JGP compression for WEB posts

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Sat, 20 Sep 1997
>From: P3D Ralph Johnston writes:
>....................
>Last night I saved another image with compressions ranging from 2 to 256
>and examined them.  It turned out that only above 180 could I tell any
>difference.  I settled on 128.  Below are the sizes vs compression number:
>................
>Based on the above I am going to resample it at 800 pixels wide and use 128
>compression.
>

Most programs with sliding scales for JPG use a 0 to 100 scale, not that
that should make much difference as long as one does similar testing to see
what you like. However, I would caution you to not assume that all images
will work at the same numbers that you concluded from your test.

Due to how JPG works, different image types are affected adversely to
different degrees. I've seen some images I could compress at very high rates
and not be able to tell a difference, while certain others seem to show
image degredation at low percentages of around 35%. Learn to recognize which
images might have a problem and test them individually.

Then as others have pointed out, not all programs that provide JPG do it
equally well. Test and compare between whatever programs you have available
so you know your own tools relative to each other.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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