An incoherent optical data-processing method is described, which has the potential for performing discrete Fourier transforms of short length at rates far exceeding those afforded by both special-purpose digital hardware and representative coherent optical processors.

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A key source of digital images is the electro-optical imaging sensor. The basic characteristic that identifies a digital electro-optical sensor is conversion of reflected or emitted light from a scene or object into a digital image signal. Examples include television cameras with digital output, and scanning or staring cameras with digital output. We describe general system design techniques to derive optimum imaging sensor specifications, and we offer examples for two applications. One example application is for terrestrial thermal imaging of nearby objects, such as vehicles. The other example is a sensor to create a color image of small targets in low-light, such as an automobile license plate from a distance of several meters. 0 1993 John Wiley & Sons, Inc. TYPES OF IMAGING SENSORSWe arbitrarily distinguish two categories of imaging sensors of common interest: motion-video systems and still camera systems. There is no fundamental difference in the basic design principles associated with the two, but the applications are markedly different. Motion video places extra demands on the signal transmission systems used to read the system image output from the imaging sensor. Therefore, a motion-video system often is used to provide visible television images for human viewing. It seldom provides the accurate radiometric measurements of the reflected or emitted light from an object often required of still picture sensors.Therefore, it is often (perhaps surprisingly) easier and cheaper to design and build a motion-video system than it is to build a carefully calibrated still camera system with digital imaging capability. In fact, solid-state video cameras and video cassette recorders (VCRs) with digital image processing features have been on the consumer market for several years, but still-picture solid-state cameras with digital output were introduced more recently. Table I lists several general examples of digital imaging systems in both categories.A. Motion-Video Digital Imaging Systems. Standard television vidicon cameras can be used as components of digital imaging systems by attaching sampling analog-to-digital image data converters to the vidicon video signal output. In fact, the National Television Standards Committee (NTSC) specifies a very simple %bit format that allows one to purchase off-theshelf conversion units just for the purpose of interfacing standard vidicon TV cameras to computers [l]. Now even low-cost personal computers can be interfaced to TV cameras Received IS March 1989; revised manuscript received 21 September 1Y92 to produce digitized images of acceptable quality for many applications.Solid-state video cameras are also becoming more prevalent, and these systems offer the convenience of smaller size, weight, and power consumption than conventional vidicon cameras [2-41. A t the same time these systems generally d o not saturate in response to very bright objects in a scene, such as birthday candle flames, which create undesirable flare in vidicon images. Solid-state cameras also offer ...