A single-ended blockiness measure for JPEG-coded images

Abstract

In three subjective experiments, dissimilarity data and numerical category scaling data were obtained to determine the underlying attributes of image quality in sequential baseline-coded JPEG images. Although several distortions were perceived, namely blockiness, ringing and blur, the subjective data for all attributes were highly correlated, so that image quality could approximately be described in one dimension. We therefore proceeded by developing an instrumental measure for one of the distortions, namely, blockiness. In this paper a single-ended blockiness measure is proposed, i.e., one that uses only the coded image. Our approach is therefore fundamentally different from most (double-ended) image quality models that need both the original and the degraded image. The proposed measure is based on detecting the low-amplitude edges that result from blocking and estimating the edge amplitudes. Because of the approximate one-dimensionality of the underlying psychological space, the proposed blockiness measure also predicts the image quality of sequential baseline coded JPEG images.