The telesign project

Telesign is designed to offer a means of visual communication over a 56- or 64-kbit/s data network. The purpose is to supply a means of visual telecommunication among the members of the deaf community using sign language or lip reading. The system consists of an edge detector followed by digital compression coding to meet channel requirements. Psychometric experiments have shown the need for 25 frames/s with a minimum definition of 128 × 128 points. Edge-detection techniques are discussed from the viewpoint of an unusual quality criterion: the subjective resemblance of the contoured image to the original and, closely related to this, the intelligibility of the image sequence. A classification of edge detectors is given, based upon the position of the contour with respect to the dark/light contrast boundaries in the picture. The relationship of this classification to the quality criterion yields the definition of a new gradient display, called the "shifted gradient," with improved visual quality. The pseudo-Laplacian, well-suited to the problem, is analyzed. Various binary coding techniques are reviewed, and the results of compression given. A psychovisual experiment, performed in conjunction with the INJS (National Institute for the Education of Young Deaf), Paris, France, is described; the results validate the proposed approach. Guidelines are proposed for the design of a real-time device. The application of Telesign to closed-caption TV programs for the deaf viewer is also suggested.