Abstract
MatMix 1.0 is a novel material probe we developed for quantitatively measuring visual perception of materials. We implemented optical mixing of four canonical scattering modes, represented by photographs, as the basis of the probe. In order to account for a wide range of materials, velvety and glittery (asperity and meso-facet scattering) were included besides the common matte and glossy modes (diffuse and forward scattering). To test the probe, we conducted matching experiments in which inexperienced observers were instructed to adjust the modes of the probe to match its material to that of a test stimulus. Observers were well able to handle the probe and match the perceived materials. Results were robust across individuals, across combinations of materials, and across lighting conditions. We conclude that the approach via canonical scattering modes and optical mixing works well, although the image basis of our probe still needs to be optimized. We argue that the approach is intuitive, since it combines key image characteristics in a "painterly" approach. We discuss these characteristics and how we will optimize their representations.
Highlights
Natural materials scatter light in various manners
Instead of directly combining reflectance functions, we propose to linearly superpose images of objects with the same shape but finished with different materials
We find that (a) MatMix 1.0 could be implemented by replacing the basis images of the stimuli and the probe with rendered images and (b) with renderings as the basis images, observers can still perform the task well
Summary
Natural materials scatter light in various manners. Even if we limit ourselves to the main scattering characteristics of opaque materials, we probably still need about a dozen scattering types or canonical modes to represent most materials. Bidirectional reflectance distribution functions (BRDFs) provide a physical description of how opaque material surfaces scatter light. If the scattering properties or optical characteristics of materials can be accurately described, the so-called forward rendering problem can be solved. We do not see BRDFs. On the one hand, a BRDF combined with various object shapes and lighting conditions can result in different images of the same material (we consider an image as the resulting optical structure projected on a picture or the retina). Different combinations of BRDF, object shape, and lighting can result in similar images. Images contain ambiguities of material, shape, and light
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