The determining factor in deciding whether to use GIF or JPEG (assuming you
do not need animation) should be the number of colors involved.  GIF's DO
use a very tight compression algorythm, but it is optimized for a lower
number of colors than JPEG is.  GIF is also a LOSSLESS form of compression,
so the quality of your image will never degrade or show "compression noise"
like a JPG will (a "lossy compression").  As a general rule, 25 colors or
less will make a smaller GIF than a JPEG.  If you have a full-color photo,
use JPG.  If it is a simple screen capture or single color bitmap, use GIF.
Dithering also affects the file size of GIF's, so that is another thing to
look at.



>JPG files CAN be significantly smaller than GIFs by working with the
>compression ratio AND the Dots Per Inch.


Actually, DPI has nothing to do with file size.  It is a relitive term that
distainguishes the quality factor of a static-size image.  If used in the
context that a 3x5 image at 300 DPI or a 3x5 image at 600 DPI, obviously the
600 DPI image would br the larger of the two, but this term isn't used for
web graphics at all, only in print media.  (Raster) Web graphics rely simply
on pixel dimensions.

Brad Boutwell
Tulsa, OK

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