11 - Lighting

ucla | CS 174A | 2024-03-18 22:08

Types of lighting

ambient - instead of checking the physical scattering, we assume each object has ambient lighting directly behind it that gives us a silhoutte
diffuse - reveals shape of obj based on diffusivity of light across the surface of the object
specular - shine, shows specualr highlights of the light soruces
Ambient Lighting
background light - estimates true scattering
does NOT depend on position/direction, object, or eye
Diffuse Lighting
point source light
lambertian (diffuse) reflection for dull matte surfaces -> looks equally bright from all directions
reflect light equally in all directions
Lambert’s law: light intensity is prop to direction
N is the normal from/to the surface
L is the light vector (surface to light source)
$\theta$ is angle between N,L
Specular Lighting
shiny surfaces
color of light matters (included in point light intensity) not color of object
depends on position of light, object and eye
R is the reflection vector from the surface
V is the view/eye/cam vector from the surface
$f_{att}$ is attenuation factor: see Final Lighting
$\phi$ is angle between R and V

$\vec R=2(\vec N\cdot\vec L)\vec N\space-\space\vec L$

halfway vector $\vec H$ is halfway b/w L and V = norm(L+V)
replace $(R\cdot V)^n$ with $(H\cdot N)^n$
s.t. $(H\cdot N)^n=\cos^n\Psi\quad :\quad \Psi=\phi/2$
Final Lighting
$I_\lambda=\bigg(k_{a\lambda}*I_{a\lambda}\bigg)*O_{d\lambda}\space+\space \bigg(f_{att}*k_{d\lambda}*I_{p\lambda}*(N\cdot L)\bigg)*O_{d\lambda}\space+\space\bigg(f_{att}*k_{s\lambda}*I_{d\lambda}*(R\cdot V)^n\bigg)$ where $\lambda\in{R,G,B}$
Incident Angle
angle is angle bw norm to surface and light source
$\theta\lt 90$ => some light based on angle
$\theta=90$ => max light
$\theta > 90$ => self-occlusion, no light
Directional light sources
if light is far enough away
L is the same (constant) for the entire scene for all objects
N is the same for the entire polygon
thus $N\cdot L$ is constant on the poly
Attenuated Light source
diffuse light reflected off object
d is the distance of the light to the object
Colored Light Sources
OBJECT COLOR (not light color)
object’s diffuse color $O_{d\lambda}\in{O_{dR},O_{dG},O_{dB}}$
split into R,G,B components
thus final term => (ambient + diffuse term) * $O_{d\lambda}$
Fog: Atmospheric Attenuation and Blending
Misc Improvements