Screen reader
Encyclopedia
A screen reader is a software application
that attempts to identify and interpret what is being displayed on the screen (or, more accurately, sent to standard output
, whether a video monitor is present or not). This interpretation is then re-presented to the user with text-to-speech, sound icons, or a Braille output device
. Screen readers are a form of assistive technology
(AT) potentially useful to people who are blind
, visually impaired
, illiterate or learning disabled
, often in combination with other AT, such as screen magnifier
s.
A person's choice of screen reader is dictated by many factors, including platform, cost (even to upgrade a screen reader can cost hundreds of U.S. dollars), and the role of organizations like charities, schools, and employers. Screen reader choice is contentious: differing priorities and strong preferences are common.
Microsoft Windows
operating systems have included the Microsoft Narrator
light-duty screen reader since Windows 2000
. Apple Inc. Mac OS X
includes VoiceOver
, a feature-rich screen reader. The console-based Oralux
Linux
distribution ships with three screen-reading environments: Emacspeak
, Yasr and Speakup. The open source GNOME
desktop environment long included Gnopernicus
and now includes Orca
.
There are also open source
screen readers, such as the Linux Screen Reader for GNOME and NonVisual Desktop Access
for Windows.
The most widely used screen readers are separate commercial products: JAWS from Freedom Scientific
, Window-Eyes
from GW Micro, Dolphin Supernova by Dolphin, System Access from Serotek, and ZoomText Magnifier/Reader from Ai Squared are prominent examples in the English-speaking market.
, which employed command line interfaces (CLIs), the screen display consisted of characters mapping directly to a screen buffer
in memory and a cursor position. Input was by keyboard. All this information could therefore be obtained from the system either by hooking
the flow of information around the system and reading the screen buffer or by using a standard hardware output socket and communicating the results to the user. This was relatively easy to engineer.
In the 1980s, the Research Centre for the Education of the Visually Handicapped (RCEVH) at the University of Birmingham developed Screen Reader for the BBC Micro and NEC Portable.
s (GUIs), the situation became more complicated. A GUI has characters and graphics drawn on the screen at particular positions, and therefore there is no purely textual representation of the graphical contents of the display. Screen readers were therefore forced to employ new low-level techniques, gathering messages from the operating system
and using these to build up an "off-screen model", a representation of the display in which the required text content is stored.
For example, the operating system might send messages to draw a command button and its caption. These messages are intercepted and used to construct the off-screen model. The user can switch between controls (such as buttons) available on the screen and the captions and control contents will be read aloud and/or shown on refreshable Braille display.
Screen readers can also communicate information on menus, controls, and other visual constructs to permit blind users to interact with these constructs. However, maintaining an off-screen model is a significant technical challenge: hooking the low-level messages and maintaining an accurate model are both difficult tasks.
. Existing APIs include:
Screen readers can query the operating system or application for what is currently being displayed and receive updates when the display changes. For example, a screen reader can be told that the current focus is on a button and the button caption to be communicated to the user. This approach is considerably easier for screen readers, but fails when applications do not comply with the accessibility API: for example, Microsoft Word
does not comply with the MSAA API, so screen readers must still maintain an off-screen model for Word or find another way to access its contents. One approach is to use available operating system messages and application object models to supplement accessibility APIs: the Thunder screenreader operates without an off-screen model in this way. (Note: the latest version of Thunder also includes an off-screen model but has one that does not involve installing a device driver. Consequently it can be used on a memory stick without any files needing to be installed.)
Screen readers can be assumed to be able to access all display content that is not intrinsically inaccessible. Web browsers, word processors, icons and windows and email programs are just some of the applications used successfully by screen reader users. However, using a screen reader is, according to some users, considerably more difficult than using a GUI and many applications have specific problems resulting from the nature of the application (e.g. animations in Macromedia Flash) or failure to comply with accessibility standards for the platform (e.g. Microsoft Word and Active Accessibility).
and can be a form of assistive technology
if they are designed to remove the need to use a screen reader.
is announced or silently ignored. Some screen readers can be tailored to a particular application through scripting. One advantage of scripting is that it allows customizations to be shared among users, increasing accessibility for all. JAWS enjoys an active script-sharing community, for example.
, providing that the language of the material is encoded in its metadata
.
Some screen reading programs also include language verbosity, which automatically detects verbosity settings related to speech output language. For example, if a user navigated to a website based in the United Kingdom, the text would be read with an English accent.
Application software
Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...
that attempts to identify and interpret what is being displayed on the screen (or, more accurately, sent to standard output
Standard streams
In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...
, whether a video monitor is present or not). This interpretation is then re-presented to the user with text-to-speech, sound icons, or a Braille output device
Refreshable Braille display
A refreshable Braille display or Braille terminal is an electro-mechanical device for displaying Braille characters, usually by means of raising dots through holes in a flat surface. Blind computer users, who cannot use a normal computer monitor, use it to read text output...
. Screen readers are a form of assistive technology
Assistive technology
Assistive technology or adaptive technology is an umbrella term that includes assistive, adaptive, and rehabilitative devices for people with disabilities and also includes the process used in selecting, locating, and using them...
(AT) potentially useful to people who are blind
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
, visually impaired
Visual impairment
Visual impairment is vision loss to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive...
, illiterate or learning disabled
Learning disability
Learning disability is a classification including several disorders in which a person has difficulty learning in a typical manner, usually caused by an unknown factor or factors...
, often in combination with other AT, such as screen magnifier
Screen magnifier
A screen magnifier is software that interfaces with a computer's graphical output to present enlarged screen content. It is a type of assistive technology suitable for visually impaired people with some functional vision; visually impaired people with little or no functional vision usually use a...
s.
A person's choice of screen reader is dictated by many factors, including platform, cost (even to upgrade a screen reader can cost hundreds of U.S. dollars), and the role of organizations like charities, schools, and employers. Screen reader choice is contentious: differing priorities and strong preferences are common.
Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
operating systems have included the Microsoft Narrator
Microsoft Narrator
Narrator is a light-duty screen reader utility included in Microsoft Windows. Narrator reads dialog boxes and window controls in a number of the more basic applications for Windows....
light-duty screen reader since Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
. Apple Inc. Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
includes VoiceOver
VoiceOver
VoiceOver is a screen reader built into Apple Inc.'s Mac OS X, iOS and iPod operating systems. By using VoiceOver, the user can access their Macintosh or iOS device based on spoken descriptions and, in the case of the Mac, the keyboard. The feature is designed to increase accessibility for blind...
, a feature-rich screen reader. The console-based Oralux
Oralux
Oralux is an association whose objective is to foster digital accessibility using solutions based upon Free Software and open standards. The association proposes Voxin, an easily installable add-on which provides yet another text-to-speech to blind users of Linux....
Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
distribution ships with three screen-reading environments: Emacspeak
Emacspeak
Emacspeak is a free computer application, a speech interface and an audio desktop employing Emacs, which is written in C, Emacs Lisp and Tcl and developed principally by T. V. Raman and first released May 1995; it is portable to all POSIX-compatible OSs...
, Yasr and Speakup. The open source GNOME
GNOME
GNOME is a desktop environment and graphical user interface that runs on top of a computer operating system. It is composed entirely of free and open source software...
desktop environment long included Gnopernicus
Gnopernicus
Gnopernicus is a free GNOME desktop application that provides Assistive Technologies for blind and visually impaired users.SRCore is the component of Gnopernicus screen reader, that gathers information from all input sources, organize it and then presents it to the three outputs: Braille, Speech,...
and now includes Orca
Orca (assistive technology)
Orca is a free and open source, flexible, extensible assistive technology for people with visual impairments. Using various combinations of speech synthesis, braille, and magnification, Orca helps provide access to applications and toolkits that support the AT-SPI .The development of Orca has been...
.
There are also open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
screen readers, such as the Linux Screen Reader for GNOME and NonVisual Desktop Access
NonVisual Desktop Access
NonVisual Desktop Access is a free, open source, portable screen reader for Microsoft Windows. The project was started by Michael Curran in 2006. The latest stable version is 2011.3NVDA is programmed in Python...
for Windows.
The most widely used screen readers are separate commercial products: JAWS from Freedom Scientific
Freedom Scientific
Freedom Scientific is a corporation which researches, creates, and sells technology intended for people who are blind or have low vision and those with learning disabilities. The company's Blind and Low Vision Group's products include software and hardware to help people with low vision work with...
, Window-Eyes
Window-eyes
Window-Eyes is a screen reader for Microsoft Windows, developed by GW Micro. The first version was released in 1995. The latest version of Window-Eyes is 7.2, released in 2010. and version 7.5.1 was realsed on march 14 2011-Features:...
from GW Micro, Dolphin Supernova by Dolphin, System Access from Serotek, and ZoomText Magnifier/Reader from Ai Squared are prominent examples in the English-speaking market.
CLI (text) screen readers
In early operating systems, such as MS-DOSMS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
, which employed command line interfaces (CLIs), the screen display consisted of characters mapping directly to a screen buffer
Screen buffer
In computing, screen buffer is a part of computer memory used by a computer application for the representation of the content to be shown on the computer display....
in memory and a cursor position. Input was by keyboard. All this information could therefore be obtained from the system either by hooking
Hooking
In computer programming, the term hooking covers a range of techniques used to alter or augment the behavior of an operating system, of applications, or of other software components by intercepting function calls or messages or events passed between software components...
the flow of information around the system and reading the screen buffer or by using a standard hardware output socket and communicating the results to the user. This was relatively easy to engineer.
In the 1980s, the Research Centre for the Education of the Visually Handicapped (RCEVH) at the University of Birmingham developed Screen Reader for the BBC Micro and NEC Portable.
Off-screen models
With the arrival of graphical user interfaceGraphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
s (GUIs), the situation became more complicated. A GUI has characters and graphics drawn on the screen at particular positions, and therefore there is no purely textual representation of the graphical contents of the display. Screen readers were therefore forced to employ new low-level techniques, gathering messages from the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
and using these to build up an "off-screen model", a representation of the display in which the required text content is stored.
For example, the operating system might send messages to draw a command button and its caption. These messages are intercepted and used to construct the off-screen model. The user can switch between controls (such as buttons) available on the screen and the captions and control contents will be read aloud and/or shown on refreshable Braille display.
Screen readers can also communicate information on menus, controls, and other visual constructs to permit blind users to interact with these constructs. However, maintaining an off-screen model is a significant technical challenge: hooking the low-level messages and maintaining an accurate model are both difficult tasks.
Accessibility APIs
Operating system and application designers have attempted to address these problems by providing ways for screen readers to access the display contents without having to maintain an off-screen model. These involve the provision of alternative and accessible representations of what is being displayed on the screen accessed through an APIApplication programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
. Existing APIs include:
- Apple Accessibility API
- AT-SPI
- IAccessible2IAccessible2IAccessible2 is a new accessibility API for Microsoft Windows applications. Initially developed by IBM under the codename Project Missouri, IAccessible2 has been placed under the aegis of the Free Standards Group, now part of the Linux Foundation...
, - Microsoft Active AccessibilityMicrosoft Active AccessibilityMicrosoft Active Accessibility is an Application Programming Interface for user interface accessibility. MSAA was introduced as a platform add-on to Microsoft Windows 95 in 1997...
(MSAA) - Microsoft UI AutomationMicrosoft UI AutomationMicrosoft UI Automation is an Application Programming Interface for User Interface accessibility that is designed to help Assistive Technology products interact with standard and custom UI elements of an application as well as to access, identify, and manipulate an application's UI elements...
- Java Access Bridge
Screen readers can query the operating system or application for what is currently being displayed and receive updates when the display changes. For example, a screen reader can be told that the current focus is on a button and the button caption to be communicated to the user. This approach is considerably easier for screen readers, but fails when applications do not comply with the accessibility API: for example, Microsoft Word
Microsoft Word
Microsoft Word is a word processor designed by Microsoft. It was first released in 1983 under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platforms including IBM PCs running DOS , the Apple Macintosh , the AT&T Unix PC , Atari ST , SCO UNIX,...
does not comply with the MSAA API, so screen readers must still maintain an off-screen model for Word or find another way to access its contents. One approach is to use available operating system messages and application object models to supplement accessibility APIs: the Thunder screenreader operates without an off-screen model in this way. (Note: the latest version of Thunder also includes an off-screen model but has one that does not involve installing a device driver. Consequently it can be used on a memory stick without any files needing to be installed.)
Screen readers can be assumed to be able to access all display content that is not intrinsically inaccessible. Web browsers, word processors, icons and windows and email programs are just some of the applications used successfully by screen reader users. However, using a screen reader is, according to some users, considerably more difficult than using a GUI and many applications have specific problems resulting from the nature of the application (e.g. animations in Macromedia Flash) or failure to comply with accessibility standards for the platform (e.g. Microsoft Word and Active Accessibility).
Self-voicing applications
Some programs speak or make other sounds so that they can be used by blind people or people who cannot see the screen. These programs are termed self-voicingSelf-voicing
A self-voicing application is an application that provides an aural interface without requiring a separate screen reader. Self-voicing applications can be an important form of assistive technology, useful to those who have difficulty reading or seeing....
and can be a form of assistive technology
Assistive technology
Assistive technology or adaptive technology is an umbrella term that includes assistive, adaptive, and rehabilitative devices for people with disabilities and also includes the process used in selecting, locating, and using them...
if they are designed to remove the need to use a screen reader.
Web-based screen readers
A relatively new development in the field is web-based applications like Spoken-Web that is web portal, managing content like news updates, weather, science and business articles for visually impaired or blind computer users. Other examples are ReadSpeaker or BrowseAloud that add text-to-speech functionality to web content. The primary audience for such applications is those who have difficulty reading because of learning disabilities or language barriers. Although functionality remains limited compared to equivalent desktop applications, the major benefit is to increase the accessibility of said websites when viewed on public machines where users do not have permission to install custom software, giving people greater 'freedom to roam'.Screen reader customization
Not only do screen readers differ widely from each other, but most are highly configurable. For example, most screen readers allow the user to select whether most punctuationPunctuation
Punctuation marks are symbols that indicate the structure and organization of written language, as well as intonation and pauses to be observed when reading aloud.In written English, punctuation is vital to disambiguate the meaning of sentences...
is announced or silently ignored. Some screen readers can be tailored to a particular application through scripting. One advantage of scripting is that it allows customizations to be shared among users, increasing accessibility for all. JAWS enjoys an active script-sharing community, for example.
Emulators
- Fangs screen reader emulator - An open source Mozilla Firefox extension that simulates how a web page would look in JAWS.
Verbosity
Verbosity is a term used to describe a feature of screen reading software that support vision-impaired computer users. Speech verbosity controls enable users to choose how much speech feedback they wish to hear. Specifically, verbosity settings allow users to construct a mental model of web pages displayed on their computer screen. Based on verbosity settings, a screen-reading program informs users of certain formatting changes, such as when a frame or table begins and ends, where graphics have been inserted into the text, or when a list appears in the document.Language
Some screen readers can read text in more than one languageLanguage
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...
, providing that the language of the material is encoded in its metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
.
Some screen reading programs also include language verbosity, which automatically detects verbosity settings related to speech output language. For example, if a user navigated to a website based in the United Kingdom, the text would be read with an English accent.
See also
- List of screen readers
- Screen magnifierScreen magnifierA screen magnifier is software that interfaces with a computer's graphical output to present enlarged screen content. It is a type of assistive technology suitable for visually impaired people with some functional vision; visually impaired people with little or no functional vision usually use a...
- Self-voicingSelf-voicingA self-voicing application is an application that provides an aural interface without requiring a separate screen reader. Self-voicing applications can be an important form of assistive technology, useful to those who have difficulty reading or seeing....
- Speech processingSpeech processingSpeech processing is the study of speech signals and the processing methods of these signals.The signals are usually processed in a digital representation, so speech processing can be regarded as a special case of digital signal processing, applied to speech signal.It is also closely tied to...
- Speech recognitionSpeech recognitionSpeech recognition converts spoken words to text. The term "voice recognition" is sometimes used to refer to recognition systems that must be trained to a particular speaker—as is the case for most desktop recognition software...
- Text to speech