JPEG Image compression

Subject: JPEG Image compression
From: Steve Fouts <sfouts -at- ELLISON -dot- SC -dot- TI -dot- COM>
Date: Mon, 19 Dec 1994 14:32:43 CST

Arlen Walker writes:

|} JPEG (Joint Photographic Experts Group) is a releatively new standard for
|} image compression which works astoundingly well. It can achieve 10:1 or
|} better compression of images. Be advised this is a "lossy" compression
|} scheme. (It removes detail in areas of the image where it judges detail
|} to not be important. Yes, that's right, it irrevocably throws away some
|} of the image it compresses. Before you scream, try it on a few images.
|} I've loaded several "before & after" images into Photoshop, and I've
|} rarely been able to spot the "lost" detail. And even then it wasn't
|} important.)

Just thought that I would add that JPEG compression gives you the
ability to decide between detail and image size. Suppose you scan
in a still life with roses as a 24-bit TIFF (Tagged Image File Format),
then convert it to 24-bit JPEG. The best you can do with JPEG is about
95% of the original TIFF's quality, but it will be a MUCH smaller file.
From you can crank down the compression until you have a blurry mess
with about 5% of the original image quality in an exceedingly tiny
place, if you wish.

One caveat to JPEG. It was created for photographs. It tends to lose
text fairly quickly as you slide up the compression scale, so if your
picture has text in it, go for maximum picture quality. It will still
be smaller than the TIFF that spawned it.

_______________ _____
/ ___ __/__\ \ / / _\ Steve Fouts
/___ \| | ___\ | / __\ sfouts -at- ellison -dot- sc -dot- ti -dot- com
/ / \ | \ / \
/_______/__|_______\_/________\ "She understood, as he did, that all writing
was infernally boring and futile, but that it had to be done out of respect
for tradition" --Stanislaw Lem

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