Effects of specular roughness on the perception of color and opacity.

Previous studies have shown that information concerning object shape is important for the perception of translucency. This study aims to explore how the perception of semi-opaque objects is influenced by surface gloss. We varied specular roughness, specular amplitude, and the simulated direction of a light source used to illuminate a globally convex bumpy object. We found that perceived lightness and roughness increased as specular roughness was increased. Declines in perceived saturation were observed but were far smaller in magnitude with these increases in specular roughness. There were inverse correlations found between perceived gloss and perceived lightness, perceived transmittance and perceived saturation, and between perceived roughness and perceived gloss. Positive correlations were found between perceived transmittance and glossiness, and between perceived roughness and perceived lightness. These findings suggest that specular reflections influence the perception of transmittance and color attributes, and not just perceived gloss. We also performed follow-up modeling of image data to find that perceived saturation and lightness could be explained by the reliance on different image regions with greater chroma and lower lightness, respectively. We also found systematic effects of lighting direction on perceived transmittance that indicate there are complex perceptual interactions that require further consideration.

Surface properties and the perception of color.

We examined whether perception of color saturation and lightness depends on the three-dimensional (3D) shape and surface gloss of surfaces rendered to have different hues. In Experiment 1, we parametrically varied specular roughness of predominantly planar surfaces with different mesoscopic relief heights. The orientation of surfaces was varied relative to the light source and observer. Observers matched perceived lightness and chroma (effectively saturation) using spherical objects rendered using CIE LCH color space. We observed strong interactions between perceived saturation and lightness with changes in surface orientation and surface properties (specular roughness and 3D relief height). Declines in saturation and increases in lightness were observed with increasing specular roughness. Changes in relief height had greater effects on perceived saturation and lightness for blue hues compared with reddish and greenish hues. Experiment 2 found inverse correlations between perceived gloss and specular roughness across conditions. Experiment 3 estimated perceived specular coverage and found that a weighted combination of perceived gloss and specular coverage could account for perceived color saturation and lightness, with different coefficients accounting for the perceptual experience for each of the three hue conditions. These findings suggest that perceived color saturation and lightness depend on the separation of specular highlights from diffuse shading informative of chromatic surface reflectance.

Effects of Shape, Roughness and Gloss on the Perceived Reflectance of Colored Surfaces.

This study examined perceptual differentiation of specular from diffuse shading for the recovery of surface color and gloss. In Experiment 1, we parametrically varied the mesoscale relief height of globally planar surfaces, specular sharpness and the orientation of the surface relative to the light source. We obtained psychophysical matches for perceived color saturation and value (HSV), but also considered whether the main effects could be influenced by color space used when transforming data to perceptually-uniform CIE LCH space. Results revealed strong interactions between perceived color attributes and the lighting conditions, the structure of specular reflections, and surface relief. Declines in saturation were observed with increasing specular roughness (using an HSV color representation), but no similar decline was observed in chroma (using a CIE LCH color representation). Experiment 2 found strong negative correlations between perceived gloss and specular roughness. Perceived gloss also depended on mesoscopic relief height and orientation of the surface relative to the light source. Declines in perceived gloss moderately accounted for the variability in color saturation and value matches obtained in Experiment 1. We found information about perceived specular coverage could further improve the model's accountability of perceived color saturation and lightness (Experiment 3). These findings together suggest that perceived color saturation and color value depends on the visual system's ability to distinguish the underlying diffuse shading from specular highlights in images.

Imaging and applied optics: introduction to the feature issue.

This special issue of Applied Optics contains selected papers from OSA's Imaging Congress with particular emphasis on work from mathematics in imaging, computational optical sensing and imaging, imaging systems and applications, and 3D image acquisition and display.

Measurement of the lens optical transfer function using a tartan pattern.

We present a method for measuring the optical transfer function (OTF) of a camera lens using a tartan test pattern containing sinusoidal functions with multiple frequencies and orientations. The method is designed to optimize measurement accuracy for an adjustable set of sparse spatial frequencies and be reliable and fast in a wide range of measurement conditions. We describe the pattern design and the algorithm for estimating the OTF accurately from a captured image. Simulations show the tartan method is significantly more accurate than the International Organization for Standardization 12233 standard slanted-edge method. Experimental results from the tartan method were reproducible to 0.01 root mean square and in reasonable agreement with the slanted-edge method.