Abstract
We have previously introduced frequency-band based analyses as an approach to infer material properties like roughness, thickness, and volume from images of fabrics (Giesel & Zaidi, Frequency based perception of material properties, Current Biology, under review). Here, we address how these material properties and their frequency-band representations are influenced by viewing parameters such as the distance or angle, and the illumination direction. To determine whether the viewing distance has an influence on the perception of material properties, we varied it by using two CRTs. The reference monitor was placed at a distance of 66cm, while the comparison monitor was placed at 33, 66, or 132cm. The original stimulus was displayed on the comparison monitor, while either the original or one of four manipulated versions of the original image was shown on the reference monitor. The observers' task was to indicate which of the images of a fabric displayed on the two monitors appeared as having more volume, as being thicker, or rougher, respectively. The results showed that over the tested range of viewing distances the perception of material properties remained largely constant indicating that the visual inference of material properties is more likely to be based on estimated material spatial frequency than on retinal frequency. We complemented the psychophysical results by image analyses using images from the KTH-TIPS database containing images of materials photographed at different distances, slants, and illumination directions. We show that the changes in material appearance are closely reflected in the frequency-band signatures. Finally, we present results from an experiment in which observers ranked printed versions of fabric images according to their volume, thickness, and roughness. We show that observers' ratings were closely correlated with amplitudes in the three frequency bands we identified previously.
Meeting abstract presented at VSS 2013