A psychophysical experiment was performed to determine the psychological dimensions involved in judging image quality. Seven different prints for each of two images, a portrait and a landscape, were produced using a combination of 5 printers and different paper types. The experiment consisted of two parts that were run concurrently. In the first part, paired-comparison was used to evaluate image preference. In the second part, judgments of similarity and dissimilarity were made using triad presentations. The paired-comparison data were analyzed using Thurstone's Law of Comparative Judgment and Dual Scaling, a multidimensional statistical technique that reveals the independent dimensions used in categorical judgments. The judgments of similarity and dissimilarity were analyzed using nonmetric multidimensional scaling. The results indicate that the psychological stimulus space can be characterized well in two dimensions. An ideal point model can be used to identify preference in this space. Variation in subjects' preferences can be characterized predominantly in one dimension and the subjects are fairly consistent in their response along this dimension. The psychological stimulus space correlated highly with color variation in the images. We conclude that multidimensional techniques can be used to analyze image preference and find relationships between psychological and physical variables relating to image quality. Specifically, our results indicate that color is of primary importance for judging image quality in our particular situation.