Graphics Formats for the WWW: GIF
GIF is a proprietary specification of Compuserve Information Services.
GIF was introduced by CompuServe, and stands for
Graphics Interchange Format.
It was intended to be a platform-independent format with which users
could transfer files over modem lines at low speeds.
Filenames typically end in .gif
It's a compressed format with 1 to 256 colors (8-bit).
Typically the compression is 3:1 to 5:1.
There are two standards: 87a, 89a (transparency).
It allows 1 bit transparency (a pixel is either transparent or opaque).
It allows a palette of a maximum of 256 colors, so representation
of 24 bit color images in GIF involves loss.
It supports interlaced images:
every 8th row in an image is displayed first,
then every fourth, then every second...
Interlacing was invented to allow users to visualize images
being downloaded over slow modems.
Most graphics programs can read interlaced GIFs but might not
be able to create or write them.
Transparency allows a color to be specified as "see-through".
Most browsers should recognise transparent GIFs.
You can use them as spacers, fonts, and various other effects.
At the end of December 1994 Unisys announced that they would be suing
for patent fees for all developers of GIF software, because of GIF's
use of proprietory LZW compression.
GIF has been used very extensively and is available in all browsers
which can handle graphics.
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