compression

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noun

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

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.

The act of pressing together or forcing into less space.

• Processes, Phenomena, Events, and Techniques - compression: stress force squeezing crustal rock together
• Principles of Mechanics, Waves, and Measurement - compression: reduction in volume of substance due to pressure
• Software, Languages, and Programming - compression: programming technique that compacts large amounts of data for storage on disks or inclusion in program
• Internal Combustion Engine - compression: reduction in combustion chamber volume prior to power stroke on ignition

Look up compression or compressor in Wiktionary, the free dictionary.

Compression may refer to:

In physical science

• Compression (physical), the result of the subjection of a material to compressive stress
• Compression member, a class of structural elements, of which a column is the most common specific example
• Compressibility, a measure of volume change resulting from pressure
• Gas compression, raising the pressure and reducing the volume of gases
• Compression ratio, a figure of merit of an internal-combustion engine
• Compression (geology), a system of forces that tend to decrease the volume of rocks

In information science

• Data compression, the process of encoding digital information using fewer bits
• Audio compression (data), the compression of digital audio streams and files
• Bandwidth compression, a reduction in either the time to transmit or in the amount of bandwidth required to transmit
• Compression artifact, noticeable defects in audio or video that has been compressed
• Image compression, the application of data compression on digital images
• Video compression, the compression of digital video streams and files
• One-way compression function, a cryptographic primitive

In engineering

• Dynamic range compression, a compression process that reduces the dynamic range of an audio signal
• Gain compression, in electronic amplifiers, a reduction in differential or slope gain resulting from device non-linearity

In medicine

• Brain compression, a potentially fatal condition where pressure is exerted on the brain by internal bleeding
• Compression bandage, a bandage that uses compression to reduce the flow of blood
• Compression in pyelography involves pressing on the lower abdominal area, resulting in distension of the upper urinary tract.

In mathematics

• Compression (functional analysis), the compression of a linear operator "T" on a Hilbert space to a subspace "K" is the operator

Other

• Compression (phonetics), running syllables together in informal speech
• Compression (zoology) when an animal, or part of an animal, is shorter or narrower compared with other animals in the same group; e.g. the body of a lizard may be "compressed" (flattened) so it can better fit into crevices under rocks

See also

• Compaction (disambiguation)
• compress
• Compression shorts
• Compressor (disambiguation)
• Decompression (disambiguation)
• Expansion (disambiguation)

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

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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