Page "Data compression" Paragraph 5

Lossless data compression algorithms usually exploit statistical redundancy to represent data more concisely without losing information.

Lossless compression is possible because most real-world data has statistical redundancy.

For example, an image may have areas of colour that do not change over several pixels ; instead of coding " red pixel, red pixel, ..." the data may be encoded as " 279 red pixels ".

This is a simple example of run-length encoding ; there are many schemes to reduce size by eliminating redundancy.