147:, as illustrated in Figure 1. If one were to imagine that the figure represents snow, and that the polygons are its (transparent) ice crystallites, an impinging ray is partially reflected (a few percent) by the first particle, enters in it, is again reflected by the interface with the second particle, enters in it, impinges on the third, and so on, generating a series of "primary" scattered rays in random directions, which, in turn, through the same mechanism, generate a large number of "secondary" scattered rays, which generate "tertiary" rays, and so forth. All these rays walk through the snow crystallites, which do not absorb light, until they arrive at the surface and exit in random directions. The result is that the light that was sent out is returned in all directions, so that snow is white despite being made of transparent material (ice crystals).
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158:: one can describe them as made of a 3D mosaic of small, irregularly shaped defective crystals. Organic materials are usually composed of fibers or cells, with their membranes and their complex internal structure. And each interface, inhomogeneity or imperfection can deviate, reflect or scatter light, reproducing the above mechanism.
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Most materials can give some specular reflection, provided that their surface can be polished to eliminate irregularities comparable with the light wavelength (a fraction of a micrometer). Depending on the material and surface roughness, reflection may be mostly specular, mostly diffuse, or anywhere
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And, when a colored object has both diffuse and specular reflection, usually only the diffuse component is colored. A cherry reflects diffusely red light, absorbs all other colors and has a specular reflection which is essentially white (if the incident light is white light). This is quite general,
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For simplicity, "reflections" are spoken of here, but more generally the interface between the small particles that constitute many materials is irregular on a scale comparable with light wavelength, so diffuse light is generated at each interface, rather than a single reflected ray, but the story
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Diffusion affects the color of objects in a substantial manner because it determines the average path of light in the material, and hence to which extent the various wavelengths are absorbed. Red ink looks black when it stays in its bottle. Its vivid color is only perceived when it is placed on a
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specular reflection. Among common materials, only polished metals can reflect light specularly with high efficiency, as in aluminum or silver usually used in mirrors. All other common materials, even when perfectly polished, usually give not more than a few percent specular reflection, except in
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Diffuse reflection from solids is generally not due to surface roughness. A flat surface is indeed required to give specular reflection, but it does not prevent diffuse reflection. A piece of highly polished white marble remains white; no amount of polishing will turn it into a mirror. Polishing
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scattering material (e.g. paper). This is so because light's path through the paper fibers (and through the ink) is only a fraction of millimeter long. However, light from the bottle has crossed several centimeters of ink and has been heavily absorbed, even in its red wavelengths.
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Up to this point white objects have been discussed, which do not absorb light. But the above scheme continues to be valid in the case that the material is absorbent. In this case, diffused rays will lose some wavelengths during their walk in the material, and will emerge colored.
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The vast majority of visible objects are seen primarily by diffuse reflection from their surface. Exceptions include objects with polished (specularly reflecting) surfaces, and objects that themselves emit light.
287:. In real life terms what this means is that light is reflected off non-shiny surfaces such as the ground, walls, or fabric, to reach areas not directly in view of a light source. If the diffuse surface is
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The visibility of objects, excluding light-emitting ones, is primarily caused by diffuse reflection of light: it is diffusely-scattered light that forms the image of the object in the observer's eye.
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reflected from an object strikes other objects in the surrounding area, illuminating them. Diffuse interreflection specifically describes light reflected from objects which are not shiny or
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Few materials do not cause diffuse reflection: among these are metals, which do not allow light to enter; gases, liquids, glass, and transparent plastics (which have a liquid-like
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in between. A few materials, like liquids and glasses, lack the internal subdivisions which produce the subsurface scattering mechanism described above, and so give
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of a glass prism, or when structured in certain complex configurations such as the silvery skin of many fish species or the reflective surface of a
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can be used to determine the absorption spectra of powdered samples in cases where transmission spectroscopy is not feasible. This applies to
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This mechanism is very general, because almost all common materials are made of "small things" held together. Mineral materials are generally
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540:
Fuller, Michael P.; Griffiths, Peter R. (1978). "Diffuse reflectance measurements by infrared
Fourier transform spectrometry".
222:. Diffuse reflection can be highly efficient, as in white materials, due to the summing up of the many subsurface reflections.
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of an eye. These materials can reflect diffusely, however, if their surface is microscopically rough, like in a
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Or, if the object is thin, it can exit from the opposite surface, giving diffuse transmitted light.
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A surface may also exhibit both specular and diffuse reflection, as is the case, for example, of
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produces some specular reflection, but the remaining light continues to be diffusely reflected.
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The most general mechanism by which a surface gives diffuse reflection does not involve
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302:. There are a number of ways to model diffuse interreflection when rendering a scene.
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as used in home painting, which give also a fraction of specular reflection, while
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Figure 1 – General mechanism of diffuse reflection by a solid surface (
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because, except for metals, the reflectivity of most materials depends on their
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SIGGRAPH ’93 Proceedings, J. T. Kajiya, Ed., vol. 27, pp. 165–174
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Diffuse and specular reflection from a glossy surface. The rays represent
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Figure 2 – Diffuse reflection from an irregular surface
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Only primary and secondary rays are represented in the figure.
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Reflection from layered surfaces due to subsurface scattering
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Photoelectric sensors and controls: selection and application
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Reflectance spectroscopy
Principles, methods, applications
298:, diffuse interreflection is an important component of
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for the white color of the water droplets in clouds.
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A surface built from a non-absorbing powder such as
521:(1926). "Light Scattering by Inhomogeneous Media".
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Proceedings of ACM SIGGRAPH 2001', pp. 511–518
199:paints give almost exclusively diffuse reflection.
264:is responsible for the blue color of the sky, and
143:the surface: most of the light is contributed by
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434:A practical model for subsurface light transport
69:rather than at just one angle as in the case of
23:Reflection with light scattered at random angles
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77:diffuse reflecting surface is said to exhibit
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85:when viewed from all directions lying in the
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96:, or from fibers such as paper, or from a
16:For reflection of charged particles, see
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475:Ein Beitrag zur Optik der Farbanstriche
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484:The Kubelka-Munk Theory of Reflectance
145:scattering centers beneath the surface
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473:Paul Kubelka, Franz Munk (1931),
408:P.Hanrahan and W.Krueger (1993),
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398:from the original on 2018-01-14.
319:Diffuse reflectance spectroscopy
38:for an ideal diffuse reflector.
344:List of reflected light sources
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310:are two commonly used methods.
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81:, meaning that there is equal
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212:reflection by a lake, or the
349:Oren–Nayar reflectance model
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34:, which varies according to
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477:, Zeits. f. Techn. Physik,
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61:incident on the surface is
57:from a surface such that a
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432:H.W.Jensen et al. (2001),
208:particular cases, such as
151:can be told the same way.
123:phenomena not represented)
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384:. CRC Press. p. 29.
327:mid-infrared spectroscopy
89:adjacent to the surface.
165:microscopic structure);
575:KortĂĽm, Gustav (1969).
523:Zh. Russ. Fiz-Khim. Ova
505:The Scattering of Light
277:Diffuse interreflection
100:material such as white
378:Scott M. Juds (1988).
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507:. New York: Academic.
279:is a process whereby
255:Importance for vision
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79:Lambertian reflection
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579:. Berlin: Springer.
542:Analytical Chemistry
296:3D computer graphics
245:chromatic dispersion
36:Lambert's cosine law
554:10.1021/ac50035a045
503:Kerker, M. (1969).
300:global illumination
262:Rayleigh scattering
71:specular reflection
490:2011-07-17 at the
443:2010-07-27 at the
419:2010-07-27 at the
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55:waves or particles
43:Diffuse reflection
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32:luminous intensity
615:Optical phenomena
548:(13): 1906–1910.
391:978-0-8247-7886-6
220:dielectric mirror
185:of the eye lens.
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179:frost glass
609:Categories
365:References
323:UV-Vis-NIR
121:refraction
87:half-space
47:reflection
595:714802320
562:0003-2700
359:Remission
304:Radiosity
183:cataracts
163:amorphous
111:Mechanism
83:luminance
63:scattered
53:or other
488:Archived
441:Archived
417:Archived
396:Archived
339:Diffuser
333:See also
285:specular
173:and the
65:at many
620:Shading
289:colored
141:exactly
94:plaster
73:. An
45:is the
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193:paints
190:glossy
171:cornea
102:marble
67:angles
412:, in
281:light
249:prism
247:in a
197:matte
75:ideal
51:light
591:OCLC
581:ISBN
558:ISSN
386:ISBN
306:and
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175:lens
550:doi
294:In
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49:of
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