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From: gbrown@tybalt.caltech.edu (Glenn C. Brown)
Newsgroups: comp.graphics
Subject: Re: Compression of multi-bit images
Message-ID: <1990Jun7.220852.5994@laguna.ccsf.caltech.edu>
Date: 7 Jun 90 22:08:52 GMT
References: <8099@b11.ingr.com> <SPENCER.90Jun4170821@spline.eecs.umich.edu>
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spencer@eecs.umich.edu (Spencer W. Thomas) writes:

>The method currently getting all the noise is DCT (discrete cosine
>transform) encoding.  The idea is to take a "Fourier transform"
>(discrete cosine transform, actually, since the values are all real)
>of little (typically 8x8, I think) blocks of the image.  Only the
>first few coefficients for each block are saved.   

In Scientific American, an short article claimed that some national
committee of something-or-other was trying to set up file standards for
such forms of compression.  They also were able to get reasonable
no-loss compression by Huffman encoding the coefficients.  (I believe
they got about 4:1 with no loss, and could got 11:1 with very little
visible loss of image quality in their 24-bit images.

-Glenn