Run-Length Encoding

Run-length encoding, or RLE, is a form of lossless data compression in which runs of data, consecutive occurrences of the same data value, are stored as a single occurrence of that value together with a count of its consecutive occurrences, rather than as the original run; for example, a sequence of five consecutive green pixels in an image could be shortened to a note of green repeated five times. It is most efficient on data containing many such runs, such as simple graphic images including icons, line drawings, games and animations, while encoding data without many runs using RLE can actually increase file size. RLE is also the name of particular image formats that use the technique, including an early graphics format supported by CompuServe for compressing black and white images, later widely supplanted by CompuServe's own Graphics Interchange Format, and a little-used Windows 3.x image format saved with the file extension rle that was used for the Windows 3.x startup screen.