Rate-Distortion-Perception Tradeoff for Gaussian Vector Sources

TL;DR

This paper explores the rate-distortion-perception tradeoff for Gaussian vector sources, deriving explicit solutions and revealing how perception constraints alter traditional rate allocation strategies.

Contribution

It provides a novel explicit characterization of the RDP tradeoff for Gaussian sources under perception constraints, extending classical rate-distortion theory.

Findings

Jointly Gaussian reconstructions are optimal for Gaussian sources.

Perception constraints ensure all source components receive positive rates.

Optimal rate allocation involves unequal water levels under perception constraints.

Abstract

This paper studies the rate-distortion-perception (RDP) tradeoff for a Gaussian vector source coding problem where the goal is to compress the multi-component source subject to distortion and perception constraints. Specifically, the RDP setting with either the Kullback-Leibler (KL) divergence or Wasserstein-2 metric as the perception loss function is examined, and it is shown that for Gaussian vector sources, jointly Gaussian reconstructions are optimal. We further demonstrate that the optimal tradeoff can be expressed as an optimization problem, which can be explicitly solved. An interesting property of the optimal solution is as follows. Without the perception constraint, the traditional reverse water-filling solution for characterizing the rate-distortion (RD) tradeoff of a Gaussian vector source states that the optimal rate allocated to each component depends on a constant, called the water level. If the variance of a specific component is below the water level, it is assigned a zero compression rate. However, with active distortion and perception constraints, we show that the optimal rates allocated to the different components are always positive. Moreover, the water levels that determine the optimal rate allocation for different components are unequal. We further treat the special case of perceptually perfect reconstruction and study its RDP function in the high-distortion and low-distortion regimes to obtain insight to the structure of the optimal solution.