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Bytes for Beginners.

I'm starting to work with my students as they build pages for our school's Web site. But I'm confused by one thing--graphics! What's the difference between GIF and JPG?

You need a clear picture of the difference between the two graphic formats if you want to build attractive, fast-loading Web pages.

Both GIF (Graphics Interchange Format) and JPG (Joint Photographic Experts Group) are compressed graphic formats. They use different algorithms to shrink the size of the original graphic file.

GIF is referred to as a "lossless" compression format because when it shrinks a graphic, it remembers what data it removed from the original graphic file and adds it back whenever the file is redisplayed.

JPG (pronounced "jay peg") is "lossy," meaning that the decompressed image isn't quite the same as the one you started with. JPG is capable of achieving much greater compression than is possible with GIF.

JPG is superior to GIF for storing full-color or gray-scale images of "realistic" scenes--scanned photographs, continuous-tone artwork, etc. Any smooth variation in color, such as occurs in high-lighted or shaded areas, will be represented more faithfully and in less space by JPG than by GIF.

GIF does significantly better on images with only a few distinct colors, such as line drawings and simple cartoons.

Large areas of an image that are all exactly the same color are compressed efficiently by GIF. JPG can't squeeze such data without introducing visible defects.

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Publication:NEA Today
Geographic Code:1USA
Date:May 1, 2000
Words:238
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