General Information & References

The GIF file format was originally associated with Compuserve, who wanted a format that would provide universal graphics exchange between the various operating systems. It was designed as a universal standard format for the exchange of graphic documents by the prevalent client platforms using the on-line service.

Unfortunately Compuserve used an algorithm that was patented technology belonging to UNISYS. The LZW algorithm, used in the compression process is based on RLE (Run Length Encoding). For a discussion of RLE see other pages in this document, or the Royal Frazier WEB site. (The Royal Frazier site is an excellent reference for more information on the GIF format and its utilization.) In 1995 UNISYS decided to require a license for use of its patent, with the requirement that commercial applications using LZW compression pay for that right. Programs which "display only" are apparently not required to pay for the right to interpret the file. This gave rise to a potential new format called the "PNG" (Potable Network Graphics) format. It is not yet widely accepted by the major browser companies, and has been slow in implementation. It does not support muti-images per file, hence no animation.

GIF files have two important dates associated with their format definition. 1987 and 1989 are the key dates, and the formats are, incidentally, called the 87a and 89a formats. The 87a format provided for the LZW compression, and the incorporation of multiple images within a single file. In the 89a version they added transparency, delay factors between images, disposal methods, and the ability to add application specific code to the file format. NetScape was an early adopter of this by adding the ability to loop an image.

GIF General:

8 bit color (or less) A good tutorial on color can be found at "Cyberglitz."
no practical size limitations
transparent color available
multi-images in one file
time delay between images
disposal methods after image display
internal coordinate system for translation
looping (thank you NetScape)

These are the GIF features that most WEB authors use in creating graphic images for WEB page use. These features and how they relate to color palette selection, dithering, gradations, animation, and browser viewing are the topics covered in this "GIFOLOGY."

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