Homomorphic processing system and ratio rule for color image enhancement

Homomorphic filter is an illumination-reflectance model that can be used to develop a frequency domain procedure for improving the appearance of an image by simultaneous gray-level range compression and contrast enhancement. Many previously reported methods on homomorphic filter for color images shows that the homomorphic filter consistently provides excellent dynamic range compression but is lacking final color rendition. We present a novel color image enhancement process to overcome this limitation. The color image enhancement process involved using a neural network algorithm, namely ratio rule, to pre-process and post-process the color image in the homomorphic system. This method improves the appearance of images as perceived by the human eye, and/or to render these images more suitable for computer analysis. That is, both color rendition and dynamic range compression are achieved using this method.