Week 6 - Light and Materials Flashcards
What three things (broadly) can happen when light interacts with a material?
Light is reflected (appears as a mirrored / shiny surfaces with specular highlights or as a flat diffuse surface)
Light can be transmitted through the surface (transparency or refraction)
Light is absorbed by the surface and converted to heat.
Any combination of these may happen all at once
What does reflection look like on a mirrored or shiny surface?
Light is reflected in a single or narrow range of directions
This is normally indicative of a flat surface.
Metal surfaces tend to behave like this, the same electrons that cause magnetism repel the light evenly.
What is diffuse reflection?
When light is reflected scattered in loads of different directions.
The light is penetrating the surface by a tiny amount before reflecting back out. Pure white paper is actually a tangle of fibres and as the light interacts with it it bounces around before being re-emitted.
Instead of one coherent direction the light is reflected in a bunch of random directions.
What kind of reflection leads to a surface with a hard shiny effect, probably with a bright specular highlight?
A combination of diffuse and specular reflection
What part of the rendering equation is modelling the fact that in the real world the perfect lambertian diffuse reflector doesn’t exist?
BRDF
What colour receptor are there far more of than the other two?
Red, there are far more red receptors than green or blue ones.
What do S, M and L wave responses stand for?
Short, Medium and lone wave response
What colour can you not have monochromatic light of?
Purple (The blue and red parts of the spectrum are on opposite sides of the scale) Purple is always an indicator or blue and red light
BRDF = x / y
x = radiance / irradiance
Define radiance
The radiant flux (energy over time) emitted, reflected, transmitted, or received by a given surface, per unit solid angle per unit projected area
What is the name of the device to measure the BRDF of a real material?
goniometer
What law is light refracted according to?
Snell’s Law
What does BTDF stand for?
Bidirectional transmitted distribution function
What does the BTDF describe?
The scattering of light emerging through a material once it has transmitted through it (in the case of transparent / translucent materials). This is similar to the behaviour of the BRDF for reflected light, exiting from the same surface it was incident to
What is sub-surface scattering?
When light bounces around in a material and emerges at a different point and angle from where it entered
