Re: Image Compression (OH NO!)

[P3D John Ohrt <johrt@xxxxxxx>]

P3D Dylan The Hippy Wabbit wrote:

> Without wanting to get too deep into that can of worms I'd like to know
> what compression algorithm you are referring to.  Most image formats use
> LZW for lossless compression.  With a photograph you are lucky to get any
> compression.  True lossless mode JPEG is a rarely implemented beast, and
> by its designer's admission can only be expected to achieve 50%
> compression.  The 1328 X 728 JPS files you referred to would be about 1.4
> megabytes.  If any one waited long enough for that to download (fat
> chance) they would probably find that they couldn't view it.  Not good PR.
>

Yes, this is a can of worms.

You can view the world of image compression as lossy and lossless.

There are good reasons for lossless compression, particularly that any loss of
quality is unacceptable.  As you have remarked, there are more than one lossless
compression agolrithm, any on real photo quality images the compression
algolrithm may well generate a file larger that the uncompressed data.  This is a
specific problem with .gif and careless use of .tif.

My personal reccommendation is don't use compression.  Failing that, I feel that
zipping or raring the uncompressed file with compression optimization preferred
to some off beat variant of tif.

In my opinion, jpeg is the only worthwile freeware lossy algolritm.  While the
encoder is proprietary, I do like .pcd when a 4:1 compression range is adequate.

With rare exception, I feel all you need are .jpg, .png, and for really precise
data, .fits.

Please note, according to reports Netscape (Win95 for sure) handles .png via a
plugin very elegantly and fast.  As usual, Microsoft IE is out to lunch when it
comes to net standards.

Others may disagree, but that's the way I see it.

Please note that there is the .jps variant of .jpg for stereo and that both .png
and .fits handle multiple images although no header info has been defined to
specify stereo pairs, to my flakey knowledge.

Larry and I might be happy when we can view an 8192x8192x48bit image through our
$99 LCS glasses :-)

Regards,

--

John Ohrt * Toronto * ON * Canada





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