Lossy 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.
      [1913 Webster]

   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.
         [PJC]
    

lossy compression \los"sy com*pres"sion\, n. (Computers)
   The compression of binary data into a form which, when it is
   re-expanded, has most, but not all, of the original
   information. It is used primarily for compression of images
   and sounds, and is designed to provide a high degree of
   compression at the cost of a slight loss of data. It is
   expemplified by the JPEG compression standard. Images
   compressed by a lossy compression algorithm are re-expanded
   into an image close, but not identical to the original image;
   the difference between the original and the reconstructed
   image may be imperceptible to normal viewing by the eye.
   [PJC]