Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!uwm.edu!rpi!masscomp!calvin!mark
From: mark@calvin..westford.ccur.com (Mark Thompson)
Newsgroups: comp.sys.amiga
Subject: Re: 24 bit IFF image compression
Message-ID: <61484@masscomp.ccur.com>
Date: 1 Dec 90 15:09:01 GMT
References: <3925@mindlink.UUCP> <1990Nov28.192940.30995@uokmax.ecn.uoknor.edu>
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Reply-To: mark@calvin.westford.ccur.com (Mark Thompson)
Organization: Concurrent Computer Corp. Westford MA.
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In article <1990Nov28.192940.30995@uokmax.ecn.uoknor.edu> drtiller@uokmax.ecn.uoknor.edu (Donald Richard Tillery Jr) writes:
>What we really need is some effective IMAGE compression techniques,
>I have heard of some such algorithms and one type in particular where
>the resulting image IS NOT an exact duplicate of that which started
>out.  But the resulting reduction is up to 90% !  Now if only a .1%
>or less distortion is introduced, I think we can live with that (it
>amounts to about 1 radical pixel every other line) but I don't know
>any specifics about it.

JPEG image compression which has been discussed extensively lately in
some of the other newsgoups and can achieve compression ratios up to 200:1.
However, it is a lossy compression technique which will degrade the
image. For video images, discernable loss begins at about a 20:1
compression ratio (note that the amount of compression performed is user
variable). But remember that video images have half the bandwidth in
color as they do in intensity and intensity is limited to 4.5Mhz. What
this all means is that while this degree of compression is barely noticeable
on a video image, it will be BUTT-UGLY on your gorgeous crisp RGB image.
It is left to be seen how well this compression will fair will a clean
RGB image. Also of note, the compression time can be rather lengthy.
For those interested, the JPEG algorithm uses a discrete cosine transform
followed by quantization (where the loss is incurred) and Huffman encoding.
+--------------------------------------------------------------------------+
|  Mark Thompson                                                           |
|  mark@westford.ccur.com                                                  |
|  ...!{decvax,uunet}!masscomp!mark   Designing high performance graphics  |
|  (508)392-2480                      engines today for a better tomorrow. |
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