An optical feature detection sensor based on orientation decomposition

Abstract

We have fabricated a CMOS optical sensor which detects linestops for the edges of four orientations and the corners of an input image. The sensor measures 6.8mm×6.9mm and contains an array of 11×11 pixels. Each pixel consists of phototransistors, an orientation sensor, four memory units, and a spatial filtering unit (SFU). The phototransistor is shared among four adjacent pixels. The sensor first decomposes an input image into four orientations (0deg, 45deg, 90deg, 135deg) by an array of orientation sensors. Each orientation sensor determines the local orientation according to the illumination pattern on phototransistors located at the four corners of a pixel. The SFU and the memory units perform a series of spatial filtering far each of these orientations to detect the image features. Spatial filtering is realized by convolution and threshold operations. Selection of convolution kernel and threshold determines which of the following filtering functions is performed: line completion, elimination of isolated points, line elongation, or linestop detection. Convolution is realized by a current mirror circuit, Experimental results show that the sensor is fully functional and the processing time to detect these features is about 200μsec.