Run-length encoding

Not to be confused with Run-length limited.

Run-length encoding (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 data value and a count of its consecutive occurrences, rather than as the original run. For example, a sequence of "green green green green green" in an image built up from colored dots could be shortened to "green x 5".

Run-length encoding is most efficient on data that contains many such runs, for example, simple graphic images such as icons, line drawings, games, and animations. For files that do not have many runs, encoding them with RLE could increase the file size.

RLE may also refer to particular image formats that use the encoding. RLE is an early graphics file format supported by CompuServe for compressing black and white images, that was widely supplanted by their later Graphics Interchange Format (GIF). It is also the name of a little-used image format in Windows 3.x that is saved with the file extension rle, consisting of a run-length encoded bitmap; it was used as the format for the Windows 3.x startup screen.

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