Lecture 15/16 Lighting/Texture

Question 1

What does pixel colour depend on?

Answer 1

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?

Question 2

What does a pure diffuse (“Lambertian”) source do?

Answer 2

A pure diffuse (“Lambertian”) surface scatters light equally in all directions

Question 3

What does a pure mirror source do?

Answer 3

A pure mirror reflects light along a line symmetrical about the surface normal

Question 4

Visualise the Lambertian, Phong model and ambient light ray diagrams

Answer 4

Question 5

What is the most popular lighting model?

Answer 5

The Phong lighting model is the most popular lighting model (also used by OpenGL)

Question 6

How does the Phong lighting model work?

Answer 6

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

Question 7

How does the viewer perceive Diffuse/Lambertian reflection in different positions?

Answer 7

Light is reflected equally in all directions
- the diffuse reflection does not depend on the viewer position

Question 8

The amount of light on a unit surface depends on what?

Answer 8

• 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)

Question 9

What is the diffuse term in the lighting model? (Diffuse/Lambertian reflection)

Answer 9

Do this 3 times, for
red, green, and blue.

Question 10

What does the intensity of the specular highlight depend on?

Answer 10

The intensity of the specular highlight depends on theproximity of the viewing ray to the reflected ray

Question 11

What is the Specular term in lighting model (Specular reflection: Phong shading)

Answer 11

Do this 3 times, for
red, green, and blue.

Question 12

What happens when diffuse and specular are combined?

Answer 12

• Diffuse term leads to dull surface
• Specular term leads to shiny surface

Question 13

What does alpha control in the Phong lighting model?

Answer 13

Shininess effect

Question 14

What are the consequences of increasing shininess in the Phong lighting model?

Answer 14

• By increasing shininess, the highlight is getting smaller and sharper
• The material thus appears like shinier plastic

Question 15

How does light scatter in the real world?

Answer 15

Ambient Lighting: Indirect reflections
In the real world, light scatters from object to object

Question 16

How does the Phong lighting model imitate real world lighting?

Answer 16

Phong lighting adds constant light to fake this ambient lighting

Question 17

What is the Phong lighting model made up of?

Answer 17

Ambient term creates constant illumination for the entire model

Phong = diffuse + specular + ambient

Question 18

What is the Standard lighting model?

Answer 18

Question 19

What is the multi-light Standard lighting model?

Answer 19

Question 20

What is the multi-light Standard lighting model? (Vector model)

Answer 20

Question 21

Summary of standard lighting

Answer 21

Question 22

Comparison of flat, Gouraud and Phong shading

Answer 22

Question 23

What are the Bidirectional reflectance distribution functions (BRDFs)?

Answer 23

Question 24

What is Ray tracing / path tracing?

Answer 24

Physically accurate light simulation:
- reflections
- refractions
- soft shadows
- motion blur
- but no caustics or diffuse inter reflections

But … it is very expensive to compute

Question 25

What are subsurface effects?

Answer 25

Many objects are slightly translucent, such as human skin

Question 26

What is the limitation of ray tracing?

Answer 26

Ray tracing misses indirect lighting ... “backward” ray tracing is one solution. ... also Ray tracing misses ambient light

Question 27

What are the limitations of Ray tracing

Answer 27

Ray tracing misses ambient light ... Also Ray tracing misses indirect lighting

Question 28

How can a brick wall be drawn?

Answer 28

Question 29

How does texture mapping work?

Answer 29

Texture = image applied to a surface - Normally 2D, but can also be 1D or 3D - Require correspondence between pointson surface and in texture

Question 30

How can texture be mapped onto a spherical shape?

Answer 30

Question 31

What are the two approaches of texture mapping?

Answer 31

Question 32

What are the texture map types?

Answer 32

Photos, drawings, or any image Procedural

Question 33

What is bump mapping?

Answer 33

Perturb the surface normal (not the surface colour) Surface remains flat, Even though it looks bumpy!

Question 34

Represent bump mapping with a formula?

Answer 34

Generate the illusion of fine-scale geometry by perturbing the surface normal using a texture

Question 35

What is displacement mapping?

Answer 35

Perturb the surface height (not the surface colour) Surface IS bumpy!

Question 36

Represent displacement mapping with a formula?

Answer 36

Perturb the surface in the direction of the surface normal

Question 37

How does backward mapping work?

Answer 37

Surround scene with a sphere Render scene onto sphere Colour surface by reflection from the texture

Question 38

How does a minimap work?

Answer 38

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)

Question 39

How much storage is required for minimaps?

Answer 39

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