HTML and CSS Reference
In-Depth Information
several features that make it popular for use in HTML and XHTML doc-
uments. Its encoding is cross-platform so that with appropriate GIF-de-
coding software (included with most browsers), the graphics you create
and make into a GIF file on a Macintosh, for example, can be loaded in-
to a Windows-based PC, decoded, and viewed without a lot of fuss. The
second main feature is that GIF uses special compression technology
that can significantly reduce the size of the image file for faster transfer
over a network. GIF compression is "lossless," too; none of an image's
original data is altered or deleted, so the uncompressed and decoded
image exactly matches its original. Also, GIF images can be easily an-
Even though GIF image files invariably have the .gif (or .GIF ) filename
suffix, there actually are two GIF versions: the original GIF87 and an
expanded GIF89a, which supports several new featuresincluding trans-
parent backgrounds, interlaced storage, and animationthat are popular
with web authors (see section ). The currently popular browsers
support both GIF versions, which use the same encoding scheme that
maps 8-bit pixel values to a color table, for a maximum of 256 colors per
image. Most GIF images have even fewer colors; there are special tools
to simplify the colors in more elaborate graphics. By simplifying the GIF
images, you create a smaller color map and enhance pixel redundancy
for better file compression and, consequently, faster downloading.
However, because of the limited number of colors, a GIF-encoded image
is not always appropriate, particularly for photorealistic pictures (see the
discussion in section ). GIFs make excellent icons, reduced-color
images, and drawings.
Because most graphical browsers explicitly support the GIF format, it is
currently the most widely accepted image-encoding format on the Web.
It is acceptable for both inline images and externally linked ones. When
in doubt as to which image format to use, choose GIF. [*] It will work in
almost any situation.
[*] We cannot resist the temptation to point out that choosy authors choose GIF.
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