几种常见编码方法的比较

Comparison of some commonly used encoding methods

通过对DFT/DCT、子带、小波变换、分形编码的特征分析,得出如下一些结论:DFT与DCT理论成熟,前者因存在复数计算,使得硬件结构较后者复杂,但DCT变换也因分块数限制,在还原图像时可能存在块效应;具有多分辨率分析的小波变换编码,虽然是目前变换编码中较为高级的一种,但也存在选择小波基函数的困难;子带编码具有并行处理和分层传输之优点,但镜像滤波器组的设计难以达到理论要求;根据事物间普遍存在的相似性建立起来的分形编码,以其高压缩比换取图像的极端相似性,失真表现为整个屏幕的随机现象。

The following conclusions are reached on the analysis of DFT,DCT,Subband,Wavelet and Frac-tion coding.Both DFT theory and DCT theory are mature due to the computation of complex number,the former is more complex in hardware structure than the latter.But due to the limit of blocks,DCT transformation may have block effect in restoring the pictures.The wavelet transformation coding with multi-resolution analysis,comparatively su-perior as it is,has difficulty in selecting basic wavelet functions.The subband coding has the advantage of concur-rent processing and stratified transmission,but the design of QMF is not up to theoretical requirements.The frac-tion coding,which is set up on universal similarity,ensures high compression rate and picture signal transmission with various qualities or priorities.The future compression coding must be the fusion of various compression ways.