Fixed-length lossy code ($R_n=n^{-1}{\log }_2{M}_n$)

A fixed-length lossy code maps a block of $n$ source symbols to one of $M_n$ messages, then maps that message to a reconstruction block. The encoder and decoder together define the reconstruction. Its rate is ${\log }_2{M}_n/n$ bits per source symbol; an implementation using a fixed binary message needs $\lceil {\log }_2{M}_n\rceil$ transmitted bits per block. Its performance also depends on expected distortion, block length, and the chosen distortion measure.