Abstract
This paper reviews the state of the art in the field of assistive devices for sight-handicapped people. It concentrates in particular on systems that use image and video processing for converting visual data into an alternate rendering modality that will be appropriate for a blind user. Such alternate modalities can be auditory, haptic, or a combination of both. There is thus the need for modality conversion, from the visual modality to another one; this is where image and video processing plays a crucial role. The possible alternate sensory channels are examined with the purpose of using them to present visual information to totally blind persons. Aids that are either already existing or still under development are then presented, where a distinction is made according to the final output channel. Haptic encoding is the most often used by means of either tactile or combined tactile/kinesthetic encoding of the visual data. Auditory encoding may lead to low-cost devices, but there is need to handle high information loss incurred when transforming visual data to auditory one. Despite a higher technical complexity, audio/haptic encoding has the advantage of making use of all available user's sensory channels.
Highlights
VISUAL HANDICAP AND ASSISTIVE DEVICESVisual impairment can be quantified in terms of the remaining visual acuity and visual field
The possible alternate sensory channels are examined with the purpose of using them to present visual information to totally blind persons
According to the 10th Revision of the World Health Organization (WHO) International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 6/18, but equal to or better than 3/60, or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction
Summary
Visual impairment can be quantified in terms of the remaining visual acuity and visual field. Hatwell assumed that haptic spatial perceptions from congenitally blind people are systematically less efficient than for the late blind persons This comes from the visual-haptic cross-modal transfer that took place during the infancy of the late blind and which increased the spatial perceptual quality of such sensory system. This set of observations showed that early and late blind people are able to generate mental images, the process is harder for early blind persons. The following sections review various assistive devices for totally blind users, classified according to the alternate modality used This classification was preferred over one based on which image/video processing techniques are employed, as many systems use a variety of techniques.
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