A 256 × 256-pixel smart CMOS image sensor for line based stereo vision applications

This paper presents a 256×256-pixel smart CMOS image sensor destined to line based vision applications. By combining the edge based analog processing technique with active pixel CMOS image sensor matrix, a dense and fast image processing has been achieved. The on-chip processing includes: 1° analog histogram equlizer; 2° programmable recursive Gaussian filter; 3° a spatio-temporal differentiator; and 4° a local extrema extractor. A moving blade shutter is applied to the APS matrix in order to adapt the exposure time according to global illumination level. The on-chip, histogram equlizer can extend the image contrast to a constant and optimal range for all the following processing operators. This local image signal regularization gives a constant signal amplitude and permits a stable and predictable precision of other analog signal processing. A prototype chip has been designed and fabricated in a standard 0.8µ CMOS process with double poly and double metal. The pixel pitch is fixed at 20µm and gives a total chip area of about 7×7mm2. A line processing time is measured at 50µS and a frame rate of 50 can be easily obtained. The worst case power consumption is measured at 40mA @ 5V.