Visual impairment

Since computer interfaces often solicit visual input and provide visual feedback, another significant challenge in computer accessibility involves making software usable by people with visual impairment. For individuals with mild to medium vision impairment, it is helpful to use large fonts, high DPI displays, high-contrast themes and icons supplemented with auditory feedback and screen magnifying software.

In the case of severe vision impairment such as blindness, screen reader software that provides feedback via text to speech or a refreshable braille display is a necessary accommodation for interaction with a computer.

About 8% of people, mostly males, suffer from some form of colour-blindness. The main colour combinations that might be confused by people with visual deficiency include red/green and blue/green. However, in a well-designed user interface, color should not be the only way of distinguishing between different pieces of information.

Motor and dexterity impairments

Some people may not be able to use a conventional input device, such as the mouse or the keyboard. Therefore it is important for software functions to be accessible using both devices; ideally, software uses a generic input API that permits the use even of highly specialized devices unheard of at the time of software development. Keyboard shortcuts and mouse gestures are ways to achieve this. More specialized solutions like on-screen software keyboards and alternate input devices like switches, joysticks and trackballs are also available. Speech recognition technology is also a compelling and suitable alternative to conventional keyboard and mouse input as it simply requires a commonly available audio headset.

The astrophysicist Stephen Hawking is a famous example of a person suffering from motor disability. He uses a switch, combined with special software, that allows him to control his wheelchair-mounted computer using his remaining small movement ability. This performs as a normal computer, allowing him to research and produce his written work, and as an Augmentative and Alternative Communication and environmental control device.

Hearing impairment

While sound user interfaces have a secondary role in common desktop computing, usually limited to system sounds as feedback, software producers take into account people who can't hear, either for personal disability, noisy environments, silence requirements or lack of sound hardware. Such system sounds like beeps can be substituted or supplemented with visual notifications and captioned text (akin to closed captions).

Software accessibility

Accessibility APIs

Software API exist to allow assistive technology products (like screen readers, Text-to-speech, etc.) to work with software. The current or past APIs are:

• Microsoft Active Accessibility (MSAA) on Microsoft Windows

• Microsoft UI Automation on Microsoft Windows, replacing MSAA

• IAccessible2 on Microsoft Windows, a competitor of Microsoft UI Automation also replacing MSAA

• AT-SPI on UNIX and Linux

• Mac OS X Accessibility

• Java Accessibility and the Java Access Bridge for Java software.

Accessibility Features in Mainstream Software

Accessibility software can also make input devices easier to use at the user level:

• Keyboard shortcuts and MouseKeys allow the user to substitute keyboarding for mouse actions. Macro recorders can greatly extend the range and sophistication of keyboard shortcuts.

• Sticky keys allows characters or commands to be typed without having to hold down a modifier key (Shift, Ctrl, Alt) while pressing a second key. Similarly, ClickLock is a Microsoft Windows feature that remembers a mouse button is down so that items can be highlighted or dragged without holding the mouse button down throughout.

• Customization of mouse or mouse alternatives' responsiveness to movement, double-clicking, and so forth.

• ToggleKeys^[5] is a feature of Microsoft Windows 95 onwards. A high sound is heard when the CAPS LOCK, SCROLL LOCK, or NUM LOCK key is switched on and a low sound is heard when any of those keys are switched off.

• Customization of pointer appearance, such as size, color and shape.

• Predictive text

• Spell checkers and grammar checkers

Web accessibility

Enabling access to Web content for all users is the concern of the Web accessibility movement. Websites can be designed to be more accessible by their conformance to certain design principles.

Screen readers are of limited use when reading text from websites designed without consideration to accessibility; this can be due to the differences between spoken and written language and the complexity of text, but it is mainly due to poor page design practices. The tendency to indicate semantic meaning using methods that are purely presentational (e.g. larger or smaller font sizes, using different font colors, or images or multimedia to provide information) restricts meaningful access to some users. Therefore designing sites in accordance with Web accessibility principles helps enable meaningful access for all users.

For example, web designers can ensure that navigation and content is as plain and simple as appropriate and long texts should provide summaries.

Open accessibility framework

The Open Accessibility Framework (OAF) provides a high-level outline of the steps that must be in place for any computing platform to be considered accessible. These steps are analogous to those necessary to make the physical/built environment accessible. The OAF divides the required steps into two categories: creation and use.

The “creation” steps describe the necessary precursors and building blocks to enable developers to create accessible applications and products. They are:

1. Define what “accessible” means for the platform: It must be clear what is meant by “accessible” because this will differ according to the modality and capabilities of each platform. The definition may include accessibility features such as tabbing navigation,theming, and an accessibility API.

2. Provide accessible stock user interface elements: Pre-built “stock” user interface elements, used by application developers and authoring tools, must be implemented to make use of the accessibility features of the platform.

3. Provide authoring tools that support accessibility: The tools used by application developers and content authors must be implemented to encourage use of the accessibility features of the platform. This may include features such as encouraging the use of accessible stock user interface elements, prompting for information required to properly implement an accessibility API, and accessibility evaluation and repair tools.

The “use” steps describe what is necessary in the computing environment in which these accessible applications will run. They are:

1. Provide platform support: Computing platforms must properly implement the accessibility features that are specified in their accessibility definition. For example, the accessibility API definitions must, in fact, be implemented correctly in the program code.

2. Provide accessible application software: Accessible applications must actually be available for the platform. These applications must support the accessibility features of the platform. This may have been achieved using the accessible stock elements and authoring tools that support accessibility.

3. Provide assistive technologies: Assistive technologies (e.g. screen readers, screen magnifiers, voice input, adapted keyboards) must actually be available for the platform.