The GIF format

Originally created for CompuServe, this format is compressed without information loss. Another advantage is that you can create animation in this format and make one of the colours in the composition transparent. This can be useful for silhouetting an image.

The drawback is that the GIF format stores only 256 colours. Consequently, the subtle shades of an image are rendered as bands of different densities. Look at the following figure--the image on the left has a gradient using 16.7 millions colours, whereas the one on the right has the same gradient with 256 colours (GIF format).



Figure 2: The 256 colours of the GIF format do not enable a good rendering of gradients.

So, when should you use or not use the GIF format?

• Suitable for buttons and banners (as the typography does not loose its quality), animated GIFs, silhouetting, black and white photos (which usually have 256 grey levels).
  
  
• Not suitable for colour photographs.