Multiframe averaging and homomorphic filtering for clarification of dark and shadowed video scenes
S. G. Burgiss, S.G. Goodridge · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2001
In order to clarify detail of objects in shadows, we present a combination of frame averaging and homomorphic filtering. Multi-frame averaging allows exploitation of temporal redundancy in video to reduce noise present in dark scenes. One common method to enhance images suffering from low contrast is gain. Gain has the side effect of saturating brighter areas of the scene. Homomorphic filtering allows the effects of differing illumination conditions to be equalized across a scene. This is accomplished by applying a spatial high-pass filter to the natural log of pixel values. By following frame averaging with homomorphic filtering, details obscured by shadows may be clarified without losing important foreground information. Noise reduction through frame averaging greatly improves the results of homomorphic filtering, which usually amplifies Gaussian white noise.