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Parallel implementation of the Karhunen-Loeve procedure for image recognition

The Karhunen-Loeve (K-L) transform is very useful in image representation and classification. However, the parallel implementation of it through some optical methods have rarely been investigated. In this paper, we constructed a photorefractive crystal based optical processor and implemented the time-consuming projection operations of the K-L transform in parallel so that the speed of the image processing can be greatly improved. In our approach, a set of eigenimages extracted from a large number of training images by K-L transform are stored in the crystal by using the two-wave mixing technique. When any new image inputs the processor, spatially separated beams with different light intensities are obtained in parallel. The intensity of each beam just represents the projection result between the input image and each eigenimage. The high speed can sufficiently demonstrate the advantage of the optical computing based parallel architecture for image processing.