BEAR image compression

BEAR image compression was used on the Amiga and Acorn Archimedes computers. It was designed for continious tone images in 16 levels of grey. It gives better compression ratio than GIF and is very simple to implement. The small differences between pixels is coded with short symbols, large differences are coded with 7 bits and loads the absolute value of the pixel.

  0 - No change
 10 - Decrease brightness
110 - Increase brightness
111 xxxx - Set pixel

Any code that could be replaced by a shorter code or would go outside the range of 0-15 is reserved. These codes were supposed to be used for run-length encoding but this was never implemented.

This algorithm could be run efficiently on the ARM CPU in the Archimedes but it was slow on the MC68000 CPU in the Amiga.