Ratio rule and homomorphic filter for enhancement of digital colour image

Digital colour image enhancement using a homomorphic filter provides good dynamic range compression, but it fails in colour rendition. In this letter, we propose to perform natural colour rendition in a digital colour image that is enhanced by a homomorphic filter. A novel neural network learning algorithm, named Ratio rule, is used to carry out the natural colour rendition process. The Ratio rule learns to restore colour in an image by representing the colour relationships of each pixel in the original image as a line of attraction in the state space. The dynamics of the neural network is then used as an associative memory for recalling the natural colour characteristics of image pixels after homomorphic filtering. Several experiments on benchmark problems show that the new technique of image enhancement can generate natural colour in images from their original colour information.