PackBits

Overview
PackBits, or Apple Macintosh PackBits, is a simple lossless image compression scheme that uses run-length encoding.

It is byte-oriented (as opposed to pixel-oriented), so depending on how the image data is organized, it may be ineffective for images that use more than one byte per pixel.

Related formats
PackBits compression is used by MacPaint files, and some TIFF files.

Specifications

 * TIFF 6.0 Specification, Section 9: PackBits Compression
 * Technical Note TN1023: Understanding PackBits

Resources

 * Wikipedia article