G7: Shading Models Flashcards
What is a shading model?
A computational model used to determine the color (shade) of visible surfaces in a scene.
What are the two types of illumination models used in shading?
Local illumination: Uses only direct light at a point
Global illumination: Accounts for light transport from the entire scene
Which shading model type is typically used in rasterization pipelines?
Local illumination
What three factors does local illumination depend on?
Light sources
Local surface geometry & material
Camera viewpoint
What does radiometry measure?
The amount of light energy (photon activity) using terms like radiant energy, flux, and irradiance.
What is irradiance?
Energy received per unit area per unit time.
(Unit: W/m²)
What equation relates energy in a photon to its wavelength?
Q=(hc)/λ
Where:
h = Planck’s constant
c = speed of light
λ = wavelength
What is Lambert’s cosine law?
For diffuse surfaces, color is proportional to max(0,dot(N,L))
(N = surface normal, L = light direction)
Why is max(0,dot(N,L)) used in Lambertian shading?
To avoid negative light contributions when the surface faces away from the light.
List four common light types in graphics.
Ambient light
Directional light
Point light
Spotlight
What’s unique about point lights?
They emit light equally in all directions, and their irradiance falls off with 1/(r^2).
What is the Phong reflection model formula?
ca = ka⋅La
cd = kd/(d^2) ⋅ max(0,dot(N,L))⋅Ld
cs = ks/(d^2) ⋅ max(0,dot(R,V))^shininess ⋅ Ls
What is the Blinn-Phong model?
A modified Phong model using a halfway vector H between light and view instead of computing R (reflection).
Compare flat, Gouraud, and Phong shading.
Flat shading: Evaluate illumination once per polygon.
Gouraud shading: Evaluate at vertices, interpolate color.
Phong shading: Interpolate normals, evaluate illumination per pixel.
