packbits

PackBits is a fast, simple compression scheme for run-length encoding of data. Apple introduced the PackBits format with the release of MacPaint on the Macintosh computer. This compression scheme is one of the types of compression that can be used in TIFF-files. A PackBits data stream consists of packets of one byte of header followed by data. The header is a signed byte; the data can be signed, unsigned, or packed (such as MacPaint pixels).

Header byte	Data
0 to 127	1 + `n` literal bytes of data
0 to -127	One byte of data, repeated 1 - `n` times in the decompressed output
-128	No operation

Note that interpreting 0 as positive or negative makes no difference in the output. Runs of two bytes adjacent to non-runs are typically written as literal data.

External links

Apple webpage describing the PackBits format

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