Studing Of Image Coding Based On Wavelet Transform

Image is the most important information source for human to realize the world because it has very abundant information, but it has great amount of data. With the development of computer networks technology and the multimedia technology, all of these technology call for compressing the great amount of image data. In order to adapt to the practical application, The DCT was used as the main method of image for a long time. But there is obvious "block noise" in using DCT. And it is difficult to improve the compression performance. Wavelet transform becomes the main subject of image compression coding for it has the advantage of describing non-steady signal. This paper focus on the wavelet transforms code.Firstly, this paper analyzes the features of image and the necessary and feasibility for image compression, and makes a comparison and summarizes for the traditional compression methods. Secondly, this paper introduces the basic theory on wavelet transform code EZW and improved algorithm SPIHT and analyzes these two algorithms. From analyses we can know advantages and disadvantages of them. SPIHT uses list structure to keep track of which sets must be tested. During coding, it needs to maintain three lists to store temporarily the image's zero tree structure and significance information. However, the use of lists in SPIHT causes a variable, data dependent memory requirement, and the need for memory management as list nodes are added, removed and moved. At high rate, there can be as many list nodes as coefficients. This may be undesirable in hardware implementation. Thirdly, a developed listless zerotree codec for images and video that makes use of fixed size state tables instead of lists. The amount of memory required by the LZC codec is only a fraction of the amount needed by a SPIHT codec. Consequently the implementation complexity and hardware cost can be reduced significantly. At last, this paper brings forward a design scheme for a real-time compression system based on FPGA and DSP. The scheme takes full advantage of these IC's excellent characters, The scheme have a reasonable data channels of DSP and FPGA, the channels can improve capability of take in and send out in large quantities data of all system. We can find the scheme can finished completely real-time compression based on high-speed from experiments.