Abstract

A novelty filter is a image pre-processing element that is sensitive only to the new features in a scene. It is thus perfectly adapted to the detection of an objet appearing and moving in a complex scene. Different architecure where proposed to implement a novelty filter with a photorefractive crystal [1]. Among these different set-ups the simplest one is based on photorefractive two beam coupling. A signal beam carrying the image interferes with a pump beam in a high gain photorefractive crystal. An energy transfer occurs through two beam coupling that causes a strong attenuation of the stationnary signal beam. As soon as an objet appears in the image the condition for the attenuation of the beam disappears and ligth passes immediatly at the position of the object, and only there, until a new grating is written and restores attenuation. We use and characterize this device with the final goal of detecting very small moving object, with a very small contrast compared to the background.

© 1998 IEEE