Mike Williams <mik### [at] nospamplease> wrote:
> 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.

  In fact, every image file has to contain at least the information about
its dimensions. Generally at least 4 bytes are used to define the dimensions
of the image.
  Besides this, it usually contains information about the pixel depth (ie.
how many bits per pixel it has).
  This means that taking every possible image (ie. every possible pixel
combination), on average you get a *bigger* file than the plain raw image.

  The *only* way of getting an average of no compression is that we only
use fixed-sized images with fixed-sized pixel depth.
  But in this case the size of the file itself is the piece of information we
need to know if the compression algorithm was used or if the image is raw:
If the size of the file is exactly what is needed to contain the raw image
data, then compression was not used. If the size of the file is smaller, then
compression was used.
  In this case we get an average file size which is smaller than the original
file size.

> 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.

  I think this is theoretically impossible, as shown in this thread.

  Of course if they say that *some* images can be compressed by a factor of
100, then it's believable. However, it's nothing fancy: Just take a huge
image with one color and compress it with whatever algorithm you like. You
can easily get a compression factor of 100000:1 if you want.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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