Wavelet-Based Multidirectional Transform And It's Application To Image Compression

Recently, the amount of image data increase quickly, this brings some problems for data storage and transport. Thus it's very necessary to compress the image in order to decrease the data amount. In image compression, we focus on how to reconstruct the original image with least distortion, especially on the retain of textures and contours. But the traditional algorithms include the most popular image coding algorithms based on wavelet can not restore the detailed texture information which has distinct directional property very effectively. The multiresolution geometry analysis (MGA) developed in recent years is the best sparse signal expression method, it has a good detect ability for the lines and curves in high dimensional space. It takes advantage of the image's geometry property, and provides new ways for image compression.This paper first starts with the popular MGA tools-contourlet transform, itsconstruct procedure will be discussed. Contourlet transform combines the multiresolution decomposition function of laplacian filters and the multidirection decomposition function of directional filter banks. The experiment results show that contourlet transform has good nonlinear approach ability, but its redundancy is a block for image compression. Thus takes the DFB as a tie and combines with the wavelet transform theory, this paper proposes two kind of compression encode methods for wavelet based directional transform. To overcome the redundancy of contourlet, we discard the laplacian pyramid filter banks which could induce redundancy. By using the wavelet for multiresolution decomposition and then add DFB to high frequency subbands for directional decomposition, the wavelet based contourlet transform (WBCT) is implemented. Accordingly the WBCT-based SPITH compression coding method is proposed, the experiment results prove that the method can identify the image directional character much better, and restore more textures. Since WBCT can bring artifacts to the smooth area of an image, it is optimized by...