Making graphics accessible to the visually impaired
A number of technical aids are already available for access to textual information in electronic representation for blind users, such as optical character recognition, screen readers or braille devices. The TeDUB project focused on the content of informational graphics like technical diagrams, aiming to grant blind users access to graphically represented information. Information contained in graphics like technical diagrams, are inherently hard to grasp for people who cannot see. However, the studies performed within the TeDUB project gave important insight into the way blind people build up mental representations of verbally described diagrams. More specifically, a strong tendency towards hierarchical structures having a semantically defined entry point and a recognizable order of items was unveiled. Based on these findings in the TeDUB system, a diagram is represented by a layered partonomic composition of different abstraction levels. In a partonomic hierarchy, two elements are related if one is a part of the other. The basic information contained in the technical drawings is extracted using image-processing methods. In the TeDUB system, technical diagrams are converted into a connected graph of diagram components, starting from the lowest up to the highest. Each part is defined in terms of its parts and the relations between them. In addition a network of hypotheses and processes are incrementally used until a semantic description of the whole diagram is found. An assumed part is a hypothesis that is assigned a certain degree of confidence. Starting from the lowest level, a logical inference mechanism is used to stepwise infer new parts from existing ones and finally aggregate lower level syntactic constructs to increasingly domain dependent semantic units. The partonomic hierarchy can encompass an arbitrary number of semantic as well as geometric levels. The information of the diagram is presented by TeDUB as a network of connected nodes, which can be navigated with the keyboard and a joystick. The TeDUB system aims at being domain independent. That makes the presentation by a partonomic hierarchy of great value since it enables semantic-based retrieval of technical drawings by blind domain experts.