19.7 Experiments

All the exploitation-based spectral/spatial compression techniques presented in previous sections are carried out in two stages, that is, VD-determined spectral compression in the first stage followed by either JPEG2000 Multicomponent or 3D-SPIHT spatial compression in the second stage. For the spatial compression, a variable bit-rate lossy compression technique is used in both JPEG2000 Multicomponent and 3D-SPIHT. Since PCA and ICA transforms generate real numbers, we have rounded these numbers to 16 bits in the implementation of spectral/spatial compression techniques. Also, PCA and ICA are data dependent transforms; thus, their component projection vectors need to be stored and/or transmitted in order to perform reconstruction of the data. This factor is considered as an overhead and further included in calculation of compression ratio.

The compression ratios are chosen to be 20, 40, 60, and 100 because little difference is noted in the detection/quantification performance for compression ratios lower than 20. This implies that for very low compression ratios (<10) 3D-cube compression alone and spectral/spatial based compression can successfully preserve the subpixel and mixed pixel information. Such subtle difference can be only observed when the data are compressed with high compression ratios (>40). In order to address the issues of subpixels and mixed pixels, two examples are custom-designed to illustrate and demonstrate the superiority of spectral/spatial ...

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