| 摘要 |
A method of scrambling a compressed audio and/or picture signal to provide a scrambled signal for distribution, the information content being recoverable from the scrambled signal using descrambling means (10) under the control of authorised recipients of the scrambled signal, is described. The method consists of or includes: a) encoding the information content using a wavelet filterbank having a tree structure; b) distributing the scrambled signal to authorised recipients; and c) decoding the information content using the corresponding inverse wavelet filterbank. The wavelet filter used, the wavelet filterbank tree structure, the number of decomposition stages in the tree structure and/or the time for which a given filter or tree structure or number of decomposition stages is used can be changed in an apparently random fashion to improve security whilst keeping the scrambled signal recognisable. Progressively increasing distortion with time is also described.
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