A Foveated Image Sensor in Standard CMOS Technology

Robert Wodnicki, Gordon W. Roberts, Martin D. Levine Department of Electrical Engineering, McGill University, Montr eal, Qu ebec, CANADA, H3A 2A7 Abstract We describe the design and implementation of a CMOS foveated image sensor for use in mobile robotic and machine vision applications. The sensor is biologically motivated and performs a spatial image transformation from Cartesian to log-polar coordinates. As opposed to traditional approaches, the sensor bene ts from a high degree of integration, minimal power consumption and ease of manufacture due to the use of a standard 1.2 m ASIC CMOS process. The prototype imager operates at 28 frames/sec when interfaced to a PC. Introduction Foveation is a biologically motivated image transformation which has attracted the interest of researchers in the elds of computer vision and robotics. Its principle advantages are the realization of a high degree of image compression as well as the property of scale and rotation invariance [2]. To date various computational implementations [3][6], as well as a fully custom CCD [2] image sensor have been proposed. While these approaches achieve adequate performance, they nevertheless su er from the need for considerable support resources such as networks of DSP processors and digital frame-grabbers. These resources may be readily available in a laboratory environment for use with a tethered robot, however truly autonomous mobile systems will require foveated sensors which are extremely compact and energy e cient. Recent advances in VLSI technology have made possible the implementation of image sensors using standard CMOS ASIC's [4]. Such image sensors bene t Presented at the Custom Integrated Circuits Conference, Santa Clara, May 3 1995. from the integration of image sensing and image processing functions on the same die, yielding a vast reduction in power consumption and system mass. These savings make possible the realization of a completely self-contained foveated image sensor for use on mobile robots. We have designed, fabricated and tested such a device for use in a robot eye for an autonomous robot system [3]. In the present discussion we summarize key design issues and give results of the functioning sensor.Foveation The concept of foveation in machine vision stems from a detailed examination of the human visual pathway [6]. The human retina can be roughly divided into two distinct regions. The fovea is a small area of very high, i, j RF