Rate–Distortion Theory
An information-theoretic framework describing the fundamental trade-off between bitrate and acceptable reconstruction distortion in lossy compression.
Lossy coding generally exchanges fewer bits for more reconstruction error, but the best achievable trade-off depends on the source distribution and the chosen distortion measure. Rate–distortion theory describes that boundary independently of the details of a particular codec.
Although it shares the language of information theory with Information Entropy and channel capacity, it answers a different question: the cost of representing a source under controlled loss rather than reliable transmission over a noisy channel.