Providing Alternatives for Images
One important WAI requirement is to ensure that every image used on a Web page is ac-companied by a textual description that clearly defines the purpose of the image. To accomplish this task, include a text equivalent of each item by using the alt attribute of the img and input tags. A text equivalent for images defined using the object element is the text between the start and end <object> tag.
Web developers who do not use the alt attribute to provide text equivalents increase the difficulty people with visual impairments experience in navigating the Web. Special-ized user agents, such as screen readers (programs that allow users to hear all text and text descriptions displayed on their screen) and braille displays (devices that receive data from screen-reading software and output the data as braille), allow people with visual impair-ments to access text-based information that is normally displayed on the screen. A user agent visually interprets Web-page source code and translates it into formatted text and images. Web browsers, such as Microsoft Internet Explorer and Netscape Communicator, and the screen readers mentioned throughout this chapter are examples of user agents.
Web pages that do not provide text equivalents for video and audio clips are difficult for people with visual and hearing impairments to access. Screen readers cannot read images, movies and most other non-XHTML objects from these Web pages. Providing multimedia-based information in a variety of ways (i.e., using the alt attribute or pro-viding in-line descriptions of images) helps maximize the content’s accessibility.
Web designers should provide useful text equivalents in the alt attribute for use in nonvisual user agents. For example, if the alt attribute describes a sales growth chart, it should provide a brief summary of the data; it should not describe the data in the chart. Instead, a complete description of the chart’s data should be included in the longdesc attribute, which is intended to augment the alt attribute’s description. The longdesc attribute contains the URL that links to a Web page describing the image or multimedia content. Currently, most Web browsers do not support the longdesc attribute. An alter-native for the longdesc attribute is D-link, which provides descriptive text about graphs and charts. More information on D-links can be obtained at the CORDA Technologies Web site (www.corda.com).
Using a screen reader for Web-site navigation can be time consuming and frustrating, as screen readers cannot interpret pictures and other graphical content. A link at the top of each Web page that provides direct access to the page’s content could allow users to bypass a long list of navigation links or other inaccessible elements. This jump can save time and eliminate frustration for individuals with visual impairments.
Emacspeak is a screen interface that allows greater Internet access to individuals with visual disabilities by translating text to voice data. The open source product also imple-ments auditory icons that play various sounds. Emacspeak can be customized with Linux operating systems and provides support for the IBM ViaVoice speech engine. The Emacs-peak Web site is located at www.cs.cornell.edu/home/raman/emacspeak/ emacspeak.html.
In March 2001, We Media introduced the “WeMedia Browser,” which allows people with poor vision and cognitive disabilities (e.g., dyslexia) to use the Internet more conve-niently. The WeMedia Browser improves upon the traditional browser by providing over-sized buttons and keystroke commands for navigation. The user can control the speed and volume at which the browser “reads” Web page text. The WeMedia Browser free download is available at www.wemedia.com.
IBM Home Page Reader (HPR) is another browser that “reads” text selected by the user. The HPR uses the IBM ViaVoice technology to synthesize a voice. A trial version of HPR is available at www-3.ibm.com/able/hpr.html.
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