Understanding Compression

Glossary of Compression Words

7zip

A file archiver with a high compression ratio.

Alpha blending

The process of combining an image with a background to create the appearance of partial or full transparency.

Alpha channel

An additional channel (in addition to RGB) that contains a value between 0 and 1 that designates the transparency for each pixel.

Alpha transparency

The transparency value for a pixel as transmitted in the Alpha channel.

Arithmetic coding

An algorithm for encoding data, wherein frequently used characters are stored with fewer bits and not-so-frequently occurring characters are stored with more bits, resulting in fewer bits used in total. Rather than assigning codewords to symbols in a 1:1 fashion, this algorithm transforms the entire input stream from a set of symbols to one (excessively long) numeric value, whose LOG2 representation is closer to the true value of entropy for the stream.

See Chapter 5.

Asymmetric numeral systems (ANS)

A modern variant of statistical compression, which has shown early promise in achieving close to entropy compression with performance comparable to Huffman coding.

See Chapter 5.

Binary or base 2 number system

A way of representing numbers using only the digits 0 and 1, and each shift in position is by a power of 2. For example, the decimal number 5 would be 101 or 2⁰ + 2².

See Chapter 2.

Binary erasure channel

A communications channel model used for analysis in information theory. The idea is that ...