Editing Lossless compression (section)

{{short description|Data compression approach allowing perfect reconstruction of the original data}}
{{Use mdy dates|date=August 2021}}

'''Lossless compression''' is a class of [[data compression]] that allows the original data to be perfectly reconstructed from the compressed data with no loss of [[information]]. Lossless compression is possible because most real-world data exhibits [[Redundancy (information theory)|statistical redundancy]].<ref>{{Cite web |title=Unit 4 Lab 4: Data Representation and Compression, Page 6 |url=https://bjc.edc.org/bjc-r/cur/programming/4-internet/4-representation-compression/6-compression.html?topic=nyc_bjc/4-internet.topic&course=bjc4nyc.html&novideo&noassignment#:~:text=Lossless%20compression%20works%20by%20removing,an%20example%20of%20lossless%20compression. |access-date=2022-04-09 |website=bjc.edc.org}}</ref>  By contrast, [[lossy compression]] permits reconstruction only of an approximation of the original [[data]], though usually with greatly improved [[Bit rate#Bitrates in multimedia|compression rates]] (and therefore reduced media sizes).

By operation of the [[pigeonhole principle]], no lossless compression algorithm can shrink the size of all possible data: Some data will get longer by at least one symbol or bit.

Compression algorithms are usually effective for human- and machine-readable documents and cannot shrink the size of [[random]] data that contain no [[Redundancy (information theory)|redundancy]]. Different algorithms exist that are designed either with a specific type of input data in mind or with specific assumptions about what kinds of redundancy the uncompressed data are likely to contain.

Lossless data compression is used in many applications. For example, it is used in the [[ZIP (file format)|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 [[Joint encoding#M/S stereo coding|mid/side joint stereo]] preprocessing by [[MP3]] encoders and other lossy audio encoders).<ref>{{cite news |last1=Price |first1=Andy |title=Lossless Streaming – the future of high res audio |url=https://audiomediainternational.com/lossless-streaming-back-to-the-future/ |work=Audio Media International |date=3 March 2022}}</ref>

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 would be unfavourable. Common 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 [[Multiple-image Network Graphics|MNG]] may use either lossless or lossy methods. [[Audio compression (data)#Lossless|Lossless audio]] formats are most often used for archiving or production purposes, while smaller [[Audio compression (data)#Lossy audio compression|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.