2-1/2D texture mapping: real-time perceptual surface roughening

We applied fundamental perceptual and physico-mathematical studies to a fast method for luminance remapping of 2D texture maps which enhances perceived surface roughness in comparison with conventional 2D texture mapping. The fundamental physical mechanism underlying the method is the fact that texture contrast increases as the incident illumination tends towards grazing for rough matte surfaces, actually "exploding" near the shadow edge [Pont and Koenderink 2005]. A psychophysical study by Ho et al. [Ho et al. 2006] confirmed that human observers use texture contrast as a cue for relief-depth or surface roughness. Thus, 2D texture-mapped objects will appear to have a rougher surface if the texture contrast is increased as a function of the local illumination angle. In particular, we increase the bidirectional texture contrast in close accordance with the contrast gradients measured for real objects with rough surfaces. The method presented works well for random textures of locally-matte surfaces if the original texture does not have a contrast that is too high. This modification is in addition to the usual attenuation of the surface irradiance due to the angle of the incident illumination and the computational costs of the technique are similar to that of conventional diffuse shading. This low cost makes it straightforward to implement the technique with real-time shaders which allow interactive rendering on modern graphics hardware.