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Proceedings Paper

Improving a DWT-based compression algorithm for high image-quality requirement of satellite images
Author(s): Carole Thiebaut; Christophe Latry; Roberto Camarero; Grégory Cazanave
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Paper Abstract

Past and current optical Earth observation systems designed by CNES are using a fixed-rate data compression processing performed at a high-rate in a pushbroom mode (also called scan-based mode). This process generates fixed-length data to the mass memory and data downlink is performed at a fixed rate too. Because of on-board memory limitations and high data rate processing needs, the rate allocation procedure is performed over a small image area called a "segment". For both PLEIADES compression algorithm and CCSDS Image Data Compression recommendation, this rate allocation is realised by truncating to the desired rate a hierarchical bitstream of coded and quantized wavelet coefficients for each segment. Because the quantisation induced by truncation of the bit planes description is the same for the whole segment, some parts of the segment have a poor image quality. These artefacts generally occur in low energy areas within a segment of higher level of energy. In order to locally correct these areas, CNES has studied "exceptional processing" targeted for DWT-based compression algorithms. According to a criteria computed for each part of the segment (called block), the wavelet coefficients can be amplified before bit-plane encoding. As usual Region of Interest handling, these multiplied coefficients will be processed earlier by the encoder than in the nominal case (without exceptional processing). The image quality improvement brought by the exceptional processing has been confirmed by visual image analysis and fidelity criteria. The complexity of the proposed improvement for on-board application has also been analysed.

Paper Details

Date Published: 17 September 2011
PDF: 13 pages
Proc. SPIE 8157, Satellite Data Compression, Communications, and Processing VII, 815702 (17 September 2011); doi: 10.1117/12.892528
Show Author Affiliations
Carole Thiebaut, CNES (France)
Christophe Latry, CNES (France)
Roberto Camarero, CNES (France)
Grégory Cazanave, Magellium (France)


Published in SPIE Proceedings Vol. 8157:
Satellite Data Compression, Communications, and Processing VII
Bormin Huang; Antonio J. Plaza; Carole Thiebaut, Editor(s)

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