Discrete cosine transform - Wikipedia
signal-processingdata-compressionimage-compressionfourier-analysis
Abstraction: Cosine-based transform for signal compression used in JPEG, MPEG, MP3
Key points:
- DCT expresses a finite sequence as a sum of cosine functions at different frequencies; first proposed by Nasir Ahmed in 1972, published 1974 with K.R. Rao
- DCT-II is "the DCT" and its inverse (DCT-III) is "the IDCT"; eight standard variants exist, four common
- Strong energy compaction property: most signal energy concentrates in few coefficients; achieves 8:1 to 100:1 compression ratios
- Used in JPEG (1992), MPEG, H.26x video standards, MP3/AAC audio, HDTV, and virtually all digital media compression
- Integer DCT approximation used in AVC (2003) and HEVC (2013) with variable block sizes 4x4 to 32x32 pixels
- Related to DFT but uses only real numbers and even symmetry; equivalent to DFT of roughly twice the length
Connections: Nasir Ahmed · Jpeg · Discrete Cosine Transform · Data Compression · Signal Processing
Source: http://en.wikipedia.org/wiki/Discrete_cosine_transform