21 cm X 31 cm optical correlator. This function mostly carries information about the object to be detected, and possibly about other objects, noise and clutter to be rejected. After a second optical Fourier transform, correlation peaks of high intensities are detected by a CCD camera where the objects would otherwise be reconstructed if no spectral filtering were applied. Our correlator employs two FLC SLMs that can display 256 X 256 pixel images at frame rates in excess of 1kHz. Figure 2 shows how information is processed in the system, from image acquisition to object recognition.
Information flow through the opto-electronic pattern recognition system.
PC Windows software controls the different steps. Furthermore, the use of binary edge-enhanced images has led to classification results comparable or better than those obtained with gray level images when the illumination conditions vary. Indeed, different illumination conditions of input scenes cause large fluctuations of the target and background gray levels, but very few perturbations on binary edge-enhanced images, which are mainly contour images and therefore less sensitive to illumination changes. A set of distorted input images are thus generated to train the filter to correctly classify images with similar distortions. The implementation of correlation filters usually requires SLMs that display complex-valued functions.