# Variable-Length Lossy Compression Allowing Positive Overflow and Excess Distortion Probabilities

## TL;DR

This paper develops new bounds and explicit code constructions for variable-length lossy source coding that allows positive probabilities of exceeding distortion and codeword length limits, using smooth max entropy.

## Contribution

It introduces novel one-shot achievability and converse bounds based on smooth max entropy and provides explicit code constructions for variable-length lossy compression with overflow and excess distortion probabilities.

## Key findings

- Derived one-shot bounds for optimal rate
- Provided explicit code construction based on distortion balls
- Achieved single-letter asymptotic rate characterization

## Abstract

This paper investigates the problem of variable-length lossy source coding allowing a positive excess distortion probability and an overflow probability of codeword lengths. Novel one-shot achievability and converse bounds of the optimal rate are established by a new quantity based on the smooth max entropy (the smooth R\'enyi entropy of order zero). To derive the achievability bounds, we give an explicit code construction based on a distortion ball instead of using the random coding argument. The basic idea of the code construction is similar to the optimal code construction in the variable-length lossless source coding. Our achievability bounds are slightly different, depending on whether the encoder is stochastic or deterministic. One-shot results yield a general formula of the optimal rate for blocklength $n$. In addition, our general formula is applied to asymptotic analysis for a stationary memoryless source. As a result, we derive a single-letter characterization of the optimal rate by using the rate-distortion and rate-dispersion functions.