.
The first bit combination occurring after this escape sequence will then represent the opcode of a
CGI function.
After the end of the CGI data (i.e., after the TERMINATE function) the following escape sequence
may be used to return to the IS0 2022 coding environment:
ESC 215 4/O
This not only returns to the IS0 2022 coding environment, but also restores the designation and
invocation of coded character sets to the state that existed prior to entering the CGI coding environ-
ment with the ESC 215 F sequence. (The terms designation and invocation are defined in IS0 2022.)
4.3 Encoding functions
The function descriptions in clause 5 and clause 6, as well as the formal grammars, of ISO/IEC
6

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@ ISO/IEC ISOLIEC 963791:1994 (E)
CGI Character Encoding 4 Overall structure
9636-2, ISO/IEC 9636-3, ISO/IEC 9636-4, ISO/IEC 9636-5, and ISO/IEC 9636-6, provide the basic
syntax needed to encode each CGI function. They contain the function name and the input and out-
put parameters, along with their abstract data types and value ranges. The order in which the pa-
rameters are specified in clause 5 and clause 6 is significant. This is the exact order in which they
will be encoded in a representation.
The character encoding scheme has two basic components: the opcode and the parameter data.
There may be no parameter data, a fixed amount of parameter data or an indefinite amount of pa-
rameter data depending on the function being represented.
CGI functions and their In parameters, if any, are encoded as function representations consisting of
the opcode followed by any In parameter data. Functions with Out parameters are called soliciting
functions. Their Out parameters are considered response data and are encoded in a separate re-
sponse representation, consisting of an opcode followed by the Out parameter data (see 5.4).
representations and the rules for their encoding
The formats of the various function and response
in the character data stream are described below.

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@ 1s0/IEc
ISOLIEC 963791:1994 (E)
CGI Character Encoding
5 Method of encoding opcodes
5 Method of encoding opcodes
Each CGI function representation and response representation is composed of one opcode and pa-
rameters as required. The opcodes are coded as a sequence of bit combinations from columns 2 and
3 of the code chart. The encoding technique supplies:
the basic opcode set;
extension opcode sets.
Parameter bytes are coded in columns 4 to 7 (with the exception of strings, which are otherwise
delimited). This scheme permits an interpreter to skip the parameters of an function representation
which it does not recognize or support. The interpreter can in such circumstances skip bytes until
another opcode is encountered.
5.1 Encoding technique of the basic opcode set
The basic opcode set consists of single-byte and double-byte opcodes. Single-byte opcodes are from
column 2 of the code chart. Bits b4 to bl ar
...