INTERNATIONAL TELECOMMUNICATION UNION
CCITT T.81
THE INTERNATIONAL (09/92)
TELEGRAPH AND TELEPHONE
CONSULTATIVE COMMITTEE
TERMINAL EQUIPMENT AND PROTOCOLS
FOR TELEMATIC SERVICES
INFORMATION TECHNOLOGY –
DIGITAL COMPRESSION AND CODING
OF CONTINUOUS-TONE STILL IMAGES –
REQUIREMENTS AND GUIDELINES
Recommendation T.81
Foreword
ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of
telecommunications. The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent
organ of the ITU. Some 166 member countries, 68 telecom operating entities, 163 scientific and industrial organizations
and 39 international organizations participate in CCITT which is the body which sets world telecommunications
standards (Recommendations).
The approval of Recommendations by the members of CCITT is covered by the procedure laid down in CCITT Resolution
No. 2 (Melbourne, 1988). In addition, the Plenary Assembly of CCITT, which meets every four years, approves
Recommendations submitted to it and establishes the study programme for the following period.
In some areas of information technology, which fall within CCITT’s purview, the necessary standards are prepared on a
collaborative basis with ISO and IEC. The text of CCITT Recommendation T.81 was approved on 18th September 1992.
The identical text is also published as ISO/IEC International Standard 10918-1.
___________________
CCITT NOTE
In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication
administration and a recognized private operating agency.
ITU 1993
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 ITU.
Contents
Page
Introduction.............................................................................................................................................................. iii
1 Scope ............................................................................................................................................................ 1
2 Normative references..................................................................................................................................... 1
3 Definitions, abbreviations and symbols......................................................................................................... 1
4 General ......................................................................................................................................................... 12
5 Interchange format requirements................................................................................................................... 23
6 Encoder requirements ................................................................................................................................... 23
7 Decoder requirements ................................................................................................................................... 23
Annex A – Mathematical definitions........................................................................................................................ 24
Annex B – Compressed data formats........................................................................................................................ 31
Annex C – Huffman table specification.................................................................................................................... 50
Annex D – Arithmetic coding.................................................................................................................................. 54
Annex E – Encoder and decoder control procedures................................................................................................ 77
Annex F – Sequential DCT-based mode of operation............................................................................................... 87
Annex G – Progressive DCT-based mode of operation............................................................................................. 119
Annex H – Lossless mode of operation .................................................................................................................... 132
Annex J – Hierarchical mode of operation................................................................................................................ 137
Annex K – Examples and guidelines........................................................................................................................ 143
Annex L – Patents.................................................................................................................................................... 179
Annex M – Bibliography.......................................................................................................................................... 181
CCITT Rec. T.81 (1992 E) i
Introduction
This CCITT Recommendation | ISO/IEC International Standard was prepared by CCITT Study Group VIII and the Joint
Photographic Experts Group (JPEG) of ISO/IEC JTC 1/SC 29/WG 10. This Experts Group was formed in 1986 to
establish a standard for the sequential progressive encoding of continuous tone grayscale and colour images.
Digital Compression and Coding of Continuous-tone Still images, is published in two parts:
– Requirements and guidelines;
– Compliance testing.
This part, Part 1, sets out requirements and implementation guidelines for continuous-tone still image encoding and
decoding processes, and for the coded representation of compressed image data for interchange between applications.
These processes and representations are intended to be generic, that is, to be applicable to a broad range of applications for
colour and grayscale still images within communications and computer systems. Part 2, sets out tests for determining
whether implementations comply with the requirments for the various encoding and decoding processes specified in Part
1.
The user’s attention is called to the possibility that – for some of the coding processes specified herein – compliance with
this Recommendation | International Standard may require use of an invention covered by patent rights. See Annex L for
further information.
The requirements which these processes must satisfy to be useful for specific image communications applications such as
facsimile, Videotex and audiographic conferencing are defined in CCITT Recommendation T.80. The intent is that the
generic processes of Recommendation T.80 will be incorporated into the various CCITT Recommendations for terminal
equipment for these applications.
In addition to the applications addressed by the CCITT and ISO/IEC, the JPEG committee has developped a compression
standard to meet the needs of other applications as well, including desktop publishing, graphic arts, medical imaging and
scientific imaging.
Annexes A, B, C, D, E, F, G, H and J are normative, and thus form an integral part of this Specification. Annexes K, L
and M are informative and thus do not form an integral part of this Specification.
This Specification aims to follow the guidelines of CCITT and ISO/IEC JTC 1 on Rules for presentation of CCITT |
ISO/IEC common text.
ISO/IEC 10918-1 : 1993(E)
INTERNATIONAL STANDARD
ISO/IEC 10918-1 : 1993(E)
CCITT Rec. T.81 (1992 E)
CCITT RECOMMENDATION
INFORMATION TECHNOLOGY – DIGITAL COMPRESSION
AND CODING OF CONTINUOUS-TONE STILL IMAGES –
REQUIREMENTS AND GUIDELINES
1 Scope
This CCITT Recommendation | International Standard is applicable to continuous-tone – grayscale or colour – digital still
image data. It is applicable to a wide range of applications which require use of compressed images. It is not applicable to
bi-level image data.
This Specification
– specifies processes for converting source image data to compressed image data;
– specifies processes for converting compressed image data to reconstructed image data;
– gives guidance on how to implement these processes in practice;
– specifies coded representations for compressed image data.
NOTE – This Specification does not specify a complete coded image representation. Such representations may include
certain parameters, such as aspect ratio, component sample registration, and colour space designation, which are application-
dependent.
2 Normative references
The following CCITT Recommendations and International Standards contain provisions which, through reference in this
text, constitute provisions of this CCITT Recommendation | International Standard. At the time of publication, the
editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agreements
based on this CCITT Recommendation | International Standard are encouraged to investigate the possibility of applying
the most recent edition of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers
of currently valid International Standards. The CCITT Secretariat maintains a list of currently valid CCITT
Recommendations.
– CCITT Recommendation T.80 (1992), Common components for image compression and communication –
Basic principles.
3 Definitions, abbreviations and symbols
3.1 Definitions and abbreviations
For the purposes of this Specification, the following definitions apply.
3.1.1 abbreviated format: A representation of compressed image data which is missing some or all of the table
specifications required for decoding, or a representation of table-specification data without frame headers, scan headers,
and entropy-coded segments.
3.1.2 AC coefficient: Any DCT coefficient for which the frequency is not zero in at least one dimension.
3.1.3 (adaptive) (binary) arithmetic decoding: An entropy decoding procedure which recovers the sequence of
symbols from the sequence of bits produced by the arithmetic encoder.
3.1.4 (adaptive) (binary) arithmetic encoding: An entropy encoding procedure which codes by means of a recursive
subdivision of the probability of the sequence of symbols coded up to that point.
3.1.5 application environment: The standards for data representation, communication, or storage which have been
established for a particular application.
CCITT Rec. T.81 (1992 E) 1