A screen reader is a software application that attempts to identify and interpret what is being displayed on the screen. This is then presented to a blind user as speech (by text-to-speech) or by driving a braille display. Screen readers are used by people with little or no functional vision and are a form of Assistive technology: people with some vision often use screen magnifiers. Speech synthesis is the artificial production of human speech. ... A refreshable Braille display is an electro-mechanical device for displaying Braille characters, usually by means of raising dots through holes in a flat surface. ... Assistive Technology (AT) is a generic term that includes assistive, adaptive, and rehabilitative devices and the process used in selecting, locating, and using them. ... A screen magnifier is software that interfaces with a computers graphical output to present enlarged screen content. ...

Types of screen reader

CLI (text) screen readers

In early operating systems such as MS-DOS which employed a Command Line Interface (CLI), 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 all 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 ^[1] and communicating the results to the user. This was relatively easy to engineer. Screen readers were developed for early personal computers such as the BBC Micro ^[2]. Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... It has been suggested that this article or section be merged with Command prompt. ... Hooking in programming is a technique employing so called hooks to make a chain of procedures as a handler. ... The BBC Micro, affectionately known as the Beeb, was an early home computer. ...

GUI screen readers

Off-screen models

With the arrival of graphical user interfaces (GUIs), the situation became more complicated. A GUI has characters and graphics drawn on the screen at particular positions, and as such there is no 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. This article or section needs a complete rewrite for the reasons listed on the talk page. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

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.

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 API. Examples include AT-SPI, Microsoft Active Accessibility and the 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 does not comply with the Microsoft Active Accessibility 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. An application programmatic interface (API) is the interface that a computer system, library or application provides in order to allow requests for services to be made of it by other computer programs, and/or to allow data to be exchanged between them. ... AT-SPI (Assistive Technology Service Provider Interface) is a toolkit-neutral way of providing accessibility facilities in application, developped by the gnome project. ... Microsoft Active Accessibility is a COM-based technology designed to improve the way accessibility aids work with applications running on Microsoft Windows. ... Microsoft Word, or Microsoft Office Word, is Microsofts flagship word processing software. ...

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 provide audio output (i.e. speech) so that they can be used by blind people or people who cannot see the screen. These programs are termed self-voicing and can be a form of assistive technology if they are designed to remove the need to use a screen reader. Assistive Technology (AT) is a generic term that includes assistive, adaptive, and rehabilitative devices and the process used in selecting, locating, and using them. ...

Some web browsers illustrate this type of program. Opera offers built in text-to-speech support but is not specifically designed for use by a blind person: the speech is supplementary to the sighted user interface. IBM's Home Page Reader, on the other hand, is designed to be wholly usable by a blind person with a keyboard or Braille display and no screen reader running. An example of a web browser (Mozilla Firefox running under Microsoft Windows). ... Opera is an Internet suite which handles common internet-related tasks, including visiting web sites, sending and receiving e-mail messages, managing contacts, and online chat. ... now. ... Home Page Reader is a computer program, a self-voicing web browser designed for people who are blind. ...

Screen reader products

Main article: List of screen readers

Many different commercial screen readers are available, with different approaches and features. For example, some screen readers can be scripted. Scripts are written for individual applications and users so the behaviour of the screen reader can be tailored to the application and user. A person's choice of screen reader is dictated by many factors, including cost — screen readers can cost many hundreds of U.S. dollars — and the role of organisations like charities and schools. Screen reader choice is contentious and strong opinions and preferences are common. Screen_reader are a form of assistive technology: programs to help people with visual impairments and blindness to use computers. ...

Most screen readers are commercial products: the market leaders in English-speaking countries are JAWS from Freedom Scientific, Window-Eyes from GW Micro and Hal from Dolphin Computer Access. Recent operating system developments have included some built-in screen readers: Microsoft Windows 2000 and XP come with a very limited built-in screen reader called Narrator which works through Active Accessibility (and so can be used for MSAA applications such as Windows Explorer and Notepad but not for Microsoft Office or Internet Explorer). Apple has built VoiceOver, a much more fully-featured screen-reader, into Mac OS X. Job Access with Speech (better known as JAWS) is a screen reader from Freedom ScientificBLV Group, LLC] for the visually impaired. ... Freedom Scientific is a corporation which researches, creates and sells technology to blind people, including software which uses voice synthesizers and the braille code. ... Window-Eyes is a screen reader that makes a computer usable by someone who is blind or is visually impaired. ... GW Micro based in Fort Wayne, Indiana is a corporation which creates technology to assist people who are blind or have low vision. ... Established in 1986, Dolphin Computer Access is a corporation who design and create software solutions for people with visual and print impairments. ... Narrator is a light-duty screen reader utility packaged with Microsoft Windows 2000 and Windows XP. Narrator reads dialog boxes and window controls. ... Microsoft Active Accessibility is a COM-based technology designed to improve the way accessibility aids work with applications running on Microsoft Windows. ... Apple Computer, Inc. ... A voice-over is a narration that is played on top of a video segment, usually with the audio for that segment muted or lowered. ... Mac OS X (officially pronounced Mac Oh-Ess Ten) is a line of open source graphical operating systems, with proprietary higher level API layers, developed, marketed, and sold by Apple Computer, the latest of which is pre-loaded on all currently shipping Macintosh computers. ...

Other screen readers, such as Virgo from Baum, are sold as part of a package with a Braille display, allowing users of the Braille display to access their computer. Screen magnifiers often come with some rudimentary speech, such as reading items under the mouse cursor. Other products such as SuperNova from Dolphin Computer Access combine full screen reading with magnification and Braille. A refreshable Braille display is an electro-mechanical device for displaying Braille characters, usually by means of raising dots through holes in a flat surface. ... A screen magnifier is software that interfaces with a computers graphical output to present enlarged screen content. ... Established in 1986, Dolphin Computer Access is a corporation who design and create software solutions for people with visual and print impairments. ...

There are also Open Source screen readers at varying levels of ability, including the Linux-based and powerful Emacspeak [3] and the less developed BRLTTY and suse-blinux, for unix text consoles and gnopernicus, Orca, and Linux Screen Reader for unix graphical applications exporting the AT-SPI interface. There is also the CLC-4-TTS Suite which works on multiple operating systems (Windows, Mac, and Linux), although it is currently limited to just reading for the Firefox web browser. Open source refers to projects that are open to the public and which draw on other projects that are freely available to the general public. ... Emacspeak is a free screen reader for Emacs which is written in C, Emacs Lisp and Tcl and developed principally by T. V. Raman (himself blind since childhood, and who has worked on voice software with Adobe Software and later IBM) and first released May 1995; it is portable to... Gnopernicus is a free GNOME desktop application that provides Assistive Technologies (AT) for blind and visually impaired person. ... AT-SPI (Assistive Technology Service Provider Interface) is a toolkit-neutral way of providing accessibility facilities in application, developped by the gnome project. ... Firefox may refer to: Firefox (novel), written by Craig Thomas, published in 1978 Firefox (film), the 1982 movie starring Clint Eastwood, based on the novel Firefox (arcade game), the laserdisc arcade game based on the movie Mozilla Firefox, a web browser The Red Fox or the Red Panda, based on...

A relatively new development in the field is web-based applications, using Ajax methods to provide text to speech assistive functionalities to web sites and pages, such as Talklets. Although functionality is currently limited compared to some of the desktop applications available, the major benefit is the 'freedom to roam' this offers the user, as no admin rights are required on the machine being used. Ajax, shorthand for Asynchronous JavaScript and XML, is a web development technique for creating interactive web applications. ... Speech synthesis is the artificial production of human speech. ...

References

1. ↑  Talking Terminals. BYTE, September 1982. Retrieved on September 7, 2006.
2. ↑  Access to personal computers using speech synthesis. RNIB New Beacon No.76, May 1992. Retrieved on August 17, 2005.