Comparing realness between real objects and images at various resolutions

Abstract

Image resolution is one of the important factors for visual realness. We performed subjective assessments to examine the realness of images at six different resolutions, ranging from 19.5 cpd (cycles per degree) to 156 cpd. A paired-comparison procedure was used to quantify the realness of six images versus each other or versus the real object. Three objects were used. Both real objects and images were viewed through a synopter, which removed horizontal disparity and presented the same image to both eyes. Sixty-five observers were asked to choose the viewed image which was closer to the real object and appeared to be there naturally for each pair of stimuli selected from the group of six images and the real object. It was undisclosed to the observers that real objects were included in the stimuli. The paired comparison data were analyzed using the Bradley-Terry model. The results indicated that realness of an image increased as the image resolution increased up to about 40-50 cpd, which corresponded to the discrimination threshold calculated based on the observers' visual acuity, and reached a plateau above this threshold.