Multispectral Image Compression Using Wavelet Transform

研究了七波段陆地卫星专题图像的高效有损图像压缩方法。利用包括Kahoku湖在内的金泽市北部地区的图像进行了测试。1.3维DCT和标量/矢量量化去除了6波段图像，其他6个波段图像中的像素之间的相关性被3-D DCT去除了。6波段图像是单独压缩的，因为它在空间分辨率上与其他波段图像有很大的差别。DCT系数表示为F(i，j，k)，其中i：水平8阶，j：垂直8阶，k：频带方向6阶变量。由于具有相同i、j和k的系数的方差相对较小，因此将它们合并成一个块，在DC块中对系数进行DPCM熵编码。根据i+j+k的大小将其他块分为5组(G)，对G1-G3进行标量量化和熵编码，对G4进行大小为1*4的矢量量化，对G5进行丢弃，根据丢弃的小功率向量数量与总向量数量的比例调整比特率。在码率大于1.2bpp的情况下，峰值信噪比大于32db。2.小波变换和带间差分编码对带2的图像进行两级小波变换和方向矢量量化。然后对其他频带图像和重建的频带2图像之间的差值图像进行三维DPCM标量和矢量量化，其结果是在1.2bpp~1.6bpp的码率下，峰值信噪比比三维DCT1.2~1.6bpp的峰值信噪比高0.3db。发展了3.2-CH完全重构IIR滤波器Banka滤波器组，使得所有的分析和合成滤波器都具有线性相位，并且近似满足功率互补条件。

High efficiency lossy image comression is investigated for seven band Landsat Thematic Mapper imagery. The image of north part of Kanazawa city including Kahoku lake is used for testing.1.3-D DCT and scalar/vector quantizationRemoving Band 6 image, inter-and inter-band correlation between pixels in other 6 band images is removed by 3-D DCT.Band 6 image is solely compressed, because it differs greatly from other band images in spatial resolution. DCT coefficients are denoted F (i, j, k) where i : horizontal 8th order, j : vertical 8th order and k : band directional 6th order variables. As the coefficients with the same i, j and k has relatively small variance, they are united to form a block.In the DC block, the coefficients are DPCM-entropy coded. The other blocks are classified into 5 groups (G) according to the value of i+j+k. G1-G3 are scalar quantized and entropy coded, G4 is vector quantized with size of 1*4 and G5 is discarded.Bit-rate is abjusted by the ratio of the number of discarded small power vectors to the total number of vectors. In bit-rate greater than 1.2 bpp, PSNR greater than 32 dB is obtained.2.Wavelet transform and interband differential codingThe image of band 2 is two stage wavelet transformed and directionally vector quantized. Then differential pictures between the other band image and the reconstructed band 2 image are 3-D DPCM-scalar and vector quantized in the similar way to section l. As a result, 0.3 dB higher PSNR is obtained in the bit-rate of 1.2-1.6 bpp compared with those of 3-D DCT.3.2-CH perfect reconstruction IIR filter bankA filter bank system is developed such that all the analysis and Synthesis filters have linear phase and satisfy the power complementary condition approximately.