Evaluation of CRT-Displayed Digital Imagery Using Subjective Scaling

Abstract

Rapid technological transition from analog images to digital images has necessitated the development of a research program for evaluating digital image quality. This paper investigated the perceived interpretability of static, digitized monochrome images displayed on CRTs. Quality judgments of two image degradations: blur and noise, were evaluated by a subjective scaling technique. The digital images consisted of 10 scenes, each of which was degraded by 5 levels of blur and 5 levels of noise, yielding a set of 250 images. Fifteen Air Force photointerpreters participated in the study. The photointerpreters viewed the images on CRTs and rated the interpretability of each image on a 10-point NATO scale. Analysis of the scaling values indicated that the blur, noise, and interaction effects were statistically significant. Perceived interpretability of the images decreased monotonically as the physical image degradation increased. In a separate study, the photointerpreters extracted information from a selected subset of images. Correlation between the scaling values and the actual information extracted was high. This result suggests that information extraction performance can be accurately predicted from subjective quality judgments. Comparisons between CRT-displayed imagery with film-based digital imagery showed no differences. Subjective quality judgments were similar for the two display formats.