This research project on making accessible bit map graphics accessible was started in 1997 and has now ended because of the emergence of the far superior accessibility of Scalable Vector Graphics (SVG). Our work on SVG is described elsewhere in this graphics access section. However we learned a great deal from this bit map graphics work and retain this description as an archive of a successful research enroute to a more successful product based on something better than bit mapped graphics.
A bit map image is essentially inaccessible, because the visual appearance can seldom be translated into an audio or a tactile image that is easily recognized by a person with a severe print disability.
We have developed a relatively simple method that permits authors or editors to "make bit maps accessible" by adding identifying information related to objects in the figure. Accessing this information requires a Netscape or Internet Explorer browser version 4.72 or later and, for blind users, a screen reader that works with those browsers.
The most recent screen readers have begun using the document object model for access and do not respond in the way that the particular examples were designed for. This is an interesting lesson for developers not to depend on screen reader characteristics in making accessibility work-arounds. Our current SVG browser is self-voicing and screen readers need to be put to sleep in this and other self-voicing applications.Several examples are available by following the annotated examples link below. If a user clicks on the "annotated image link" adjacent to any of the bit map picture examples, the image is moved to the top frame of a new double frame window. As the mouse pointer is moved from object to object in the top frame, the label for each object is displayed in the bottom frame.
Before trying this there are two very important things to know. In order to overcome limitations of Internet Explorer it is usually necessary to maximize the screen once this annotated image window is displayed. Maximize by pressing ALT, then down arrow, then x. The second caveat is that users with any browser should return by closing the window, not by going back. Going back will usually take you through a long succession of ghosts created while you explored various image labels.
Older generation screen readers normally triggered on any change and read the labels as they appeared. Current screen readers can still give access, but it is more cumbersome. Long or confusing labels may be browsed by the screen reader in review mode.
A blind user will find it most convenient to explore the image with a digitizing pad instead of a mouse. Ideally she/he will have a tactile image on the digitizing pad.
Several examples of annotated bitmaps.
We have also developed methods that permit users to select an object from the object list and locate it on the image map. The first generation research "audio locator" is illustrated in the example US map image whose accessibility link includes the audio locator. This example works properly only with Netscape 4 browsers at this time.
A sighted user can click on the object list in the bottom frame, then click the find-it button. We recommend that anyone who wants or needs to use keyboard navigation move through links backward by using SHIFT TAB to the Find-it button, then once more to the object list. It is possible to TAB forward, but one must tab through each object in the image first, and this can be quite tedious.
Choose an object in the object list by using the up/down arrows to move through the list. Then TAB to the Find-it button and press ENTER.
When the mouse pointer is now moved to an object within the image, its name will appear as usual, and, unless this is the object being searched, a series of bell sounds will begin. If the bell is heard from the right speaker, it means that the center point of the search object is located to the right of the current mouse pointer. If from the left speaker the search object is to the left. If the bell tone is high, it means that the center of the search object is located above the current mouse pointer position. If the tone is low, the object is below the mouse pointer.
The mouse pointer can now be moved left/right and up/down until the search object is located. If the sound changes from the right to the left speaker, it means that the pointer has moved above or below the search object so that its center point is now left of the mouse pointer. If the bell changes from a high to low tone, it means that the mouse pointer has moved past the object from a place below the center of the object to a place above the center of the object. When the pointer moves into the object itself, a short musical sound indicates that it has been found. With a little practice, a user can locate objects very quickly.
Link to US map accessible image with audio locator
Last update March 6, 2001