An optical correlation device (10) for correlating an image of an object to be inspected with an image of a reference object, the device uses a reflective spatial light modulator (12a, 12b) for modulating the two phases. The first spatial light modulator 12a receives the electronic input in the form of image data representing the inspected object. This modulator modulates the incoming light 15 with this input and reflects the output modulated by the first Fourier lens 13. This lens provides an optical input to a second spatial light modulator 12b, whose electronic input is transformation data representing the complex conjugate of the Fourier transform of the reference image. The electronic input modulates the optical input, resulting in a Fourier product of the two images and is transformed to provide correlation data.
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