ISO/IEC 8632-2:1992

ISOAEC
INTERNATIONAL
STANDARD 8632-2
Second edition
1992-10-01
------.-.- -------
_ _____ -_ _ -__._._-. --_- - .--- ---------- -----.-. -_ .--.------ - -. _-.--.--.---. .---- -_----- ---_- .---. -__-_.- _.- .---. ---__.--------.----I_---
Information technology - Computer graphics -
Metafile for the storage and transfer of picture
description information -
Part 2:
Character encoding
Technologies de I’hforrnatior~ ---- Infographie -- M&fichier de stockage
et de fr-ansfert des ir~formations de description d’images -
Pat-tie 2: Codaqe des cat-act&-es
\
Reference number
ISCM EC 8632-2: 1992(E)

---------------------- Page: 1 ----------------------
ISO/IEC 8632-2: 1992 (E)
CONTENTS
. . . . . . 1
1 Scope. . . . . . . . . . . . . . . . . . . . . .
. . . . . 2
.
2 Normative references . . . . . . . . . . . . . . . . .
.
. . . . . . . . .
. . . . . . . .
. .
3 Notational conventions
. . . . . * . . . .
. . . . . .
3.1 7-Bit and S-Bit code tables .
. . . . . .
3.2 Code extension techniques vocabulary l . . . . . . . . . .
. . . . . .
3.2.1 CO sets . . . v . . . . . . . . . . . . .
. . . . . .
3.2.2 Cl sets . . . . . . . . . . . . . . . . .
. . .
. . .
3.2.3 G-sets . . . . . . . . . . . . . . . . . .
. . . . . . 7
. . . Q . . . . .
4 Entering and leaving the metafile environment
. . . . . . 7
4.1 Implicitly entering the metafile environment . . . . . . . .
7
. . . . . .
4.2 Designating and invoking the CGM coding environment from IS0 2022
. . . . . . e . . . l
...... . .
5 Method of encoding opcodcs
. . . . . . . . . . . .
.
5.1 Encoding technique of the basic opcode set
. . . . . . . . . . . . .
......
5.2 Extension mechanism
. . . . . . . . . .
....... . . .
5.3 Opcode assignments
. . . . . . 14
. . . . . b .
6 Method of encoding parameters . . . . .
. . . . . 14
. . . . . . . .
6.1 Basic format . . . . . . . . .
. . . . . . . 15
. . . . . .
6.2 Bitstream format . . . . . . . .
. . . . . . . . . 16
. . . .
6.3 Coding integers . . . . . . . .
. . . . . . . * . . . 16
. .
6.4 Coding real numbers . ’ . . . . .
. 0 . . . . . 18
. . . . . .
6.5 Coding VDCs and points . . . . .
. . . . . . 18
. . . . . . .
6.6 Coding point list parameters . . . .
. . . . . . . 18
. . . . . .
6.6.1 Displacement mode . . . . .
. . . . . . . . . 19
. . . .
6.6.2 Incremental mode . . . . .
. . . . . . . . . . 22
. . .
6.6.3 Incremental mode encoding . .
. . . . . . 23
. . . . . . .
6.7 Colour specifiers . . . . . . . .
. . . . . . 24
. * . . . . .
6.8 Colour lists *
. . . . . . 25
. a . . . . .
6.8.1 Normal format*(cdding t&10) .
. . . . . . 25
. . . . . . .
6.8.2 Bitstream format (coding type=l)
. . . . . . . . . 25
. . . .
6.8.3 Runlength format (coding type=2)
. . . . . . . . . . . 25
.
6.8.4 Runlength bitstream format (coding type=3)
. . . . . . . 26
. . . . .
6.8.5 Examples . . . . . . . . . . .
. . . l . . . 27
. . . . . . . . .
6.9 String parameters
. . . . . . . . . 27
. . .
6.9.1 Overall string iaramkter format . . . .
. . . . . 27
6.9.2 Bit combinations permitted within string parameters of text elements
. . . . . 28
6.9.3 CO control within string parameters . . . . . . . . . .
. . . . . 28
6.9.4 Using G-sets in string parameters . . . . . . . . . .
0 lSO/lEC 1992
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from the
publisher.
ISO/IEC Copyriigkt Office l Case postale 56 l CH-1211 Genkve 20 l Switzerland
Printed in Switzerland
11

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ISO/IEC 8632-2: 1992 (E)
Enumerated parameters . . . . . . . . . . . . . . . . . . . . . 29
6.10
. . . . . . . . . 29
Index parameters . . . . . . . . . . . . . .
6.11
. . . . . . . . . . . . . . 29
Data record parameters . . . . . - .
6.12
. . . . . . . . . . . . . . . 29
6.13 Coding VCs and viewport point parameters
. .
. . . . . . . . . . . . . . . 30
6.14 Name parameters . v . . . .
. . . 30
. . . . . . . . . . . . . . .
6.15 Compressed bitstream operands
. . . . 30
. . . . . . . . . . . . . .
6.16 Structured data record operands
. . . 0 . . . l . . . . . 30
6.17 Glyphmapping . . . . . . . . . .
. . . . 31
. . . . . . . . . . . . .
7 Character substitution . . . . . .
. . . . . . . . . . . . . . . . . 33
8 Representation of each element . . .
. . . . . . . . . . . . . . . . . 35
8.1 Delimiter elements . . . . .
BEGINMETAFILE . . . . . . . . . . . . . . . . . . . 35
8.1.1
ENDMETAFILE . . . . . . . . . . . . . . . . . . . . 35
81.2
. . . . 35
8.1.3 BEGINPICTURE . . . . . . . . . . . . . . . .
. . . * . . . 35
8.1.4 BEGIN PICTURE BODY . . . . . . . . . . .
. . . . . . . . . . 35
8.15 ENDPICTURE . l . . . . . . . . .
. . . . . . . . . . . . . 35
8.1.6 BEGINSEGMENT . . . . . . .
. . . . . . . . . . . . . . . . . 36
8.1.7 ENDSEGMENT . . e
BEGINFIGURE . . . . . . . . . . . . . . . . . . . . 36
8.1.8
8.1.9 ENDFIGURE . . . . . . . . . . . . . . . . . . . 0 . 36
8.1.10 BEGIN PROTECTION REGION . . . . . . . . . . . . . . . 36
8.1.11 END PROTECTION REGION . . . . . . . . . . . . . . . . 36
8.1.12 BEGIN COME’OUNDLINE . . . . . . . . . . . . . . . . . 36
. . . . . . . . . . . . . . . 36
8.1.13 END COMPOUNDLINE . . .
BEGIN COMPOUND TEXT PATH . . . . . . . . . . . . . . . 36
8.1.14
END COMPOUND TEXT PATH . . . . . . . . . . . . . . . 36
8.1.15
8.1.16 BEGINTILE ARRAY . . . . . . . . . . . . . . . . . . . 36
ENDTILE ARRAY . . . . . . . . . . . . . . . . . . . 37
8.1.17
8.2 Metafile descriptor elements . . . . . . . . . . . . . . . . . . 38
8.2.1 METAFILE VERSION . . . . . . . . . . . . . . . . 38
. . . . . . . . . . . . 38
8.2.2 METAFILE DESCRIPTION . . . .
. . . . * . . . . . . . . . . 38
8.2.3 VDCTYPE . . . . . .
8.2.4 INTEGER PRECISION . . . . . . . . . . . . . . . . . 38
8.2.5 REAL PRECISION . . . . . . . . . . . . . . . . . . . 38
. . . . . . . . . . . . .
8.2.6 INDEXPRECISION . . . . . 39
8.2.7 COLOUR PRECISION . . . . . . . . . . . . . . . 39
8.2.8 COLOUR INDEX PRECISION . . . . . . . . . . . . . . . 40
8.2.9 MAXIMUM COLOUR INDEX . . . . . . . . . . . . . . . 40
8.2.10 COLOUR VALUE EXTENT . . . . . . . . . . . . . . . . 40
8.2.11 METAFILE ELEMENT LIST . . . . . . . . . . . . . . . 40
8.2.12 METAFILE DEFAULTS REPLACEMENT . . . . . . . . . . . . 41
8.2.13 FONTLIST . . . . . . . . . . . . . . . . . . . . . . 41
8.2.14 CHARACTER SET LIST . . . . . . . . . . . . . . . . . . 41
. . . . . . .
8.2.15 CHARACTER CODING ANNOUNCER . . . . . . 42
. . . . .
8.2.16 NAME PRECISION . . . . . . * . . . . . 42
. .
8.2.17 MAXIMUM VDC EXTENT . . . . . . . . . . 42
. . .
8.2.18 SEGMENT PRIORITY EXTENT. : : : . . . . . . . . . 42
. . .
8.2.19 COLOUR MODEL . . . . . . . . . . . . . . . . . 42
8.2.20 COLOUR CALIBRATION . . . . . . . . . . . . . . . . . 42
. . . 44
8.2.2 1 FONT PROPERTIES . . . . . . . . . . . . . . . .
8.2.22 GLYPH MAPPING . . . . . . . . . . 46
. . . . . . .
8.2.23 SYMBOL LIBRARY LIST’ . . . . . . . . . . . . . . l . . 47
. . .
111

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ISO/IEC8632=2:1992(E)
8.3 Picture descrbtor elements . . . . . . . . . . . . . . . . . . . . 48
................ 48
8.3.1 SCALiNG MODE
............. 48
8.3.2 COLOUR SELECTION-MODE
............. 48
LINE WIDTH SPECIFICATION MODE
8.3.3
............
48
MARKER SIZE SPECIFICATION MODE
8.3.4
.............
48
8.3.5 EDGE WIDTH SPECIFICATION MODE
.....................
49
8.3.6 VDCEXTENT
................. 49
BACKGROUND COLOUR
8.3.7
................... 49
DEVICE VIEWPORT
8.3.8
...........
49
8.3.9 DEVICE VIEWPORT SPECIFICATION MODE
...............
49
8.3.10 DEVICE VIEWPORT MAPPING
.................
50
8.3.11 LINE REPRESENTATION
................
50
8.3.12 MARKER REPRESENTATION
................. 50
8.3.13 TEXT REPRESENTATION
................. 5 1
8.3.14 FILL REPRESENTATION
.................
5 1
8.3.15 EDGE REPRESENTATION
...........
52
8.3.16 INTERIOR STYLE SPECIFICATION MODE
............. 52
8.3.17 LINE AND EDGE TYPE DEFINITION
................ 52
8.3.18 HATCH STYLE DEFINITION
............. 53
8.3.19 GEOMETRIC PATTERN DEFINITION
r.4
....................... 34
8.4 Control elements
................ 54
8.4.1 VDC INTEGER PRECISION
..................
54
8.4.2 VDC REAL PRECISION
..................
55
8.4.3 AUXILIARY COLOUR
.................... 55
8.4.4 TRANSPARENCY
................... 55
8.4.5 CLIPRECTANGLE
.................... 55
8.4.6 CLIP INDICATOR
.................. 55
8.4.7 LINE CLIPPING MODE
................ 56
8.4.8 MARKER CLIPPING MODE
..................
56
8.4.9 EDGE CLIPPING MODE
..................... 56
8.4.10 NEWREGION
................ 56
8.4.11 SAVE PRIMITIVE CONTEXT
............... 56
8.4.12 RESTORE PRIMITIVE CONTEXT
.............. 56
8.4.13 PROTECTION REGION INDICATOR
.............. 57
8.4.14 GENERALIZED TEXT PATH MODE
..................... 57
8.4.15 MITRELIMIT
............... 57
8.4.16 TRANSPARENT CELL COLOUR
................... 58
8.5 Graphical primitive elements
...................... 58
8.5.1 POLYLINE
.................. 58
8.5.2 DISJOINT POLYLINE
.................... 58
8.5.3 POLYMARKER
58
.......................
8.5.4 TEXT.
58
...................
8.5.5 RESTRICTED TEXT
..................... 59
8.5.6 APPENDTEXT
...................... 59
8.5.7 POLYGON
.................... 59
8.5.8 POLYGONSET
..................... 59
8.5.9 CELLARRAY
............. 6 1
8.5.10 GENERALIZED DRAWING PRIMITIVE
..................... 61
8.5.11 RECTANGLE
....................... 61
8.5.12 CIRCLE
................. 61
8.5.13 CIRCULAR ARC 3 POINT
.............. 61
8.5.14 CIRCULAR ARC 3 POINT CLOSE
................. 62
8.515 CIRCULAR ARC CENTRE

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ISO/IEC 8632-2: 1992 (E)
. . . . . . .
8.5.16 CIRCULAR ARC CENTRE CLOSE . . . . . . . 62
. . . . . . . 62
8.5.17 ELLIPSE . . . . . . . . . . . . . . . .
ELLIPTICAL ARC . . . . . . . . . . . . . . . . . . . . 62
8.5.18
ELLIPTICAL ARC CLOSE . . . . . . . . . . . . . . . . 63
8.5.19 .
. . . . . . .
8.5.20 CIRCULAR ARC CENTRE REVERSED . . . . . . 63
.
8.5.21 CONNECTINGEDGE . . . . . . . . . . . . . . . . . 63
. . .
8.5.22 HYPERBOLIC ARC . . . . . . . . . . . . . . . . 63
. . . . .
8.5.23 PARABOLIC ARC . . . . . . . . . . . . . . . 63
. . . . . . . . . . . 64
8.5.24 NON-UNIFORM B-SPLINE . . . . . .
. . . . . .
8.5.25 NON-UNIFORM RATIONAL B-SPLINE . . . . . . . 64
. . . . . . . . . . .
8.5.26 POLYBEZIER . . . . . . . . . . 64
. . . . . . . . . . . . . .
8.5.27 POLYSYMBOL . . . . . . 65
BITONALTILE . . . . . . . . . . . . . . . . . . . . 65
8.5.28
8.5.29 TILE . . . . . . . . . . . . . . . . . . . . . . . . 66
8.6 Attribute elements . . . . . . . . . . . . . . . . . . . . . . 67
8.6.1 LINEBUNDLEINDEX . . . . . . . . . . . . . . . . . . 67
8.6.2 LINETYPE . . . . . . . . . . . . . . . . . . . . . . 67
8.6.3 LINE WIDTH . . . . . . . . . . . . . . . . . . . . . 67
.
8.6.4 LINECOLOUR . . . . . . . . . . . . . . . . . . . 0 67
. . .
8.6.5 MARKER BUNDLE INDEX . . . . . . . . . . . . . . 67
8.6.6 MARKERTYPE . . . . . . . . . . . . . . . . . . . . 67
. . . . . . . .
8.6.7 MARKERSIZE . . . . . . . . . . . . . 68
. . . . . . . . . . . .
8.6.8 MARKERCOLOUR . . . . . . 68
TEXTBUNDLEINDEX . . . . . . . . . . . . . . . . . . 68
8.6.9
8.6.10 TEXTFONTINDEX . . . . . . . . . . . . . . . . . . .
68
8.6.11 TEXTPRECISION . . . . . . . . . . . . . . . . . . . .
68
. . . . . . . . . . . . . 68
8.6.12 CHARACTER EXPANSION FACTOR
8.6.13 CHARACTERSPACING . . . . . . . . . . . . . . . . . . 69
8.6.14 TEXT COLOUR . . . . . . . . . . . . . . . . . . 69
. . .
8.6.15 CHARACTER HEIGHT . . . . . . . . . . . . . 69
. . . . . . . . . . . .
8.6.16 CHARACTERORIENTATiON . . . . 69
TEXT PATH . . . . . . . . . . . . . . . . . . .
8.6.17 69
8.6.18 TEXT ALIGNME& . . o . . . . . . . . . . . . . . 69
8.6.19 CHARACTERSETINDEX . . . . . . . . . . . . . . . . . 70
.
8.6.20 ALTERNATE CHARACTER SET INDEX . . . . . . . . . . . 70
FILLBUNDLEINDEX . . . . . . . . . . . . .
8.6.21 70
8.6.22 . . . . . . . . . . . .
INTERIOR STYLE . 70
8.6.23 FILL COLOUR . . . . . . . . . . . . 71
.........
. . . . . . . . . . .
8.6.24 HATCH INDEX . . 71
. . . . . . . . . . . .
8.6.25 PATTERN INDEX . 71
8.6.26 EDGEBUNDLEINDEX . . . . . . . . . . . . . 71
8.6.27 EDGE TYPE . . . . . . . . . . . . . 71
.
8.6.28 EDGE WIDTH . . . . . . . . . . . . 72
. . . . . . . . . . .
8.6.29 EDGE COLOUR . . 72
8.6.30 EDGE VISIBILITY . . . . . . . . . . . . . . . . 72
. . . . .
8.6.3 1 FILLREFERENCE POiNT . . . . . . . . 72
. . . . . . .
8.6.32 PATTERN TABLE . . . . . . 72
. . . . . . . .
8.6.33 PATTERN SIZE . . . . . 72
. . . . . . . . . . . .
8.6.34 COLOUR TABLE . 73
..... . . . . . . . . . . . .
8.6.35 ASPECTSOURCEFLAGS 73
8.6.36 PICK IDENTIFIER . . . . . . . . . . . . . 74
8.6.37 LINE CAP . . . . . . . . . . . . . 74
8.6.38 LINE JOIN . . . . . . . . . . . . . 74
V

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ISO/IEC 8632-2: 1992 (E)
74
. . . . . . . . .
. . . . . .
.
LINE TYPE CONTINUATION
8.6.39
75
. . . . . . . . .
. . . . . . .
8.6.40 LINE TYPE INITIAL OFFSET
75
. . . . . . . . .
. . . . . . .
8.6.41 TEXT SCORETYPE . . l
. . . . . . . 75
. . . . . . .
. .
8.6.42 RESTRICTED TEXT TYPE .
. 75
. . . . . . . . . . . . . . .
8.6.43 INTERPOLATED INTERIOR
. . . . . . . 76
. * . . . * . . .
8.6.44 EDGECAP . . . . . .
. . . . . . . 76
. . . . . . . . .
8.6.45 EDGEJOIN . . . . . .
. . . . . . . . . 76
. . . . . . .
EDGE TYPE CONTINUATION
8.6.46
l . . . . . 77
. . . . . . . . . .
8.6.47 EDGE TYPE INITIAL OFFSET
* . . . . . . . . 77
. . . . . . .
8.6.48 SYMBOL LIBRARY INDEX
. . . . . . . . . 77
. . . . . . . .
8.6.49 SYMBOLCOLOUR l .
. . . . . . . . . . . . . . 77
. . .
8.6.50 SYMBOLSIZE . . . .
77
. . . . . . . . . . . . . . . .
SYMBOL ORIENTATION .
8.6.5 1
. * 78
. . . . . . . . . . . . . .
.
8.7 Escape elements . . . . . .
78
. . . . . . . . . . . . . . . .
8.7.1 ESCAPE . . e . . . .
. 78
. . . . . . . . . . . . . . . .
8.7.2 DOMAINRING . . .
. * . . . 79
. . . . . . . . . . . .
8.8 External elements . . . . .
. . . . . . . 79
. . . . . . . . . .
8.8.1 MESSAGE . . . . .
. . . . . . . . . . . . . 79
. . . .
8.8.2 APPLICATION DATA .
. . . * . . . . . 80
. . . . . . 0 .
8.9 Segment elements . . . . .
. . . . . . . . . . . . . 80
. . . .
8.9.1 COPY SEGMENT . . .
. . . . . . . . . . . . . 80
. . . .
8.9.2 INHERITANCE FILTER .
. . . . . . . . . . . . . . . 82
8.9.3 CLIP INHERITANCE . . . .
. . . . . . . . . . . . . . . 82
8.9.4 SEGMENT TRANSFORMATION
. . . .
. . . . . . . . . . . 82
8.9.5 SEGMENT HIGHLIGHTING
. . . . . . . . . . . . . . . 83
8.9.6 SEGMENT DISPLAY PRIORITY*
. . . . . . . . . . . . . . . . 83
8.9.7 SEGMENT PICK PRIORITY
. . . . . . . . . . . . . . 84
9 Defaults . . . . . . . . . . . . .
. 85
10 Conformance . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . l . 86
A Formal grammar . . . . . . . . .
vi

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ISO/IEC 8632-2: 1992 (E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the 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, ISOIIEC 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 ISOIIEC 8632-2 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information
technology.
This second edition cancels and replaces the first edition (IS0 8632-2: 1987), which has been technically revised.
ISOIIEC 8632 consists of the following parts, under the general title Information technology - Computer
graphics -Metafile for the storage and transfer of picture description information :
Part I : Functional specijkation
Part 2: Character encoding
Part 3: Binary encoding
Part 4: Clear text encoding
Annex A forms an integral part of this part of ISO/IEC 8632.
vii

---------------------- Page: 7 ----------------------
ISO/IEC 8632-2: 1992 (E)
Introduction
0.1 Purpose of the character encoding
The Character Encoding of the Computer Graphics Metafile (CGM) provides a representation of the
Metafile syntax intended for situations in which it is important to minimize the size of the metafile or
transmit the metafile 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 8632-3 may be more appropriate. If human readability is the most
important criterion, an encoding such as the Clear Text Encoding in ISO/IEC 8632-4 may be more
appropriate.
0.2 Objectives
This encoding was designed with the following objectives:
regular syntax: All elements of the metafile should be encoded in a uniform way so that parsing
a>
the metafile is simple;
compactness: The encoding should provide a highly compact metafile, suitable for systems with
b)
restricted storage capacity or transfer bandwidth;
extensibility: the encoding should allow for future extensions;
C>
transportability: the encoding should be suitable for use with transport mechanisms designed for
d)
character-oriented data based on a standard national character set derived from ISO/IEC 646.
0.3 Metafile characteristics
Each CGM command follows a simple regular syntax. Thus, new commands can be added in a future revi-
sion of ISO/IEC 8632 such that existing CGM interpreters can recognize (and ignore) the new commands
Also, new operands can be added to existing commands in the future revision of the standard such tha
existing CGM interpreters can recognize (and ignore) the additional operands.
Each CGM operand follows a simple regular syntax. Operands are variable in length. This permits smal
values to be represented by the smallest number of bytes.
. . .
Vlll

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ISO/IEC 8632-2: 1992 (E)
Introduction
Metafile characteristics
A certain range of operand values of standard commands have been reserved for private use; the remaining
range is either standardized or reserved for future standardization.
0.4 Relationship to other International Standards
The Character Encoding has been developed in collaboration with the IS0 subcommittee responsible for
character sets and coding, ECMA, and CEPT. The encoding 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 8632 follows the rules of ISO/IEC 646 and IS0
2022.
For certain elements, the CGM defines value ranges as being reserved for registration. The values and t.he.ir
meanings will be defined using the established procedures (see ISO/IEC 8632-1, sub-clause 4.12.)
1x

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INTERNATIONAL STANDARD ISO/IEC 8632-2: 1992 (E)
Information technology - Computer graphics - Metafile for
the storage and transfer of picture description information -
Part 2 :
Character encoding
1 Scope
This part of ISO/IEC 8632 specifies a character encoding of the Computer Graphics Metafile. For each of
the elements specified in ISO/IEC 8632-1 an encoding is specified.
This encoding of the Computer Graphics Metafile provides a highly compact representation of the metafile,
suitable for applications that require the metafile to be of minimum size and suitable for transmission with
character-oriented transmission services.

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ISO/IEC 8632-2: 1992 (E)
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of
this part of ISO/IEC 8632. At the time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this part of ISO/IEC 8632 are encouraged to investi-
gate the possibility of applying the most recent editions of the standards listed below. Members of IEC and
IS0 maintain registers of currently valid International Standards.
IS0 7-bit coded character set for information interchange.
ISOLIEC 646: 199 1, Information technology -
IS0 2022: 1986, Information processing - IS0 7-bit and S-bit coded character sets - Code extension techniques.
Procedure for registration of escape sequences.
IS0 2375: 1985, Data processing -
Control functions for 7-bit and &bit coded character sets.
IS0 6429: 1988, Information processing -
ECMA 96, Graphics Data Syntax for a multiple Workstation Integace.
CEPT, Revision of T/CD 6.1 Videotex Presentation Layer Data Syntax.

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ISO/IEC 8632-2: 1992 (E)
3 Notational conventions
3.1 7,Bit and &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 notation by
attributing the following weights to the individual bits:
.
Bit .
b6 b5 b4 b3 b2 bl
b7
.
. 64 32 16 8 4 2 1
Weight .
In this part of ISO/IEC 8632, the bit combinations 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 nota-
tions of the form xl/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 7-bit code table consists of 128 positions arranged in eight columns and sixteen rows. The columns are
numbered 0 to 7 and the rows are numbered 0 to 15. Figure 1 shows a 7-bit code table.
“l/l 1” refers to the bit combination in column 1, row 11 of the code
An example illustrates the 7-bit 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 notation 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 8632, the bit combinations are identified by notation of the form xxIyy, where XX and
yy are numbers in the range 00 to 15. The correspondence between the notations of the form xx/yy and the
bit combinations consisting of the bits b8 to bl is as follows:
- xx is the number represented by b8, b7, b6, and b5 where these bits are given the weights 8,4, 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 ;“IxIyy 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. Figure 2 shows an 8-bit code
3

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ISOlIEC 8632-2: 1992 (E)
Notational conventions
7-Bit and &Bit code tables
table.
An example illustrates the 8-bit code: 04/01 represents the 8-bit byte 01000001, whereas 4/l represents the
7-bit byte 1000001.
3.2 Code extension techniques vocabulary
certain terms imported from other
In describing the characters that may occur within string parameters,
standards (e.g., IS0 2022) are useful. In the context of the CGM, these terms, and the concepts to which
they refer, apply only within the string parameters of the TEXT, APPEND TEXT, and RESTRICTED
TEXT metafile elements.
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/l5
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 described 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 OS/O0 to 09/15 in an 8-bit
In a 7-bit code the Cl control functions
code. Cl sets occupy columns 08 and 09 of the 8-bit code table.
are represented by 2-byte escape sequences. This CGM encoding reserves the bit combinations 9/8 and
9/12 (ESC 5/8 and ESC 5/12 in a 7-bit environment, ESC = l/l 1); 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 INDEX 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 CGM uses the GO and Gl/G2 sets within string parameters. The G3 set may be
used within the string parameters of conforming metafiles; this requires selection of the extended 7-bit or
extended 8-bit mode in the CHARAmR CODING ANNOUNCER. The CGM does not provide an ele-
ment 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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ISO/IEC 8632-2: 1992 (E)
Code extension techniques vocabulary
Notational conventions
A G-SET OF
94 OR 96
BIT COMBINATIONS
Figure l- The 7-bit code table

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ISO/IEC 8632-2: 1992 (E)
Code extension techniques vocabulary Notational conventions
02 03 04 05 06 07
00 01 08 09
0
02/q
1
2
3
4
5
6
"GR" SET C
co "GL" SET OF
7 Cl
94 OR 96
94 OR 96
SET SET
8
BIT COMBINAT ONS
BIT COMBINATIONS
9
10
11
12
13
14
15
IO?. 15 I15/ 15
Figure 2 - The S-bit code table

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ISO/IEC 8632-2: 1992 (E)
4 Entering and leaving the metafile environment
4.1 Implicitly entering the metafile environment
The CGM coding environment may be entered implicitly, by agreement between the interchanging parties.
This is suitable only if there is not to be any interchange with services using other coding techniques.
4.2 Designating and invoking the CGM coding environment from IS0 2022
For interchange with services using the code extension techniques of IS0 2022, the CGM coding environ-
ment shall be designated and invoked from IS0 2022 environment by the following escape sequence:
ESC 215 F
where ESC is the bit combination l/l 1, and F refers to a bit combination that will be assigned by the IS0
Registration Authority for IS0 2375.
The first bit combination occuring after this escape sequence will then represent the opcode of a CGM
metafile element.
After the end of one or more metafiles (i.e., after the END METAFILE clement) or between pictures (i.e.,
after the END PICTURE element), 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 CGM coding environment with the ESC
2/5 F sequence. (The terms “designation” and “invocation” arc defined in IS0 2022.)

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ISO/IEC 8632-2: 1992 (E)
5 Method of encoding opcodes
Each metafile element is composed of one opcode and parameters as required. The opcodcs are coded as a
sequence of bit combinations from columns 2 and 3 of the code chart. The
...