HTML and CSS Reference
In-Depth Information
tools now save your creations or acquired images in GIF format, and
most now let you enable transparency and make interlaced GIF files.
There also are a slew of shareware and freeware programs specialized
for these tasks, as well as for creating GIF animations. Look into your fa-
vorite Internet software archives for GIF graphics and conversion tools,
and see
Chapter 17
for details on creating transparent images.
5.2.1.3. JPEG
The Joint Photographic Experts Group (JPEG) is a standards body that
developed what is now known as the JPEG image-encoding format.
Like GIFs, JPEG images are platform independent and specially com-
pressed for high-speed transfer via digital communication technologies.
Unlike GIF, JPEG supports tens of thousands of colors for more detailed,
photorealistic digital images. And JPEG uses special algorithms that yield
much higher data-compression ratios. It is not uncommon, for example,
for a 200 KB GIF image to be reduced to a 30 KB JPEG image. To achieve
that amazing compression, JPEG does lose some image data. However,
you can adjust the degree of "lossiness" with special JPEG tools so that
although the uncompressed image may not exactly match the original,
it will be close enough that most people cannot tell the difference.
Although JPEG is an excellent choice for photographs, it's not a partic-
ularly good choice for illustrations. The algorithms used for compress-
ing and uncompressing the image leave noticeable artifacts when deal-
ing with large areas of one color. Therefore, if you're trying to display a
drawing, the GIF format may be preferable.
The JPEG format, usually designated by the
.jpg
(or
.JPG
) filename suf-
fix, is nearly universally understood by today's graphical browsers. On
rare occasions, you'll come across an older browser that cannot directly
display JPEG images.
