Adaptive channel error protection of subband encoded images |
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Authors: | Westerink PH Weber JH Boekee DE Limpers JW |
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Affiliation: | Matsushita Appl. Res. Lab., Burlington, NJ; |
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Abstract: | Protection of images that are encoded using subband coding from channel error is addressed. In this scheme the low-pass subband is encoded using DPCM (differential pulse-code modulation), and the other subbands are encoded using a scalar quantizer. The quantizers are all Lloyd-Max quantizers, from which the representation levels have fixed length codewords. First, considering only single errors in each codeword, a channel error distortion measure is derived for each quantizer, that is, for each subband. Codewords are assigned to the quantizer representation levels, yielding a low value of the distortion measure. Next, sets Sij consisting of the jth bit from subband i are formed. Each set S ij is assigned a particular BCH code Cij. An algorithm that optimally assigns BCH codes Cij to each set Sij, based on a channel error distortion measure for the entire image, is derived. The protection scheme is adaptive, because each set of bits within each subband can be assigned a different error protection code. Examples show that this approach is preferable to assigning equal error protection codes to each set of bits. It is shown that in the case of a channel error probability of 10 -3, only 5% to 10% extra bits are needed for adequate channel error protection |
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