Data compression

Data compression encodes information using fewer bits than a chosen original representation. Lossless methods preserve exact data; lossy methods discard information to reduce size.

Run-length encoding: A lossless method that replaces consecutive repeated symbols with a symbol and its repetition count. It compresses long runs by representing repeated values compactly.
Entropy (information theory): A measure of the average uncertainty or information content of a random variable. It sets a lower bound on average lossless code length under a known probability model.
JPEG: A family of image compression standards commonly using block transforms and quantization. It illustrates lossy compression tuned to photographic images and human vision.
Lossless compression: Compression that allows exact reconstruction of the original data after decompression. It is required when even small changes to the data are unacceptable.
Bandwidth (computing): The data-carrying capacity of a communication channel over a given interval. Compression can lower the number of bits that must cross a constrained channel.
Huffman coding: A lossless coding method that assigns shorter bit strings to more frequent symbols and longer strings to rarer ones. It reduces average code length when symbol frequencies are uneven.
Source coding theorem: A result specifying the minimum achievable average rate for losslessly encoding a source with known statistics. It explains why no lossless compressor can beat the source's entropy indefinitely.
PNG: A raster image format that uses lossless compression and supports transparency. It preserves exact pixel values where JPEG's lossy encoding does not.
Lossy compression: Compression that irreversibly discards information to achieve smaller representations. It trades exact recovery for greater size reduction or acceptable perceptual quality.
Storage virtualization: The recording and retention of digital information on physical or networked media. Compression increases how much information can fit within a fixed storage capacity.

Linked from 24 pages