Orientation-selective edge enhancement of phase objects

We present a method for the orientation-selective enhancement of the first derivatives −i.e. the edges− of a pure phase object. The proposed method is based on the transport-of-intensity equation (TIE). The TIE contains a term proportional to the scalar product of the phase gradient and an intensity gradient, which plays the role of amplifying factor of the first derivatives. We will show that if the intensity gradient is implemented in the optical setup as a moving amplitude mask with a relatively sharp border −or eventually, a digital shifting mask displayed in a liquid crystal display− it is possible to generate a synthetic image of the phase object with enhanced edges. The proposed technique is potentially useful in biological and biomedical research. Validation experiments and preliminary qualitative results illustrating the generation of synthetic images with enhanced edges are presented.