Lighting in 3D Modelling and Games

Lighting in 3D Modelling, Games, and Multimedia

• Lighting is essential for computer visualization.
• Without lighting, 3D models are not visible.
• Physical light models are computationally intensive and simplified in computer graphics.
• Advancements in computer technology have led to more realistic illumination models.

Illumination Description

• Illumination is described by position (in some light geometries) and orientation.
• Key features are:
  • Light source(s) present in the scene.
  • Material properties of the illuminated surfaces.

Light Source

• A light source can be treated as another object in the scene.
• Features to define a light source include:
  • Intensity: the strength of the light emitted.
  • Color: the color of the light emitted.
  • Geometry: the shape of the light source (e.g., directional, point, spotlight, area, volume).

Light Source - Geometry

• Directional light: simulated at infinity, defined by a single vector that represents its direction (e.g., the sun).
• Point light: located within the 3D scene, specified by its 3D position (e.g., a lamp).
• Spotlight: produces direct light through a cone, defined by 3D position, direction and drop-off (e.g., a flashlight).
• Area light: emits directional light rays from an area shape (e.g., a rectangle or circle, like a fluorescent ceiling light).
• Volume light: similar to point light, but a specific shape and size (e.g., beams of light through an open window).
• Ambient light: emits soft light rays in all directions; simulates indirect light (used to fill areas without direct light).

Specular vs Diffuse

• Light reflection depends on object surface properties, light source, and direction.
• Specular reflection: occurs from smooth surfaces (e.g., mirrors, calm water).
• Diffuse reflection: occurs from rough surfaces (e.g., clothing, asphalt).
• The observer position is irrelevant for diffuse reflection.

Highlight

• Highlights are localized specular reflections on smooth materials.

Local vs Global Shading

• Local illumination models only consider direct light.
• Global illumination models consider both direct and indirect light (e.g., reflected or transmitted light).

Shading

• The normal of a facet/polygon is a key factor in shading models.
• Initial shading algorithms calculated the normal for every point on a surface.
• This is computationally expensive, so methodologies were developed to optimize the process.

Constant Shading

• Constant shading uses the same color for the entire polygon.
• This method works well when the light source is infinitely far away and the observer is also far from the scene, but isn't suitable for curved surfaces or where lighting variations are needed.

Advantages and Disadvantages of Constant Shading

• Advantages: Easy to implement, computationally inexpensive.
• Disadvantages: Can produce unrealistic results in certain situations, e.g., noticeable edges between polygons creating a faceted appearance.

Interpolated Shading

• Interpolated shading methods were developed to smooth the transitions between polygons in the shading effect (e.g., in curved surfaces).
• The approach is to use information from adjacent polygons.

Gouraud Shading

• Calculates vertex shading values by averaging normals of the vertices.
• Interpolates initial values to determine shading intensities (colors) of the polygon facets.

Gouraud Shading: Advantages and Disadvantages

• Advantages: Efficient and relatively easy to implement.
• Disadvantages: Highlights will not appear within a polygon and highlights present in a vertex are scattered into a bigger area (unrealistic).

Phong Shading

• Interpolates normals of vertices.
• Calculates lighting based on the interpolated normals (more accurate than Gouraud method).

Phong Shading: Advantages and Disadvantages

• Advantages: Good results with specular surfaces, display highlights within polygons, and produces more realistic results when showcasing highlights.
• Disadvantages: Interpolated normals require normalization prior to shading calculations.

Global Illumination Models

• Global illumination models consider indirect light (e.g., reflected or transmitted light) in addition to direct light.
• This approach produces more realistic results in computer graphics.

Ray Tracing

• A technique originating in lens making, where rays are traced to simulate how light interacts with objects in a scene.
• Rays are cast from the viewer to object surfaces to determine the light path, enabling the computer to compute details like shadows and reflections.
• This method allows for more realistic rendering.

Ray Tracing: Advantages and Disadvantages

• Advantages: Produces good results in scenes with specular surfaces and well-lit environments.
• Disadvantages: Computationally expensive making it slow, requires recalculation if the viewer or light source position changes.

Radiosity

• A global illumination method based on thermal radiation between surfaces.
• Calculates the amount of light energy transferred between surfaces based on the diffuse rays bouncing off objects.
• Radiosity is useful in interior scenes and for simulating color bleeding.
• Independent of viewer position, so viewer movements don't require recalculation.

Radiance

• An illumination model developed to compute radiometric quantities more accurately.
• Emphasizes the properties of incoming and outgoing light (radiance and irradiance).
• Often used to create high-dynamic-range (HDR) photorealistic images.

Lumen

• A new ray-tracing global illumination model that runs in real-time and creates realistic scenarios.
• Specifically useful for dynamic scenarios using Unreal Engine 5.