Effects of light map orientation and shape on the visual perception of canonical materials

Abstract

We previously presented a systematic optics-based canonical approach to test material-lighting interactions in their full natural ecology, combining canonical material and lighting modes. Analyzing the power of the spherical harmonics components of the lighting allowed us to predict the lighting effects on material perception for generic natural illumination environments. To further understand how material properties can be brought out or communicated visually, in the current study, we tested whether and how light map orientation and shape affect these interactions in a rating experiment: For combinations of four materials, three shapes, and three light maps, we rotated the light maps in 15 different configurations. For the velvety objects, there were main and interaction effects of lighting and light map orientation. The velvety ratings decreased when the main light source was coming from the back of the objects. For the specular objects, there were main and interaction effects of lighting and shape. The specular ratings increased when the environment in the specular reflections was clearly visible in the stimuli. For the glittery objects, there were main and interaction effects of shape and light map orientation. The glittery ratings correlated with the coverage of the glitter reflections as the shape and light map orientation varied. For the matte objects, results were robust across all conditions. Last, we propose combining the canonical modes approach with so-called importance maps to analyze the appearance features of the proximal stimulus, the image, in contradistinction to the physical parameters as an approach for optimization of material communication.

Perceived roughness of glossy objects: The influence of Fresnel effects and correlated image statistics

“…A correct estimation of roughness seems to be especially difficult for homogeneous illuminations, even if they are real-world illuminations. More important than the realism of the mirrored scene seems to be the statistical nature of the illumination map, in particular the number and distribution of light sources (Dror, Willsky, & Adelson, 2004;Pont & te Pas, 2006;Zhang et al, 2019, Zhang, de Ridder, Barla, & Pont, 2020. Zhang et al (2019) distinguish in the direction of decreasing homogeneity the three canonical illumination categories ambient, focus, and brilliance, and found in their Experiment 2 that the gloss rating of a highly glossy material decreased with increasing illumination homogeneity.…”

“…A correct estimation of roughness seems to be especially difficult for homogeneous illuminations, even if they are real-world illuminations. More important than the realism of the mirrored scene seems to be the statistical nature of the illumination map, in particular the number and distribution of light sources ( Dror, Willsky, & Adelson, 2004 ; Pont & te Pas, 2006 ; Zhang et al., 2019 , Zhang, de Ridder, Barla, & Pont, 2020 ).…”

“…A possible interpretation of this result is that the two metrics, which are based on the illumination map alone, ignore some aspects of the illumination that are essential for gloss perception and gloss constancy. For example, a plausible additional factor that is ignored in these metrics is that the relevant portions of the illumination map depend on the orientation of the illumination, the object, and the observer relative to each other ( Zhang et al., 2020 ).…”

Scaling and discriminability of perceived gloss

“…This early observation suggested that a perceptually uniform color space would be a complex mathematical entity, and these complexities were not fully GLOSS SCALING AND DISCRIMINABILITY appreciated until the next century, when it was discovered that small differences in chromaticity could only be adequately specified within local regions of the CIE 1931 color space (MacAdam, 1943;Smith & Guild, 1931). Similarly, the prospect of a uniform perceptual space for surface gloss remains elusive because changes in illumination, shape, and viewpoint can drastically alter the perception of surface material properties (Fleming et al, 2003;Ho, Maloney, & Landy, 2007;Norman, Todd, & Phillips, 2020;Vangorp, Laurijssen, & Dutré, 2007;Zhang, de Ridder, Barla, & Pont, 2020), which therefore means that the validity of any gloss space will be constrained by the viewing conditions chosen for its construction (Fores, Fairchild, & Tastl, 2014). Despite these difficulties, our finding that MLDS provides a solution for both scaling and discriminability of gloss indicates that the construction of a perceptually uniform gloss space is a tractable problem.…”

Scaling and discriminability of perceived gloss

“…This early observation suggested that a perceptually uniform color space would be a complex mathematical entity, and these complexities were not fully GLOSS SCALING AND DISCRIMINABILITY appreciated until the next century, when it was discovered that small differences in chromaticity could only be adequately specified within local regions of the CIE 1931 color space (MacAdam, 1943;Smith & Guild, 1931). Similarly, the prospect of a uniform perceptual space for surface gloss remains elusive because changes in illumination, shape, and viewpoint can drastically alter the perception of surface material properties (Fleming et al, 2003;Ho, Maloney, & Landy, 2007;Norman, Todd, & Phillips, 2020;Vangorp, Laurijssen, & Dutré, 2007;Zhang, de Ridder, Barla, & Pont, 2020), which therefore means that the validity of any gloss space will be constrained by the viewing conditions chosen for its construction (Fores, Fairchild, & Tastl, 2014). Despite these difficulties, our finding that MLDS provides a solution for both scaling and discriminability of gloss indicates that the construction of a perceptually uniform gloss space is a tractable problem.…”