Lecture 15/16 Lighting/Texture Flashcards
What does pixel colour depend on?
What angle is the ray hitting the geometry?
Where are the light sources?
How strong are the light sources?
What materials are used for primitives?
What does a pure diffuse (“Lambertian”) source do?
A pure diffuse (“Lambertian”) surface scatters light equally in all directions
What does a pure mirror source do?
A pure mirror reflects light along a line symmetrical about the surface normal
Visualise the Lambertian, Phong model and ambient light ray diagrams
What is the most popular lighting model?
The Phong lighting model is the most popular lighting model (also used by OpenGL)
How does the Phong lighting model work?
Based on the light behavior in the real world (but approximation)
- AMBIENT: Ambient term accounts for light scattered equally about entire scene
- DIFFUSE: Dull surfaces have large highlights that fall off more gradually (diffuse)
- SPECULAR: Shiny surfaces have small, intense specular highlights
How does the viewer perceive Diffuse/Lambertian reflection in different positions?
Light is reflected equally in all directions
- the diffuse reflection does not depend on the viewer position
The amount of light on a unit surface depends on what?
- Light from a single source is reflected equally in all directions
- But: amount of light reaching unit surface area depends on the cosine of the angle between the light and the surface (Lambert’s Law)
What is the diffuse term in the lighting model? (Diffuse/Lambertian reflection)
Do this 3 times, for
red, green, and blue.
What does the intensity of the specular highlight depend on?
The intensity of the specular highlight depends on theproximity of the viewing ray to the reflected ray
What is the Specular term in lighting model (Specular reflection: Phong shading)
Do this 3 times, for
red, green, and blue.
What happens when diffuse and specular are combined?
- Diffuse term leads to dull surface
- Specular term leads to shiny surface
What does alpha control in the Phong lighting model?
Shininess effect
What are the consequences of increasing shininess in the Phong lighting model?
- By increasing shininess, the highlight is getting smaller and sharper
- The material thus appears like shinier plastic
How does light scatter in the real world?
Ambient Lighting: Indirect reflections
In the real world, light scatters from object to object
How does the Phong lighting model imitate real world lighting?
Phong lighting adds constant light to fake this ambient lighting
What is the Phong lighting model made up of?
Ambient term creates constant illumination for the entire model
Phong = diffuse + specular + ambient
What is the Standard lighting model?
What is the multi-light Standard lighting model?
What is the multi-light Standard lighting model? (Vector model)
Summary of standard lighting
Comparison of flat, Gouraud and Phong shading
What are the Bidirectional reflectance distribution functions (BRDFs)?
What is Ray tracing / path tracing?
Physically accurate light simulation:
- reflections
- refractions
- soft shadows
- motion blur
- but no caustics or diffuse inter reflections
But … it is very expensive to compute
What are subsurface effects?
Many objects are slightly translucent, such as human skin
What is the limitation of ray tracing?
Ray tracing misses indirect lighting
… “backward” ray tracing is one solution.
… also Ray tracing misses ambient light
What are the limitations of Ray tracing
Ray tracing misses ambient light
… Also Ray tracing misses indirect lighting
How can a brick wall be drawn?
How does texture mapping work?
Texture = image applied to a surface
- Normally 2D, but can also be 1D or 3D
- Require correspondence between pointson surface and in texture
How can texture be mapped onto a spherical shape?
What are the two approaches of texture mapping?
What are the texture map types?
Photos, drawings, or any image
Procedural
What is bump mapping?
Perturb the surface normal
(not the surface colour)
Surface remains flat,
Even though it looks bumpy!
Represent bump mapping with a formula?
Generate the illusion of fine-scale geometry by perturbing the surface normal using a texture
What is displacement mapping?
Perturb the surface height
(not the surface colour)
Surface IS bumpy!
Represent displacement mapping with a formula?
Perturb the surface in the direction of the surface normal
How does backward mapping work?
Surround scene with a sphere
Render scene onto sphere
Colour surface by reflection from the texture
How does a minimap work?
A mipmap consists of a complete set of downsampled images for a given texture
store images of half resolution from the previous level (factor of 2)
How much storage is required for minimaps?
Automatically determine which level of texture to use
- Based on the object’s size on the screen when rendered
Avoids aliasing and saves computation time during renderingat the cost of having to use extra space for the texture
