ISO/TR 12033:2009

TECHNICAL ISO/TR
REPORT 12033
First edition
2009-12-01
Document management — Electronic
imaging — Guidance for the selection of
document image compression methods
Gestion de documents — Imagerie électronique — Directives pour le
choix des méthodes de compression d'image

Reference number
©
ISO 2009
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ii © ISO 2009 – All rights reserved

Contents
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 General .3
5 Type of document and digitization parameters .4
5.1 General .4
5.2 Type of documents.4
5.3 Document classification and digitization.4
6 Compression methods and standards.6
6.1 LZW compression (Lempel Ziv Welch) .6
6.2 RLE compression (run-length encoding).6
6.3 ITU-T algorithms.6
6.4 JBIG compression.8
6.5 JBIG2 compression.8
6.6 Discrete cosine transform (DCT) .8
6.7 Fractal compression .8
6.8 Wavelet compression.9
6.9 JPEG compression.9
6.10 JPEG 2000 .10
7 Selection of compression parameters .12
7.1 Pertinence of compression .12
7.2 Selection of a compression method.12
7.3 Adjusting JPEG compression.13
8 Final considerations for the selection of a compression method .14
Bibliography.15

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 12033 was prepared by Technical Committee ISO/TC 171, Document management applications,
Subcommittee SC 2, Application issues.
This first edition of ISO/TR 12033 cancels and replaces ISO/TS 12033:2001, which has been technically
revised.
iv © ISO 2009 – All rights reserved

Introduction
With respect to the rapid increase of applications using digitization techniques, the role of compression
methods has become a factor of growing importance for the management of the volumes of stored data.
The effects of the available compression methods vary greatly, depending on the source documents. For
example, an electronic image management (EIM) system configured for scanning and storing continuous tone
images will have different image compression requirements as compared to an application involving only text.
Practical methods for analysing user requirements for image compression in order to select accurate and
optimal image compression schemes are complex. This Technical Report was issued in order to guide users
and system developers in their selection of these methods.

TECHNICAL REPORT ISO/TR 12033:2009(E)

Document management — Electronic imaging — Guidance for
the selection of document image compression methods
1 Scope
This Technical Report gives information to enable a user or electronic image management (EIM) integrator to
make an informed decision on selecting compression methods for digital images of business documents. It
provides technical guidance to analyse the type of documents and which compression methods are most
suitable for particular documents in order to optimize their storage and use.
For the user, this Technical Report provides information on image compression methods incorporated in
hardware or software in order to help the user during the selection of equipment in which the methods are
embedded.
For the equipment or software designer, this Technical Report provides planning information.
This Technical Report is applicable only to still images in bit map mode. It only takes into account
compression algorithms based on well-tested mathematical work.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 12651:1999, Electronic imaging — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12651 and the following apply.
3.1
compression
process of removing redundancies in digital data to reduce the amount that should be stored or transmitted
NOTE Lossless compression removes only enough redundancy so that the original data can be recreated exactly as
it was. Lossy compression sacrifices additional data to achieve greater compression. This is typically useful for greyscale
or colour image compression, where details that are not perceptible, or are minimally perceptible, to the human eye can be
eliminated, normally with a dramatic increase in compression. It is advisable that lossy compression not be used for
documents containing textual information and not be used for long term archival of any type of documents.
3.2
resolution
number of pixels per unit of length
3.3
dots per inch
dpi
number of dots that a scanner (printer) can scan (print) per inch both horizontally or vertically
3.4
brightness
visual sensation that enables an observer to detect luminance
3.5
contrast
ratio of on pixel brightness to off pixel brightness
3.6
bit level
number of bits used to define a pixel
3.7
luminance
Y
luminous flux emitted from a surface
NOTE The former term was photometric brightness.
3.8
chrominance
Cr
Cb
colour portion of the video signal including hue and saturation but not brightness
NOTE Low chroma means the colour picture looks pale or washed out; high chroma means intense colour; black,
grey and white have a chrominance equal to zero.
3.9
ITU-T Group 3 and Group 4
compression algorithms standards defined by the ITU-T in Recommendations T.4 and T.6
3.10
Joint Photographic Experts Group
JPEG
name of the committee that developed the ISO/IEC 10918 series which shares the same popular name
NOTE The “J” refers to the joint development with the ITU-T.
3.11
Comité Consultatif International Télégraphique et Téléphonique
former name of the International Telecommunication Union (ITU) standardization body
3.12
compression ratio
relationship of the total bits used to represent the original to the total number of encoded bits
3.13
Joint Bi-level Image Experts Group
JBIG
name of the sub committee that developed ISO/IEC 11544
NOTE The joint committee is with ITU-T. JBIG and JPEG are managed by ISO/IEC JTC1/SC 29/Working Group 1.
2 © ISO 2009 – All rights reserved

4 General
In a document imaging system, users are concerned about the quality of archived images, for two reasons:
a) it can affect the imaging system's future in the medium or even long-term;
b) it is necessary to choose the imaging tools based on an evolving technology.
The digitization process, which by nature transforms an image conveying comprehensible information into a
dematerialized one, changes the observer's perception of that image. The observer may consider the image
as being improved, though more frequently he considers it degraded. In fact, images undergo a number of
successive transformations at different points during the digitization process. At each of these stages,
attempts are made to keep the image within acceptable legibility limits, but also to restrict its size to within
acceptable economic limits.
The specific role of one of the digitization stages ― compression ― is to reduce the size of the image. Some
compression methods are reversible in that the decompression algorithm restores the initial digital information.
These methods are lossless and have no impact on the quality of the image as it is perceived by the human
eye. Other methods are lossy, and may cause degradation perceptible to the eye. By adjusting certain
parameters, the user can bring a lossy method within acceptable limits; because the acceptance of a lossy
method is a subjective judgement. Any image or document, on which a computerized treatment may be
applied, should not be compressed with such a method. This is one of the major reasons not to use lossy
compression for long-term archiving, as future usage of the image or document is unknown.
While numerous compression methods are described in technical literature, few are stable according to
industrial standards. These are based on a limited number of principles:
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