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Image File Formats for the Web

  GIF JPEG/JPG PNG
Full name Graphics Interchange Format Joint Photographic Experts Group Portable Network Graphics
File name extension .gif .jpeg or .jpg .png
Browser support excellent excellent very good (IE6 problems)
Animation yes no no
Transparency* yes (fixed) no yes (variable)
Compression** lossless lossy lossless
Maximum number
of colors
256 millions 256 (PNG-8 format)
millions (PNG-24 format)
Primary use line art, logos, flat color photographs, continous tone line art, logos, flat color
Open standard no, but patent expired yes yes
Intended output screen screen or print screen or print

* Transparency: With GIF, a pixel is either fully transparent or it's opaque. With PNG a pixel can be partially transparent (although some old browsers don't properly support this PNG feature).

** Compression: Because of "lossy" compression, every time a JPEG is saved some information and quality is lost.