Wavelet Transform Based Image Compression Method

In the wavelet image compression system,the choice of wavelet basis directly determines the statistical characteristics of wavelet coefficients, thus it not only affects subsequent processes, but also affects the final compression ratio and the the quality of reconstructed image. The method of realizing wavelet transform determines computational complexity, whether the transformed data can be lossless recovered or not, etc., accordingly it can affect the time spending on compression and the quality of reconstructed image.In this paper, the author has performed comprehensive research on the method of wavelet basis selection, wavelet transform realization, wavelet coefficients' optimization, adaptive wavelet's construction, the performance analysis and optimal realization of IWT. The work and innovative results are as follows: 1.Have analyzed principles of image compression, the structure of compression system, methods of evaluating compression system's performance and present methods of image compression. 2.Have summarized the process from continuous wavelet transform to R wavelet transform to gradually eliminate redundancy, the method of constructing biorthogonal and compactly supported wavelets, function's decomposition based on orthogonal or biorthogonal basis, the time-frequency characterization of the first generation wavelet transform and the application of the multi-resolution characterization in image compression.3. Have analyzed and systemically summarized principles and realizing methods of the second generation wavelet, have analyzed advantages of the second generation wavelet transform and their applications in image compression.4.Have analyzed properties of wavelet coefficients obtained from an image through wavelet transform, and discussed how to select wavelet basis to optimize wavelet coefficients.5. Have put forward the idea of constructing adaptive wavelet transform to adapt to an image's local characters, given two methods of constructing adaptive wavelet and analyzed the performance of adaptive wavelets in image compression. Two methods are:a) the method of constructing adaptive predict wavelet.b) the method of constructing adaptive update wavelet.6. Have put forward the idea of introducing smooth process before wavelet transform to weaken an image's local characters. Experiments show the method can optimize wavelet coefficients and increase compression ratio.7. Have analyzed the performance of IWT and reasons resulting in the performance, and put forward two methods to improve its performance inferior to DWT in lossy compression. Two methods area) optimizing factorization to decrease the error of rounding operations.b) amplifying range to avoid the error of rounding operations.