* Posts by David Brown

1 post • joined 27 May 2009

Ocarina makes waves with lossless image compression

David Brown
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Lossless compression using DCT is perfectly possible

It is perfectly possible to use DCTs to make a lossless compression algorithm, even without using very high accuracy DCTs. Nowhere in the article does it say that the compression uses *only* DCTs. First use DCTs to encode a reasonable lossy version of the picture. Then subtract that from the original picture, and you have the high-frequency noise that didn't fit the DCTs. This can be compressed in other ways (there should be very low amplitude in the signals, so you can use only a small number of bits), tied onto the DCT compressed data, and you have a lossless image compression that uses DCTs. In particular, if the "original" image is already a jpeg, the noise difference data should be very small and easily compressed.

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