Re: How much lossless compression is possible in images?

From: HERC777 (herc777_at_hotmail.com)
Date: 12/07/04 

Date: 6 Dec 2004 20:57:13 -0800

The point here is any compression algorithm, or system of compression
algorithms,
operating on the total set of inputs, cannot get a total compression
over the entire set.

Consider 2MB 1000 pixels X 1000 pixels

Raw Data "Compressed File"
1 66
2 44
3 2
4 1
5 ..
..
16^1,000,000

There are 16^1,000,000 possible picture files, so there must be
16^1,000,000 distinct compressed files.

You can't have 16^1,000,000 distinct files unless the average file
length is over 1MB.
The average file length of the original 16^1,000,000 images is also
1MB.

Therefore, not every picture gets compressed.

Finding a particular compression algorithm for that image doesn't help
in the global scheme of things, because you have to say what the
algorithm is, and it wont be small. The length of the algorithm + the
compressed file will tend to be larger than the original file. The
exceptions are easily compressible data, lots of flat areas.

Herc

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