What is "lossless compression"

Compression \Com*pres"sion\, n. [L. compressio: cf. F. compression.]

1. The act of compressing, or state of being compressed. ``Compression of thought.''
   --Johnson.

2. (Computers) reduction of the space required for storage (of binary data) by an algorithm which converts the data to a smaller number of bits while preserving the information content. The act of compressing [3].

   Note: Compression may be lossless compression, in which all of the information in the original data is preserved, and the original data may be recovered in form identical to its original form; or lossy compression, in which some of the information in the original data is lost, and decompression results in a data form slightly different from the original. Lossy compression is used, for example, to compress audio or video recordings, and sometimes images, where the slight differences in the original data and the data recovered after lossy compression may be imperceptable to the human eye or ear. The JPEG format is produced by a lossy compression algorithm.

Lossless compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data. By contrast, lossy compression permits reconstruction only of an approximation of the original data, though this usually improves compression rates (and therefore reduces file sizes).

Lossless data compression is used in many applications. For example, it is used in the ZIP file format and in the GNU tool gzip. It is also often used as a component within lossy data compression technologies (e.g. lossless mid/side joint stereo preprocessing by the LAME MP3 encoder and other lossy audio encoders).

Lossless compression is used in cases where it is important that the original and the decompressed data be identical, or where deviations from the original data could be deleterious. Typical examples are executable programs, text documents, and source code. Some image file formats, like PNG or GIF, use only lossless compression, while others like TIFF and MNG may use either lossless or lossy methods. Lossless audio formats are most often used for archiving or production purposes, while smaller lossy audio files are typically used on portable players and in other cases where storage space is limited or exact replication of the audio is unnecessary.