At 02:27 PM 1/8/2002 -0700, Michael Motyka wrote: >[EMAIL PROTECTED] wrote : > > > >On 8 Jan 2002, at 9:51, Michael Motyka wrote: > > > >> Eric Cordian <[EMAIL PROTECTED]> wrote : > >> >Someone else needs to read the comp.compression FAQ.
>What exactly is random data? Does it have to appear to be random? Does >it have to pass some set of statistical tests to be random? If a string >or bits from a radiation source spells "Merry Christmas and a Happy New >Year" in ASCII is it non-random - a message from above? If a string of >bits from a natural source ( decay etc ) matches a string of bits from >some PRNG is it somehow disqualified as truly random data? > >I think the classification random does not rule out the presence of >local patterns however obscure. If a substring of data happens to match >what is generated by some PRNG then that substring can be "compressed" >to {generator, seed, count}. The geological timescale might be involved >in matching generator outputs to input data sections or deriving >generators for subsections of data. I came up with a similar approach in the late '80s (I may have even discussed it on the list a year or so back). I was interested in compressing image data, which has quite a bit of inter-pixel correlation. My approach was to run a Hilbert space filling curve through the image (it looks like a tightly wound maze). This allows one to maintain most of the pixel correlation while transforming from an array to line. Then I analyzed the auto correlation of the runs of various lengths and attempted to create generators which could produce the required combinations/permutations and auto correlations to code for the runs. I say attempted, because I was never able to find acceptable algorithms to satisfy my requirement. I still believe these algorithms exist, it was just my limitations in identifying the underlying math needed. steve