Using the phong reflectance model, the strength of the specular highlight is…
2019
Using the phong reflectance model, the strength of the specular highlight is determined by the angle between
- A.
the view vector and the normal vector
- B.
the light vector and the normal vector
- C.
the light vector and the reflected vector
- D.
the reflected vector and the view vector
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Correct answer: D
Answer: The strength of the specular highlight is determined by the angle between the reflected vector and the view vector.
Key formula: the Phong specular term is proportional to (R · V)^s, where R is the reflection of the light vector about the surface normal, V is the view vector (both unit length), and s is the shininess exponent. Larger s produces tighter, sharper highlights.
Compute the reflection vector: R = 2 (N · L) N − L (assuming unit vectors).
Evaluate the dot product between R and V: cos θ = max(R · V, 0).
Raise cos θ to the shininess exponent: specular = k_s * (cos θ)^s, where k_s is the specular coefficient.
Note: The Blinn-Phong variant uses the halfway vector H = normalize(L + V) and computes (N · H)^s as an efficient and often visually similar approximation to the original Phong term.