Lossy Compression of Individual Sequences Revisited: Fundamental Limits of Finite-State Encoders

Abstract

We extend Ziv and Lempel's model of finite-state encoders to the realm of lossy compression of individual sequences. In particular, the model of the encoder includes a finite-state reconstruction codebook followed by an information lossless finite-state encoder that compresses the
 reconstruction codeword with no additional distortion. We first derive two different lower bounds to the compression ratio that depend on the number of states of the lossless encoder. Both bounds are asymptotically achievable by conceptually simple coding schemes. We then show that when the number of states of the lossless encoder is large enough in terms of the reconstruction
 block-length, the performance can be improved, sometimes significantly so.
 In particular, the improved performance is achievable using a random-coding ensemble
 that is universal, not only in terms of the source sequence, but also in terms
 of the distortion measure.