Wasn't it Warp who wrote:
>  No-one said that a compression scheme should use just *one* compression
>algorithm.
>  The simples case of using two algorithms is: First try compressing
>with the compression algorithm, and if the result is bigger than the
>original, just store the raw image.
>  This way some of the images will be smaller than the original and some
>will be equal. None of the images will be larger than the original.
>  This way the overall average compression rate will be higher than 1.

The logic still holds. The data plus the information telling you which
decoding system to use must span all possible images, so information
theory strongly suggests that on average you get no compression.

There are some people who dispute this reasoning. For example ZeoSyc
seem to be claiming that they have invented a lossless compression
algorithm that can compress random data by a factor of 100. Their
algorithm is currently secret, pending patent application.

-- 
Mike Williams
Gentleman of Leisure

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