Compression (data)

The temporary coding of data in a way that reduces the file size and saves storage space or transmission time (See also CODEC). Compression is performed by a program that uses a particular algorithm designed to process particular types of data to achieve specific results. There are many different types of programs used in different applications. For example, the compression algorithm used to reduce the size of a text file has very different operating parameters and goals than a program designed to compress audio and video for DVD authoring. One fundamental distinction is whether a particular compression scheme is “lossless” or “lossy.” Compression schemes used for the text files like the one mentioned above are lossless, which means that when the file is decompressed the data can be restored to 100% of its original state. In a lossy compression scheme, such as MPEG video used in DVD production, the quality of the audio and video may be degraded somewhat. Another distinction is whether or not a special decoding algorithm is required to access or uncompress the file. Usually (but certainly not always) lossless compression schemes require special decoding software to restore the file to its original form, whereas lossy compression schemes are often encoded so they can be accessed without the extra decompression step.