Specular Reflection and the Phong Model.
When we look at an illuminated shiny surface, such as polished metal we see a highlight, or bright spot, at certain viewing directions. Moreover, This phenomenon is called specular reflections, is the result of the total, or near total reflection of the incident light in a concentrated region around the specular reflection angle.
- Moreover, The figure shows specular reflections direction at a point on the illuminated surface. The specular reflection angle equals the angle of the incident light.
- Here we use R as a unit vector in direction of reflection L is unit vector point towards light vector N is unit normal vector and V is the unit vector in viewing direction.
- Also, Objects other than ideal reflectors exhibits specular reflections over a finite range of viewing positions around vector R. Shiny surface have a narrow specular reflection range and dull surface have wide specular reflection range.
- By Phong, specular reflection model or simply Phong model sets the intensity of specular reflections proportional to 𝑐𝑜𝑠𝑛𝑠∅. The angle varies in between 00 to 900.
- Also, Values assigned to specular reflections parameter ns determined by the type of surface that we want to display. A shiny surface assigned ns values large nearly 100 and dull surface assigned small nearly 1.
- The intensity of specular reflections depends on the material properties of the surface and the angle of incidence as well as specular reflection coefficient, (𝜽) for each surface.
The specular reflections is given by 𝐼𝑠𝑝𝑒𝑐 = 𝑤(𝜃)𝐼𝑙𝑐𝑜𝑠𝑛𝑠∅
- Where 𝐼𝑙 the intensity of light source and is an angle between viewing direction V and specular reflection direction R.
- Since the angle between two unit vector V and R we can put 𝑐𝑜𝑠∅ = 𝑉 ∙ 𝑅.
- Also, And also for many surfaces (𝜃) is constant so we take specular reflection constant as Ks so the equation becomes:
- 𝐼𝑠𝑝𝑒𝑐 = 𝐾𝑠𝐼𝑙(𝑉 ∙ 𝑅)𝑛𝑠
- Vector r calculated in terms of vector L and N as shown in figure
- Fig. Calculation of vector R by considering projection onto the direction of the normal vector N.
- 𝑅 + 𝐿 = (2𝑁 ∙ 𝐿)
- 𝑅 = (2𝑁 ∙ 𝐿)− 𝐿
- Moreover, Somewhat simplified Phong model is to calculate between halfway vectors H and use product of H and N instead of V and R.
- Here H calculated as follow: H = (L+V)/ (|L+V|)