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Abstract
It is possible to determine any Fourier coefficient (spatial frequency) in a real two-dimensional distribution of illumination by allowing the distribution to throw the shadow of a suitably placed grid onto an observation plane, where the contrast of the shadow measures the modulus of the Fourier coefficient and its position measures the phase of the coefficient. A pilot model of a scheme for reading the Arabic numerals 0, 1, …, 9 using only three Fourier coefficients has been set up and run successfully. The possibilities of the method are assessed.