- the first graphic file format used on the Web
- two types: 87a (earlier) and 89a (supports transparent colours and animation)
- both use file extension .gif
- 8-bit format, supports a maximum of 256 colours - dithering can give appearance of more colours
- indexed colour, i.e. colours are stored in a table
- uses LZW (Lempel-Zev-Welch) compression, based on repetition of information, so is efficient at compressing rows of identically coloured pixels
- lossless format, i.e. doesn't discard information to save space
- can be interlaced (displays in 4 passes) for progressive download
Note: dithering, interlacing, transparency and animation all increase the size of the file
GIF format is best used for:
- images with large areas of solid colour
- line drawings and charts
- logos, icons, menu buttons, type
- cartoons and illustrations
GIF format should not be used for:
- photographs - compression not good enough
