Concerning phong shading and Gouraud shading in scene, which of
2020
Concerning phong shading and Gouraud shading in a 3D scene, which of the following statements are true?
(A) Gouraud shading requires more computation than phong shading
(B) Gouraud shading linearly interpolates the color of an interior pixel from the color at the vertices
(C) Phong shading interpolates over the normal vectors specified at the vertices
Choose the correct answer from the options given below:
- A.
(A) and (B) Only
- B.
(A) and (C) Only
- C.
(B) and (C) Only
- D.
(A), (B) and (C)
Attempted by 16 students.
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Correct answer: C
Answer: The statements "Gouraud shading linearly interpolates the color of an interior pixel from the color at the vertices" and "Phong shading interpolates over the normal vectors specified at the vertices" are correct; the statement that "Gouraud shading requires more computation than Phong shading" is incorrect.
Gouraud shading:
Compute lighting at each vertex using the lighting model, then linearly interpolate the resulting vertex colors across the interior of the polygon for each pixel.
Because lighting is evaluated only at vertices, Gouraud is generally less computationally expensive than Phong, but it can miss or soften small specular highlights that don't lie on vertices.
Phong shading:
Interpolate the vertex normal vectors across the surface (per-fragment), normalize the interpolated normals, and evaluate the lighting model at each pixel using those normals.
This produces more accurate per-pixel lighting and better specular highlights, but it requires more per-pixel computation than Gouraud.
Conclusion: The correct combination is the two true statements about color interpolation in Gouraud and normal interpolation in Phong; the computational claim about Gouraud being more expensive is false.