ISO/IEC 20071-11:2019
(Main)Information technology — User interface component accessibility — Part 11: Guidance on text alternatives for images
Information technology — User interface component accessibility — Part 11: Guidance on text alternatives for images
This document gives guidance on how to create text alternatives and what information to put in text alternatives. This document applies to all static images that are used in any type of electronic document. It also applies to individual images within a slide show. This document does not apply to moving images (e.g. movies). NOTE 1 While text alternatives can be implemented via various mechanisms in various types of electronic documents, the contents of this document are not dependent on the choice of implementation mechanism or of electronic document type. NOTE 2 Guidance on making moving images accessible is contained in ISO/IEC TS 20071-21, ISO/IEC 20071-23 and ISO/IEC 20071-25.
Technologies de l'information — Accessibilité du composant interface utilisateur — Partie 11: Lignes directrices pour les textes alternatifs pour images
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Standards Content (Sample)
INTERNATIONAL ISO/IEC
STANDARD 20071-11
First edition
2019-12
Information technology — User
interface component accessibility —
Part 11:
Guidance on text alternatives for
images
Technologies de l'information — Accessibilité du composant interface
utilisateur —
Partie 11: Lignes directrices pour les textes alternatifs pour images
Reference number
ISO/IEC 20071-11:2019(E)
©
ISO/IEC 2019
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ISO/IEC 20071-11:2019(E)
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ISO/IEC 20071-11:2019(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Text alternatives and related definitions . 1
3.2 Image and related definitions . 2
3.3 Image types and related definitions . 3
3.4 Image content and related definitions. 3
3.5 Information relationship definitions . 4
3.6 Information type definitions . 4
3.7 Importance and related definitions . 5
4 Text alternatives for images . 6
4.1 Uses of text alternatives . 6
4.2 Presenting text alternatives . 7
4.2.1 General. 7
4.2.2 Text alternatives within the main body of text . 7
4.2.3 Primary alternative text . . 7
4.2.4 Secondary alternative text . 8
5 Procedure for creating text alternatives . 8
6 Identifying the types of image . 9
6.1 General . 9
6.2 Drawings . 9
6.3 Photographs .10
6.4 Diagrams .10
6.5 Maps .10
6.6 Computer-generated illustrations .11
6.7 Composite images .11
6.8 Identifying image type in text alternatives .11
6.8.1 Identifying the image type of single images .11
6.8.2 Identifying image type of composite images with separately addressable
components .11
7 Identifying the purpose of the image .12
7.1 Introduction to purposes .12
7.2 Informative purposes .12
7.3 Control purposes .13
7.4 Decorative purposes.13
7.4.1 Decorative images that convey affective information .13
7.4.2 Decorative images with minimal information value .13
7.5 Formatting purposes .14
7.6 Identifying purpose in text alternatives .14
7.6.1 Describing the purpose .14
7.6.2 Stating the purpose briefly .14
7.6.3 Avoiding redundancy with captions .15
7.6.4 Considering the context of use.15
7.6.5 Considering both objective and subjective purposes .15
7.6.6 Text alternatives for images used for formatting purposes .15
7.6.7 Further information for images used for informative purposes .15
7.6.8 Further information for images used for control purposes .16
8 Identifying the image components .16
8.1 Images and image components .16
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ISO/IEC 20071-11:2019(E)
8.2 Text components .16
8.3 Uniquely identifying image components .16
8.4 Structuring information about images and their components .17
8.5 Dealing with image complexity .18
8.5.1 Use of image components .18
8.5.2 Textual information in images .18
8.5.3 Information about whole images .19
8.5.4 Information about image components .19
9 Identifying the information (content) presented by the image .19
9.1 Content of an image or its components .19
9.2 Subjective content .19
9.3 Objective content .20
9.4 Relationship content .21
9.4.1 Relationships .21
9.4.2 Actions .21
9.4.3 Logical relationships .22
9.4.4 Temporal relationships .22
9.4.5 Physical (spatial) relationships .23
9.5 Interaction content .24
9.6 Analysing the information presented by an image .24
10 Evaluating the importance of the information about the image .25
10.1 Importance is context dependent .25
10.2 Importance .25
10.2.1 Levels of importance .25
10.2.2 Essential information.25
10.2.3 Significant information . .26
10.2.4 Helpful information .26
10.2.5 Not important information .27
10.3 Textual content in images .27
10.4 Using importance to allocate information to text alternatives .28
10.4.1 Including subjective information in text alternatives .28
10.4.2 Including objective information in text alternatives .28
10.4.3 Including relationship information in text alternatives .28
10.4.4 Including information on associated activities in text alternatives .28
10.4.5 Dealing with large amounts of essential information .28
10.4.6 Placing text alternatives in the main body of text .28
10.4.7 Handling conflicting information .29
11 Compose the text alternatives .29
11.1 Composition .29
11.2 Organizing the information .29
11.2.1 Eliminating duplications .29
11.2.2 Fitting into the context of use of the image .30
11.2.3 Independence of importance from order .30
11.3 Wording text alternatives .30
11.3.1 Flow with the document content .30
11.3.2 Style .30
11.3.3 Conciseness and readability .31
11.4 Creating text alternatives .31
12 Evaluate the text alternative .31
12.1 The range of evaluation issues .31
12.2 The range of evaluation methods and testers .31
Annex A (informative) Further elaboration of objective content of images .33
Annex B (informative) Further considerations for particular types of images .37
Bibliography .41
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ISO/IEC 20071-11:2019(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
are members of ISO 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. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
list of patent declarations received (see http:// patents .iec .ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 35, User interfaces.
This first edition of ISO/IEC 20071-11 as an International Standard cancels and replaces the Technical
Specification (ISO/IEC TS 20071-11:2012), which has been technically revised.
The main changes compared to the Technical Specification are as follows:
— a major restructuring and simplification of the requirements;
— the addition of image type specific information in annexes.
A list of all parts in the ISO/IEC 20071 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO/IEC 20071-11:2019(E)
Introduction
The saying that "A picture is worth a thousand words" recognizes that images can present a wealth
of information. It is important that alternative textual descriptions or representations present a
comprehensive account of the purpose and content of images to people unable to see or interpret them.
Text alternatives help people who cannot see the images to understand what the image is of or the
purpose it serves by providing the same information in textual form. Text alternatives can be useful
to those with visual impairments, those who turned images off in order to improve webpage loading
speeds, and those who cannot understand the image being displayed. They can also aid search engines
in finding images. This document provides guidance for user interface, web and document developers
to help them create informative descriptions for various types of illustrations.
While some sources of guidance advocate that text alternatives be kept short, it is important that they
provide an equitable alternative to the image. ISO/IEC Guide 71 states "A system provides equitable
use if it allows diverse users to accomplish tasks in an identical manner whenever possible or in an
equivalent manner when an identical manner is not possible". This document provides guidance
intended to help developers create equitable text alternatives.
The guidance contained in this document is intended to be used by the person who creates content and/
or text alternatives to be placed in an electronic document. There is no expectation that this person will
have any additional expertise beyond understanding the contents of the document and why an image
was chosen to be placed within the document.
While the main intent of the guidance within this document is the creation of text alternatives, the
information identified in this guidance could be placed in the main document text, reducing the length
of the resulting text alternatives. However, placing information in the main document text does not
fully replace the function of having some text alternatives for each image.
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INTERNATIONAL STANDARD ISO/IEC 20071-11:2019(E)
Information technology — User interface component
accessibility —
Part 11:
Guidance on text alternatives for images
1 Scope
This document gives guidance on how to create text alternatives and what information to put in text
alternatives.
This document applies to all static images that are used in any type of electronic document. It also
applies to individual images within a slide show.
This document does not apply to moving images (e.g. movies).
NOTE 1 While text alternatives can be implemented via various mechanisms in various types of electronic
documents, the contents of this document are not dependent on the choice of implementation mechanism or of
electronic document type.
NOTE 2 Guidance on making moving images accessible is contained in ISO/IEC TS 20071-21, ISO/IEC 20071-23
and ISO/IEC 20071-25.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 Text alternatives and related definitions
3.1.1
text alternative
alternative text
textual description or representation of an image
Note 1 to entry: By storing this description or representation in text format, it is able to be rendered in any
available modality.
Note 2 to entry: The main audience of text alternatives are the users of screen reading features.
Note 3 to entry: Text alternatives are often provided to screen reader users in the form of primary and secondary
alternative texts of an image.
Note 4 to entry: Generally, "text alternative" is used to refer to any text alternative, while "alternative text" is
used to refer to text alternatives for images that are contained in attributes of an image.
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ISO/IEC 20071-11:2019(E)
3.1.2
primary alternative text
main text alternative provided to users of screen readers
Note 1 to entry: Different technologies and platforms provide various mechanisms for containing and presenting
primary alternative text.
EXAMPLE 1 In HTML 5.2 and EPUB, primary alternative text is provided in the “alt” attribute of the img tag.
EXAMPLE 2 In PDF, primary alternative text is provided through the /Alt entry in a structure element’s
dictionary.
3.1.3
secondary alternative text
additional text alternative provided to users of screen readers beyond primary alternative text
Note 1 to entry: Different technologies and platforms provide various mechanisms for containing and presenting
secondary alternative text.
EXAMPLE 1 In HTML5.2, secondary alternative text is provided in the “longdesc” attribute of the img tag.
EXAMPLE 2 In EPUB, secondary alternative text is provided through the “role” attribute.
3.1.4
main body of text
textual content of a document that is always presented to the users
3.2 Image and related definitions
3.2.1
image
graphical content intended to be presented visually
Note 1 to entry: This includes graphics that are encoded in any electronic format, including, but not limited
to, formats that are comprised of individual pixels (e.g. those produced by paint programs or by photographic
means) and formats that comprised of formulas (e.g. those produced as scalable vector drawings).
3.2.2
static image
image where the set of image components and their relationships to one another do not change over time
Note 1 to entry: This includes images where the content/representation of individual image components can
change over time, e.g. indicators where the value they are indicating changes in real time.
Note 2 to entry: The concept of static image is used for all images that are not slide shows or moving images.
Note 3 to entry: This use of static image is similar to the ISO/IEC 13249-5 use of "still image". However, it differs
in that a static image can have moving components. ISO/IEC 13249-5 states "A still image user-defined type is
generic to image handling. It addresses the need to store, manage, and retrieve information based on aspects of
inherent image characteristics such as height, width, and format and based on image features such as average
color, color histogram, positional color, and texture. It also addresses the need to employ manipulation such as
rotation, scaling as well as similarity assessment".
3.2.3
slide show
set of images that replace one another periodically
Note 1 to entry: The replacement of one static image by another static image can be controlled automatically by
the system (in which case the timing for each image is usually predetermined) or manually by the user (where
the timing for each image is determined on a case by case basis).
Note 2 to entry: Slide shows are usually composed of static images but can include short movies. The interval
between static images in a slide show are considered longer than in a movie, such that the motion being portrayed
by the slide show would appear stagger
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