Why Specular reflected light will be in bright color(usually white) while other parts of the object are reflecting the perceived color wavelength?
Reflection off of smooth surfaces such as mirrors or a calm body of water leads to a type of reflection known as specular reflection. Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway leads to a type of reflection known as diffuse reflection.
Specular reflection occurs for all polished and smooth surfaces, like mirrors. The angle of reflection in specular reflection is equal to the angle of incidence. Rough or unpolished surfaces are not good specular reflectors as they do not reflect light at the same angle as the angle of incidence.
To produce specular reflection, surface irregularities need to be smaller than the length of the beam's radiation, such as in the case of polished metal, glass, plastic or transparent liquid surfaces. On a “perfect” surface, the angle of beam radiation is equivalent to that of the incident radiation.
A familiar example of specular reflectance is provided by a plane mirror, in which the angles of light incidence and reflectance are equal. An ideal mirror reflects all incident light nonselectively with wavelength.
From a physical perspective, this is because:
Say you have a piece of red plastic with a smooth surface. The plastic is red because it contains a red dye or pigment. Incoming light that enters the plastic tends to be reflected if red, or absorbed if it is not; this red light bounces around inside the plastic and makes it back out in a more or less random direction (which is why this component is called "diffuse").
On the other hand, some of the incoming light never makes it into the plastic to begin with: it bounces off the surface, instead. Because the surface of the plastic is smooth, its direction is not randomized: it reflects off in a direction based on the mirror reflection angle (which is why it is called "specular"). Since it never hits any of the colorant in the plastic, its color is not changed by selective absorption like the diffuse component; this is why specular reflection is usually white.
I should add that the above is a highly simplified version of reality: there are plenty of cases that are not covered by these two possibilities. However, they are common enough and generally applicable enough for computer graphics work: the diffuse+specular model can give a good visible approximation to many surfaces, especially when combined with other cheap approximation like bump mapping, etc.
Edit: a reference in response to Ayappa's comment -- the mechanism that generally gives rise to specular highlights is called Fresnel reflection. It is a classical phenomenon, depending solely on the refractive index of the material.
If the surface of the material is optically smooth (e.g., a high-quality glass window), the Fresnel reflection will produce a true mirror-like image. If the material is only partly smooth (like semigloss paint) you will get a specular highlight, which may be narrow or wide based on how smooth it is at the microscopic level. If the material is completely rough (either at a microscopic level or at some larger scale which is smaller than your image resolution), then the Fresnel reflection becomes effectively diffuse, and cannot be readily distinguished from other forms of diffuse reflection.
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