Browsing by Subject "Shading"

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Open Access
Ray tracing geometric models and parametric surfaces
(1989) İşler, Veysi
In many computer graphics applications such as CAD, realistic displays have very important and positive effects on designers using the system. There axe several techniques to generate realistic images with the computer. Ray tracing gives the most effective results by simulating the interaction of light with its environment. Furthermore, this technique can be easily adopted to many physical phenomena such as reflection, refraction, shadows, etc. by which the interaction of many different objects with each other could be realistically simulated. However, it may require excessive amount of time to generate an image. In this thesis , we studied the ray tracing algorithm arid the speed problem associated with it and several methods developed to overcome this problem. We also implemented a ray tracer system that could be used to model a three dimensional scene and And out the lighting effects on the objects.
Open Access
Relative flattening between velvet and matte 3D shapes: Evidence for similar shape-from-shading computations
(Association for Research in Vision and Ophthalmology, 2012) Wijntjes, M. W. A.; Doerschner, K.; Kucukoglu, G.; Pont, S. C.
Among other cues, the visual system uses shading to infer the 3D shape of objects. The shading pattern depends on the illumination and reflectance properties (BRDF). In this study, we compared 3D shape perception between identical shapes with different BRDFs. The stimuli were photographed 3D printed random smooth shapes that were either painted matte gray or had a gray velvet layer. We used the gauge figure task (J. J. Koenderink, A. J. van Doorn, & A. M. L. Kappers, 1992) to quantify 3D shape perception. We found that the shape of velvet objects was systematically perceived to be flatter than the matte objects. Furthermore, observers' judgments were more similar for matte shapes than for velvet shapes. Lastly, we compared subjective with veridical reliefs and found large systematic differences: Both matte and velvet shapes were perceived more flat than the actual shape. The isophote pattern of a flattened Lambertian shape resembles the isophote pattern of an unflattened velvet shape. We argue that the visual system uses a similar shape-from-shading computation for matte and velvet objects that partly discounts material properties.