The Research Of Enhancement Of Color Images In DCT Domain

With the development of the technology in network communication and multimedia, image compression and enhancement become more and more important. Currently, international image/video compression standards (JPEG, MPEG, etc.) which are widely used usually compress and transform images in the form of"block DCT + quantify". Since various coding standards are fixed, the post-processing schemes are used for image/video enhancement. However, the widespread concern about the application currently is the progressive transmission of compressed images. In order to enhance the compressed images fleetly during the process of progressive transmission, the technology of image enhancement in DCT domain has become very imperative. It can eliminate the computational overheads when carrying out the inverse transform to the spatial domain and back into the compressed domain by forward transform.Most image enhancement algorithms are for grayscale images. For color images enhancement, the algorithms are just applied to the three components R, G, B of color images or the brightness component Y. They have not considered the changes of color in the process of image enhancement. The display of a color image depends upon three fundamental factors, its brightness, contrast and color. For preserving the color of image, in the process of image enhancement we should consider not only the brightness component but also the color component at the same time. In this article we will introduce an algorithm that enhances color images by scaling the DCT coefficients (Color Enhancement by Scaling (CES)) and we will implement it by emulation. The algorithm can be simply executed and in the process of image enhancement it can preserve the color well. But we can't receive obvious results while we use the mapping function in the algorithm to deal with the overall darker and low contrast images. In this article we propose a new method, which does not use the mapping function but carry out histogram equalization for the DC image composed of the DC coefficients of each block. The new algorithm can handle the overall darker and low contrast images, improve the effect of enhancement. For the block effect generated by enhancing color images in the block DCT domain, this article offers a simple method of average enhancement factor of the adjacent block to improve the block effect.