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We present a new slot-in type of optical correlator that is more compact than the previous types. The correlator can fit inside the cabinet of commercial personal computers and is fully controllable with windows-based software. The correlator is a Joint Transform type (JTC) and its optical system fits inside a metal box measuring 140 mm (W) x 220 mm (L) x 40 mm (H). The optical source is a 650-nm-band laser diode of the kind used in DVD systems. A spatial light modulator and a CMOS camera are installed in the metal box with the passive optical components required for the JTC. The collimated light from the laser diode is illuminated on the spatial light modulator displaying reference and data to be examined. The light reflected from the modulator is Fourier-transformed by a lens on the plane of the CMOS camera. The computer reads the power spectrum recorded by the camera and modulates the spatial light modulator. This process is repeated. We found that these JTC processes could be performed with the prototype developed in this study.

We propose a new technique for retrieving color information. The color data taken by a digital camera is transferred to two-dimensional data on the color chart and displayed on a spatial light modulator. This modulation technique is combined with a retrieval technique using a joint transform correlator. The color data, e.g., photograph of a flower, are retrieved by this system, and the same color data (photograph) can be perfectly selected from the many reference data. This technique will open a new area of retrieval techniques for ambiguous images based on shape and color information.