A Hybrid Optical/Electronic Image Correlator

Abstract

The attraction of using optics to perform the cross-correlation of two images, is the ease with which a good quality lens generates a 2-D Fourier transform. This Fourier transform property of the lens is dependent on the use of coherent light to carry the image. Few objects are of sufficient optical flatness to allow the formation of a good coherent light image; therefore, an incoherent-to-coherent light converter, such as the Hughes liquid crystal light valve is used (1). However, it is not always convenient to image the object directly onto the light valve. In addition, a high light intensity is required. A camera which is interfaced to a passive 2-D display device of good optical quality, forms a practical alternative. When a frame store and microprocessor are added, then a limited set of images can be stored and recalled rapidly. This gives a programmable correlator (2). If an image processor is used, then a wide repertoire of pre-processing functions can be performed on the image. The disadvantage of this alternative is the frame speed reduction which is consequent on converting the image to a serial format for transmission between the camera and display device. However, for a number of applications the resolution and grey-scale rendering of the image can be reduced, thereby increasing the frame speed.