The Research On Image Compression Coding Algorithm Based On Wavelet Transform

Into the 21st century, mankind has entered an era of information, image information becomes an important origin of obtaining information from outside. But the data quantity of image is huge, which not only requires high storing and operating capacity for computers, but also restricts the channel transfer rate of image communication. Therefore, in order to store, process and transfer the data, compress processing must be done for image information. Wavelet transform has wonderful space and frequency features, so it can deal with the image effectively. This thesis mainly researches the image compression coding algorithm that is based on the wavelet transform:Firstly, it introduces the basic theory of wavelet transform in details, the emphases of this part is the energy changes and the distribution characteristics of the coefficients before and after the wavelet transform, and then the reasonable basis that wavelet transform in favor of image compression is found.Secondly, on the basis of above, two kinds of zerotree coding algorithms that are based on the wavelet transform are researched and simulated. And EZW is a simple and effective image coding algorithm, the wavelet transform coefficients of all sub-bands are expressed as the zerotree structure, an encoder can terminate the encoding at any point, so allow achieving a precise rate or distortion.Thirdly, some improvements have been made by researching on the basis of above algorithms. The improved algorithm from constructing the wavelet filters, selecting the appropriate predictor to deal with the most low-frequency sub-band separately by calculating the local metric△h and△v of the direction properties of an image, using the "zerotree maximum table"' on other high-frequency sub-band . to position scanning and quantize the coefficients in a more effective way. The simulation results show that the improved algorithm has shortened the encoding time significantly, and the image quality and compression ratio is unchanged basically.Finally, this thesis summarized the work done and pointed out the problems in the improved algorithm then prospected the orientation that can continue to make in-depth study in the image compression coding algorithm in the future which is based on wavelet transform.