Digital zoom for low-vision enhancement systems

Zoom magnification is an essential element of video-based low vision enhancement systems. However, since optical zoom systems are bulky and power intensive, digital zoom is an attractive alternative. This paper determines the visual acuity of 15 subjects when a letter chart is viewed through a video system with various levels of digital zoom. A strategy in which the 1:1 magnified image is obtained by combining optical magnification with digital minification gives the best result, provided background scene information is know from the other cameras. A real-time FPGA based system for simultaneous zoom and smoothing is also demonstrated for text reading and enhancement.