Image Compression (OH NO!)

[P3D Dylan The Hippy Wabbit <spacey@xxxxxxxxxxxxx>]

Jon Gross wrote:-

>I suspect that you may not be inclined to publish them with no
>compression because they would be quite large.  And this is my point:
>JPS forces the image authors to choose between size and quality.
>Contrary to popular myth, this is not a required tradeoff.  There do
>exist lossless images compression techniques, which, even though they do
>not achieve the ratios offered by JPEG and others, will maintain high
>image quality with significant space savings for most subject matter.
>(BTW, using PKZIP on a BMP or TIFF image does NOT work well, but that is
>not what I am talking about).

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.

Saving a standard JPG with the compression setting on minimum is still
lossy, and manages quite respectable compression.  You could also go a bit
further and see what you think of the results.

I just tried it.  A 1.5 mb image actually grew when saved as an LZW
compressed TIF, and maximum ZIP compression only cut it down by 4%.  Paint
shop pro V4.12 on it's mimimum jpeg compression managed about 3:1
compression.  No way was that lossless.

Bye Y'all

Dave Spacey

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When you break rules break 'em good and hard.   - Terry Pratchett


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