Moiré effect as a tool for image processing

We produce the difference between two images I1(x,y) and I2(x,y) and the derivative ∂I(x, y)/∂x. We also produce pointwise nonlinearities, described by terms such as threshold, saturation, and nonmonotonic nonlinearity. Our procedure consists of three steps: encoding by spatial pulse modulation, multiplying by a spatial local oscillator, and low-pass filtering. Expressed in optical terms, we perform some moiré experiments.