Differentiation and subtraction of amplitude and phase images using a photorefractive novelty filter

In this article, we demonstrate the capability of a two-beam coupling photo refractive optical novelty filter of detecting changes in the amplitude or phase of optical images. These changes may either be continuous or discrete in time. The performance of the two-beam coupling novelty filter is invest igated and expressions for the output contrast corresponding to phase and a mplitude changes based on a novel, simple interference model of two-beam co upling are derived. These expressions are verified by experimental results on the novelty contrast, revealing that the amplitude contrast is not descr ibed correctly by the commonly accepted coupled-wave theory. The novelty fi lter was applied to the detection of temporally continuous phase changes pr ovided by a gas flow and moving microscopic objects. A novel scheme for ima ge subtraction is also demonstrated, showing the novelty filter's ability t o detect temporally discrete changes.