Pont Sylvia C, van Doorn Andrea J, Koenderink Jan J
Perceptual Intelligence (π-)lab, Department of Industrial Design Engineering, Delft University of Technology, The Netherlands.
Laboratory of Experimental Psychology, University of Leuven, Belgium; Laboratory of Experimental Psychology, Faculty of Social Sciences, Utrecht University, The Netherlands.
Iperception. 2017 Apr 13;8(2):2041669517701947. doi: 10.1177/2041669517701947. eCollection 2017 Mar-Apr.
We studied whether human observers can estimate the illumination direction from of random Brownian surfaces, containing undulations over a range of scales. The locally Lambertian surfaces were illuminated with a collimated beam from random directions. The surfaces had a uniform albedo and thus texture appeared only through shading and shadowing. The data confirm earlier results with Gaussian surfaces, containing undulations of a single scale. Observers were able to accurately estimate the source azimuth. If shading dominated the images, the observers committed 180° errors. If cast shadows were present, they resolved this convex-concave-ambiguity almost completely. Thus, observers relied on second-order statistics in the shading regime and used an unidentified first-order cue in the shadow regime. The source elevations could also be estimated, which can be explained by the observers' exploitation of the statistical homogeneity of the stimulus set. The fraction of the surface that is in shadow and the median intensity are likely cues for these elevation estimates.
我们研究了人类观察者是否能够从包含一系列尺度起伏的随机布朗表面估计光照方向。局部朗伯表面由来自随机方向的准直光束照明。这些表面具有均匀的反照率，因此纹理仅通过明暗和阴影显现。数据证实了早期关于包含单一尺度起伏的高斯表面的结果。观察者能够准确估计光源方位角。如果明暗主导图像，观察者会出现180°的误差。如果存在投射阴影，他们几乎完全解决了这种凸凹模糊性。因此，观察者在明暗区域依赖二阶统计量，并在阴影区域使用了一个未识别的一阶线索。光源仰角也可以被估计，这可以通过观察者对刺激集统计同质性的利用来解释。处于阴影中的表面比例和中值强度可能是这些仰角估计的线索。
