Simple 1-D image enhancement for head-mounted low vision aid

High-contrast binary images (black and white without shades of gray) were demonstrated to improve face recognition performance by the visually impaired using static images (Peli et al., Invest Ophthalmol Vis Sci 1991;32:2337-2350). A binary head-mounted display device has now been adapted to present video in real time for testing as a low vision mobility aid (an electronic telescope). When used for text presentation (as a head-mounted CCTV), a single threshold produces satisfactory performance. However, binarization of a video signal through a single threshold results in high-contrast but extremely poor image detail. A more detailed binary image can be obtained by applying bandpass filtering prior to thresholding. The application of the adaptive 2-D enhancement technique used by the DigiVision device enables such live bandpass processing and provides substantial improvement. To reduce the cost, weight, and power consumption of a portable low vision aid, a one dimensional (1-D) analog video processing alternative has been designed and implemented. Since the processing is applied only across the horizontal dimension, it provides no enhancement of horizontal features in the image. However, in this head-mounted camera application the user can easily resolve such details by a slight tilt of the head. The 1-D enhancement alternative provides satisfactory quality, high-contrast binary imaging at substantial savings.