Specularity is the visual appearance of
specular reflection
Specular reflection, or regular reflection, is the mirror-like reflection of waves, such as light, from a surface.
The law of reflection states that a reflected ray of light emerges from the reflecting surface at the same angle to the su ...
s.
In computer graphics
In
computer graphics
Computer graphics deals with generating images with the aid of computers. Today, computer graphics is a core technology in digital photography, film, video games, cell phone and computer displays, and many specialized applications. A great deal ...
, it means the quantity used in three-dimensional (3D)
rendering which represents the amount of
reflectivity
The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electroni ...
a surface has. It is a key component in determining the
brightness
Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. The perception is not linear to luminance, ...
of
specular highlights, along with
shininess to determine the size of the
highlights.
It is frequently used in
real-time computer graphics
Real-time computer graphics or real-time rendering is the sub-field of computer graphics focused on producing and analyzing images in real time. The term can refer to anything from rendering an application's graphical user interface ( GUI) to ...
and
ray tracing, where the mirror-like specular reflection of
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
from other surfaces is often ignored (due to the more intensive computations required to calculate it), and the specular reflection of light directly from point light sources is modeled as specular highlights.
Specular mapping
A
materials system may allow specularity to vary across a surface, controlled by additional layers of
texture maps
Texture mapping is a method for mapping a texture on a computer-generated graphic. Texture here can be high frequency detail, surface texture, or color.
History
The original technique was pioneered by Edwin Catmull in 1974.
Texture mappi ...
.
The early misinterpretation of "Specularity" in computer graphics
Early shaders included a parameter called "Specularity". CG Artists, confused by this term discovered by experimentation that the manipulation of this parameter would cause a reflected highlight from a light source to appear and disappear and therefore misinterpreted "specularity" to mean "light highlights". In fact "Specular" is defined in optics as ''Optics. (of reflected light) directed, as from a smooth, polished surface (opposed to
diffuse ).'' A specular surface is a highly smooth surface. When the surface is very smooth, the reflected highlight is easy to see. As the surface becomes rougher, the reflected highlights gets broader and dimmer. This is a more "diffused" reflection.
In seismology
In the context of
seismic migration, specularity is defined as the cosine of the angle made by the
surface normal
In geometry, a normal is an object such as a line, ray, or vector that is perpendicular to a given object. For example, the normal line to a plane curve at a given point is the (infinite) line perpendicular to the tangent line to the curve ...
vector and the
angle bisector
In geometry, bisection is the division of something into two equal or congruent parts, usually by a line, which is then called a ''bisector''. The most often considered types of bisectors are the ''segment bisector'' (a line that passes through ...
of the angle defined by the directions of the incident and diffracted rays. For a purely specular seismic event the value of specularity should be equal to unity, as the angle between the surface normal vector and the angle bisector should be zero, according to Snell's Law. For a diffractive seismic event, the specularity can be sub-unitary. During the seismic migration, one can filter each seismic event according to the value of specularity, in order to enhance the contribution of
diffractions in the seismic image. Alternatively, the events can be separated in different sub-images according to the value of specularity to produce a
specularity gather.
See also
*
Specular holography
*
Reflection mapping
References
3D computer graphics
Geophysics
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