4/19/2023 0 Comments Specular reflectionThe specular Phong term K scos(θ) spec is augmented by modifying the K s and spec parameters to a more complex and physically accurate form. The Gaussian BRDF is a better model, and with some simplifications can be approximated by modifying parameters in the Phong model. It's difficult to map measured physical lighting properties to its coefficient, and at low specularity it doesn't conserve incident and reflected energy. The Phong lighting equation, with its cosine raised to a power term for the specular component, is a poor fit to a physically accurate specular reflectance model. TOM McREYNOLDS, DAVID BLYTHE, in Advanced Graphics Programming Using OpenGL, 2005 15.9.2 Gaussian Reflection Many intermediate geometries are possible, which give rise to sensations of sheen and gloss these usually enable one to predict the felt hardness or smoothness of surface without actually touching them. Because of the absorptive properties of the pigments, some wavelengths reflect more copiously than others, providing the physical basis for the perceived color of the object. Light not absorbed is scattered within this layer with an intensity pattern that may approximate that of a perfectly diffuse reflector. The remainder is refracted into the layers below, which contain diffusely reflecting, spectrally selective absorptive pigments suspended in a binding matrix. The hard, highly polished outer surface exhibits specular reflectance of some of the incident light. Some simultaneously exhibit specular and diffuse reflectance that of a new automobile provides a familiar example. No real surface behaves in exactly this way, although some surfaces approach it. Intensity distribution of light reflected from a perfectly diffuse (Lambertian) surface, showing proportion of reflected light within 5° of each indicated direction. More often, because highlights from most surfaces do not alter the spectral distribution of incident light, specular reflection provides information about the color of the source of light rather than that of the surface.įIGURE 9. They also reflect diffusely from within but do so selectively with wavelength so that the specular reflection is seen to be tinged with the color of the diffuse component. In particular, highly polished surfaces of metals such as gold, steel, silver, and copper reflect specularly. If free of dust and suitably framed, the surface of an even less than ideal real mirror is not perceived at all instead, the virtual image of an object located physically in front of the mirror is seen as if positioned behind.Īlthough specular reflectance seldom provides information about the color of a surface, there are exceptions. An ideal mirror reflects all incident light nonselectively with wavelength. Boynton, in Encyclopedia of Physical Science and Technology (Third Edition), 2003 IV.A Specular and Diffuse ReflectanceĪ familiar example of specular reflectance is provided by a plane mirror, in which the angles of light incidence and reflectance are equal. Therefore, the continuity conditions cannot be satisfied unless there is another wave propagating backward from the surface into the first medium, in addition to the wave propagating forward from the surface into the second medium.Robert M. If the fields constitute an electromagnetic wave propagating through the surface from one medium to another, the amplitudes of the fields are different within the two regions. Whenever a volume contains a boundary separating regions of differing electric or magnetic constants, the components of D e and B m perpendicular to the surface and the components of E e and H m tangential to the surface must be continuous across the boundary. Third, it is one of the mechanisms by which light is scattered from a particle whose size is large compared with the wavelength, so that an understanding of this phenomenon is necessary to an understanding of diffuse reflectance from planetary regoliths.īoundary conditions in electromagnetic theory Second, it occurs in remote-sensing applications when light is reflected from smooth parts of a planetary surface, such as the ocean. First, it is an important tool for investigating properties of materials in the laboratory. Specular reflection is important to the topic of this book for several reasons. In this chapter the specular or mirror-like reflection that occurs when a plane electromagnetic wave encounters a plane surface separating two regions with different refractive indices is discussed quantitatively, along with the accompanying transmission, or refraction, through the interface.
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