Lighting Models

Question 1

Q1: What is the purpose of lighting models in computer graphics?

Answer 1

A1: To simulate how light interacts with surfaces and determine the color and brightness of each visible point in a rendered image.

Question 2

Q2: What stage of the rendering pipeline does lighting belong to?

Answer 2

A2: After projection and hidden-surface removal — it determines the final appearance of visible surfaces.

Question 3

Q3: What is local illumination?

Answer 3

A3: It only considers direct light from sources to surfaces — no reflections or inter-object lighting.

Question 4

Q4: What is global illumination?

Answer 4

A4: It accounts for all light interactions, including reflections, refractions, and indirect lighting between objects.

Question 5

Q5: Which is more realistic but computationally expensive?

Answer 5

A5: Global illumination.

Question 6

Q6: Which illumination model is commonly used in real-time rendering?

Answer 6

A6: Local illumination (e.g., the Phong model).

Question 7

Q7: What are the three main light source types?

Answer 7

A7: Point light, directional light, and spotlight.

Question 8

Q8: How does a point light behave?

Answer 8

A8: Emits light equally in all directions from a single point in space.

Question 9

Q9: How is a directional light different from a point light?

Answer 9

A9: It has direction but no position — all rays are parallel, like sunlight.

Question 10

Q10: What defines a spotlight?

Answer 10

A10: A point light with a specific cone direction and falloff, simulating focused beams.

Question 11

Q11: What is light attenuation?

Answer 11

A11: The decrease in light intensity with distance from the source — simulates realistic fading.

Question 12

Q12: What are the three components of the Phong lighting model?

Answer 12

A12: Ambient, diffuse, and specular reflection.

Question 13

Q13: What does the ambient component represent?

Answer 13

A13: Indirect light scattered throughout the environment, preventing surfaces from appearing completely black.

Question 14

Q14: What does the diffuse component represent?

Answer 14

A14: Light scattered evenly in all directions on rough surfaces — gives the object its basic color.

Question 15

Q15: What does the specular component represent?

Answer 15

A15: The mirror-like highlight that depends on the viewer’s position relative to the reflection direction.

Question 16

Q16: What kind of surfaces show more specular reflection?

Answer 16

A16: Smooth, shiny materials like plastic, glass, or metal.

Question 17

Q17: What is a Lambertian surface?

Answer 17

A17: A perfectly diffuse surface that appears equally bright from all viewing directions.

Question 18

Q18: What determines the brightness of diffuse reflection?

Answer 18

A18: The angle between the surface normal and the light direction — smaller angles (more perpendicular) appear brighter.

Question 19

Q19: What kind of materials are modeled well by diffuse reflection?

Answer 19

A19: Matte surfaces like chalk, clay, or paper.

Question 20

Q20: What causes a specular highlight on a surface?

Answer 20

A20: Concentrated reflection of light when the viewing direction aligns with the reflected light vector.

Question 21

Q21: What does the shininess (specular exponent) control?

Answer 21

A21: The size and sharpness of the highlight — higher values = smaller, sharper highlight (glossier surface).

Question 22

Q22: Why does specular reflection depend on the viewer’s position?

Answer 22

A22: Because the reflected light must reach the viewer for the highlight to be visible.

Question 23

Q23: How does the Blinn–Phong model improve the original Phong model?

Answer 23

A23: It uses a halfway vector (between light and view directions) instead of a reflection vector, making it more efficient and stable for GPUs.

Question 24

Q24: Which model gives slightly smoother highlights — Phong or Blinn–Phong?

Answer 24

A24: Blinn–Phong.

Question 25

Q25: What is shading?

Answer 25

A25: The process of determining how lighting varies across a surface.

Question 26

Q26: What are the three common shading techniques?

Answer 26

A26: Flat shading, Gouraud shading, and Phong shading.

Question 27

Q27: What is flat shading?

Answer 27

A27: Applies one lighting value per polygon — results in a faceted look.

Question 28

Q28: What is Gouraud shading?

Answer 28

A28: Calculates lighting at vertices and interpolates colors across the surface — smoother but can miss specular highlights.

Question 29

Q29: What is Phong shading?

Answer 29

A29: Interpolates surface normals per pixel and computes lighting per pixel — produces very smooth, realistic highlights.

Question 30

Q30: Which shading method is the most realistic?

Answer 30

A30: Phong shading.

Question 31

Q31: Which shading method is the fastest but least accurate?

Answer 31

A31: Flat shading.

Question 32

Q32: How is object color determined under light?

Answer 32

A32: By multiplying the light’s color by the material’s color component (R, G, B).

Question 33

Q33: Why does a red object under blue light appear black?

Answer 33

A33: Because blue light has no red component to reflect.

Question 34

Q34: What determines whether a material has colored or white highlights?

Answer 34

Metals reflect colored specular highlights (tinted). Non-metals (like plastics) reflect white highlights.

Question 35

Q35: How do multiple light sources affect illumination?

Answer 35

A35: Each light contributes its own ambient, diffuse, and specular components — all are added together for the final color.

Question 36

Q36: Why is the ambient term usually only added once?

Answer 36

A36: Because ambient light represents the global background illumination, not individual light contributions.

Question 37

Q37: Why do we need an ambient term in the lighting model?

Answer 37

A37: Because in real scenes, light bounces around and indirectly illuminates surfaces — ambient light fakes this effect.

Question 38

Q38: Why do matte surfaces appear equally bright from all angles?

Answer 38

A38: Because they scatter light uniformly in every direction.

Question 39

Q39: Why do shiny surfaces have highlights that move as you move your head?

Answer 39

A39: Because specular reflection depends on the viewer’s angle relative to the reflection direction.

Question 40

Q40: Why do we use shading models like Gouraud and Phong?

Answer 40

A40: To smooth out lighting across polygons and avoid visible polygon edges.

Question 41

Q41: Which shading technique can miss specular highlights?

Answer 41

A41: Gouraud shading (because it interpolates vertex colors, not lighting).

Question 42

Q42: Why is the Phong illumination model considered “local”?

Answer 42

A42: It only accounts for direct light from sources — no reflections or refractions between surfaces.