Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Rate distortion theory is a major branch of information theory which provides the theoretical foundations for lossy data compression; it addresses the problem of determining the minimal amount of entropy (or information) R that should be communicated over a channel, so that the source (input signal) can be approximately reconstructed at the receiver (output signal) without exceeding a given distortion D.Rate distortion theory gives theoretical bounds for how much compression can be achieved using lossy compression methods. Many of the existing audio, speech, image, and video compression techniques have transforms, quantization, and bit-rate allocation procedures that capitalize on the general shape of rate distortion functions.Rate distortion theory was created by Claude Shannon in his foundational work on information theory.