Dictionary: compression   (kəm-prĕsh'ən)

1. 1. The act or process of compressing.
   2. The state of being compressed.
2. 1. The process by which the working substance in a heat engine, such as the vapor mixture in the cylinder of an internal-combustion engine, is compressed.
   2. The engine cycle during which this process occurs.
3. Computer Science. The process by which data is compressed into a form that minimizes the space required to store or transmit it.

noun

A compressing of something: constriction, squeeze. See tighten/loosen.

The act of pressing together or forcing into less space.

1. The state of being compressed, or being shortened by a force.
2. The change in length produced in a test specimen by a compressive load.

Compression, a digital process that allows data to be stored or transmitted using a reduced number of bits. It can be lossless or ‘lossy’. The simplest type of lossless compression stores only the data that change from one pixel to the next. Thus a scene of uniform tone and colour takes up less memory than than a complex scene containing a wealth of detail. A more sophisticated system, LZW, also encodes any patterns repeated within the image, and is incorporated in the TIFF (Tagged Image File Format) and GIF formats. The popular compression routine JPEG is a lossy system that separates luminance and chrominance (as does a television signal) and applies lossy compression, the amount determined by the user, to the chrominance signal. The amount of data loss tolerable depends on the desired final use of the image.

— Graham SaxbyGraham Saxby

Bibliography

• Tarrant, J., Digital Camera Techniques (2003)

A force squashing, squeezing, or pressing down on an object. The distribution of compression within an object is called compressive stress and is measured as the compression force applied per unit area of the object being squashed. Compression tends to change the shape of an object and reduce its volume. See also Poisson effect. Compare shear force: tension.

1. the act of pressing upon or together; the state of being pressed together. A specific example is compression plating in fracture repair.
2. in embryology, the shortening or omission of certain developmental stages.
3. see data compression.

Compression screws used in fracture repair in horses. By permission from Hinchcliff KW, Kaneps AJ, Equine Sports Medicine and Surgery, Saunders, 2004

• c. band — pulled tightly across an animal on an x-ray table to reduce thickness, restrict respiratory movement and restrain the patient. Both ends of the band are fixed to the table and there is a mechanism for tightening it. May be used to apply pressure to an organ such as the urinary bladder to impede filling with excreted dye, but in other applications has the disadvantage of distorting organs and their disposition.
• c./distraction methods — a stress-radiographic method of positioning dogs for the assessment of hip laxity for the diagnosis of hip dysplasia. One radiograph is taken with the femoral heads compressed into the acetabula. The other position is with maximal lateral displacement of the femoral heads using a special device for leverage.
• hourglass c. — in wobbler syndrome of Great Dane dogs, characteristic compression of the cervical spinal cord caused by hypertrophy of the annulus fibrosus, hypertrophy of the ligamentum flavum and degenerative disease of articular facets.
• c. plating — an internal fixation method of treating fractures by the application of plates across the fracture lines and fixing them in place with specially designed screws. The objective is to provide extreme stability of the fracture. Properly designed plates of the correct size for the patient and the use of screws with maximum holding power make the system independent of any additional form of support.
• c. plating device — a device that is connected to an already fixed end of a compression plate and then connected to the other bone fragment so as to obtain as complete compression as possible. Not commonly used when modern dynamic compression plates are utilized.
• spinal cord c. — compression of the cord by a space-occupying lesion in the vertebral canal causes an upper motor neuron syndrome below and a lower motor neuron syndrome at the site of the lesion.

Compression itself may refer to:

• Gas compression, raising the pressure and reducing the volume of gases
• Physical compression, the result of the subjection of a material to compressive stress
• Compression arch suspended-deck bridge, a compression arch rises above the deck
• Compression (geology), a system of forces that tend to decrease the volume of or shorten rocks.
• Compression in zoology and paleontology refers to where an animal, or part of an animal is shorter or narrower compared with other animals in the same group; eg the body of a lizard may be compressed (flattened) so it can better fit into crevices under rocks.
• Compression ratio, a number that predicts the performance of any internal-combustion engine
• Data compression, encoding information using fewer bits
  • Image compression
  • Audio data compression
  • Video compression
    • Compression artifact, noticeable defects in audio or video that has been compressed
  • Bandwidth compression, in telecommunications
• Gain compression in electronic amplifiers, which is a result of device non-linearity
• Audio level compression, usually artificially introduced Gain compression to improve the perceived quality of audio
• Compression (functional analysis), in mathematics
• Compression bandage, designed to reduce the flow of blood
• Compression, the opposite of Tension.

Compressibility also has the special meanings:

• Compressibility, a measure of volume change resulting from pressure (typically for fluids)
• Reciprocal of the bulk modulus (typically for solids)

See also

• Gas compressor
• Compressor
• Compressor (software), Final Cut video and audio compression and encoding application
• compress, a UNIX program
• KOMPRESSOR, an electronic musician.
• Compaction
• Decompression
• Expansion

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Dansk (Danish)
n. - kompression, sammenpresning

Nederlands (Dutch)
compressie

Français (French)
n. - (gén, Phys) compression, réduction, (Comput) condensation, compression

Deutsch (German)
n. - Verdichtung, Kompression

Ελληνική (Greek)
n. - συμπίεση, σύνθλιψη

Italiano (Italian)
compressione

Português (Portuguese)
n. - compressão (f), redução (f)

Русский (Russian)
сжимание, компрессия

Español (Spanish)
n. - compresión

Svenska (Swedish)
n. - sammantryckning, press, kompression (tekn.)

中文（简体） (Chinese (Simplified))
浓缩, 压榨, 压缩

中文（繁體） (Chinese (Traditional))
n. - 濃縮, 壓榨, 壓縮

한국어 (Korean)
n. - 압축하다, 간결한, 압박증

日本語 (Japanese)
n. - 圧縮, 圧搾, 要約

العربيه (Arabic)
‏(الاسم) ضغط, كبس, انضغاط‏

עברית (Hebrew)
n. - ‮לחיצה, דחיסה‬

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