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Неплохая демонстрация сжатия без потери качества в формате PNG.
http://www.libpng.org/pub/png/img_png/16million.png

Цитата:

By way of example--admittedly an extreme and unrealistic case--a 512 x 32,768 image containing all 16,777,216 possible 24-bit colors compressed over 300 times better with filtering than without. The uncompressed image was 48 MB in size; the compressed-but-unfiltered version was around 36 MB; but the filtered version is only 115,989 bytes (0.1 MB). Yow.

http://www.libpng.org/pub/png/pngintro.html