Institut für Psychologie, Universität Kiel, Kiel, Germany.
J Vis. 2021 Aug 2;21(8):1. doi: 10.1167/jov.21.8.1.
The roughness of a shiny surface determines how sharp the reflected image of the surroundings is, and thus whether the surface appears highly glossy or more or less matte. In a matching experiment, subjects were asked to reproduce the perceived roughness of a given surface (standard) in a comparison stimulus (match), where the standard and the match could differ in both shape and illumination. To compare the effect of the reflection model on the accuracy of the settings, this was done for two different reflectance models (bidirectional reflectance distribution function [BRDF]). The matching errors were smaller, that is, the constancy under shape and illumination changes higher, when Fresnel effects were physically correctly reproduced in the reflectance model (Fresnel-BRDF) than when this was not the case (Ward-BRDF). The subjects' settings in the experiment can be predicted very well by two image statistics, one of which is based on the mean edge strength and the other on a local discrete cosine transform. In particular, these predictions also reflect the empirically observed advantage of the Fresnel-BRDF. These results show that the constancy of perceived roughness across context changes may depend on the BRDF used, with Fresnel effects playing a significant role. The good prediction of subjects' settings using the two image statistics suggests that local brightness variance, which affects both image statistics, can be used as a valid cue for surface roughness.
光泽表面的粗糙度决定了周围环境反射图像的清晰度，因此表面看起来是高度有光泽还是或多或少有哑光。在匹配实验中，要求被试者在比较刺激（匹配）中再现给定表面（标准）的感知粗糙度，其中标准和匹配在形状和照明方面可以有所不同。为了比较反射模型对设置准确性的影响，对于两种不同的反射率模型（双向反射分布函数 [BRDF]）进行了此操作。当在反射率模型中物理上正确再现菲涅耳效应（菲涅耳-BRDF）时，匹配误差更小，即形状和照明变化下的恒定性更高，而当情况并非如此时（沃德-BRDF）则误差更大。实验中被试者的设置可以通过两种图像统计数据很好地预测，其中一种基于平均边缘强度，另一种基于局部离散余弦变换。特别是，这些预测还反映了菲涅耳-BRDF 的经验观察到的优势。这些结果表明，感知粗糙度在上下文变化中的恒定性可能取决于所使用的 BRDF，菲涅耳效应起着重要作用。使用两种图像统计数据对被试者设置的良好预测表明，影响这两种图像统计数据的局部亮度变化可以用作表面粗糙度的有效线索。
