Image fidelity is the subset of overall image quality that specifically addresses the visual equivalence of two images. This paper describes an algorithm for determining whether the goal of image fidelity is met as a function of display parameters and viewing conditions. Using a digital image processing approach, this algorithm is intended for the design and analysis of image processing algorithms, imaging systems, and imaging media. The visual model, which is the central component of the algorithm, is comprised of three parts: an amplitude nonlinearity, a contrast sensitivity function, and a hierarchy of detection mechanisms.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.