3.2 Lighting and shading models
3 min read•august 7, 2024
Lighting and shading models are key to creating realistic 3D graphics in AR/VR. They simulate how light interacts with objects, affecting their appearance and mood. Understanding these models is crucial for developers to craft immersive virtual environments.
From basic to advanced , these techniques bring virtual worlds to life. Mastering them allows you to create stunning visuals, from simple diffuse surfaces to complex reflections and shadows, enhancing the user's sense of presence in AR/VR experiences.
Reflection Models
Ambient Light and Diffuse Reflection
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- Ambient light provides a base level of illumination in a scene
- Does not depend on the position or orientation of objects
- Simulates the overall light that bounces around the environment
- describes how rough surfaces scatter light in all directions
- Diffuse reflection depends on the angle between the surface normal and the light direction
- Determines the overall color and brightness of an object (wood, matte plastic)
Specular Reflection and Normal Vectors
- simulates shiny or glossy surfaces that reflect light in a specific direction
- Depends on the viewing angle and the angle between the light direction and the reflection direction
- Creates bright highlights on surfaces (polished metal, shiny plastic)
- Specular highlights are affected by the surface roughness and the light's intensity
- are perpendicular to the surface at each point
- Used to calculate the angle between the surface and the light direction
- Crucial for determining the intensity of diffuse and specular reflections
Shading Techniques
Phong Shading and Gouraud Shading
- calculates the lighting at each pixel, providing more accurate results
- Interpolates the surface normals across the polygon faces
- Performs lighting calculations for each pixel using the interpolated normals
- Produces smooth and realistic shading, but is computationally expensive
- calculates the lighting at each vertex of a polygon
- Interpolates the resulting colors across the polygon face
- Faster than Phong shading but can result in visible color banding artifacts
Shadow Mapping
- is a technique for adding realistic shadows to a scene
- Involves rendering the scene from the light's perspective to create a depth map
- Compares the depth of each pixel from the camera's perspective with the depth map
- If a pixel is further away than the corresponding depth in the map, it is considered to be in shadow
- Allows for self-shadowing and can handle complex scenes with multiple light sources
Advanced Lighting
Global Illumination Techniques
- Global illumination simulates how light bounces around a scene, taking into account both direct and indirect lighting
- is a global illumination method that calculates the transfer of light between surfaces
- Divides surfaces into patches and calculates the energy transfer between them
- Produces diffuse interreflections and soft shadows (interior scenes with matte surfaces)
- simulates the path of light rays as they interact with objects in the scene
- Traces rays from the camera through each pixel and calculates the color based on the objects the rays encounter
- Can accurately simulate reflections, refractions, and shadows (glass, mirrors, transparent objects)
Photon Mapping
- is a two-pass global illumination method
- In the first pass, photons are emitted from light sources and traced through the scene, storing their positions and energies
- In the second pass, the scene is rendered using the stored photons to estimate the indirect illumination
- Combines the accuracy of ray tracing with the efficiency of radiosity
- Can handle complex light transport effects like caustics and subsurface scattering (water, translucent materials)
Key Terms to Review (11)
Ambient light: Ambient light refers to the natural or artificial illumination that fills a scene, creating a baseline level of brightness without a specific source. It serves as the overall light present in an environment, affecting how objects are perceived by softening shadows and illuminating surfaces. This type of light is crucial in creating realistic visuals in computer graphics and simulations, as it helps to establish mood, depth, and spatial relationships.
Diffuse Reflection: Diffuse reflection is the scattering of light rays when they strike a rough or uneven surface, causing the light to be reflected in many different directions. This type of reflection plays a crucial role in how objects are perceived in various lighting conditions, contributing to the overall realism and depth in visual rendering. Unlike specular reflection, which creates clear images and highlights, diffuse reflection results in softer, more uniform lighting on surfaces, impacting shading models significantly.
Global Illumination: Global illumination refers to a group of techniques used in 3D computer graphics to simulate how light interacts with surfaces, accounting for both direct and indirect lighting effects. This approach enhances realism in rendered images by considering how light bounces off surfaces and illuminates other areas, resulting in more accurate shading and color representation. Global illumination is crucial for achieving lifelike visuals, especially in complex environments where light behavior is intricate.
Gouraud Shading: Gouraud shading is a computer graphics shading technique used to simulate the way light interacts with surfaces by interpolating vertex colors across polygons. This method enhances the appearance of 3D models by creating smooth color transitions and reducing the jagged edges often seen with flat shading. By calculating vertex colors based on lighting conditions and then blending them across the surface of the polygon, Gouraud shading provides a more realistic visual experience.
Normal Vectors: Normal vectors are vectors that are perpendicular to a surface at a given point, playing a crucial role in lighting and shading models. They help determine how light interacts with surfaces, which is essential for creating realistic graphics in augmented and virtual reality environments. By using normal vectors, 3D models can accurately simulate the way light reflects, refracts, or absorbs, allowing for better visual representation and depth perception.
Phong Shading: Phong shading is a technique used in 3D computer graphics to simulate the way light interacts with surfaces, creating a realistic appearance by incorporating highlights and shading based on the viewer's perspective. This method enhances the visual quality of objects by calculating the color of each pixel based on ambient, diffuse, and specular reflections, allowing for smooth color transitions and detailed lighting effects. It is widely used in rendering pipelines to achieve a high level of realism in real-time applications.
Photon mapping: Photon mapping is a two-pass global illumination algorithm used in computer graphics to simulate the way light interacts with surfaces, creating realistic lighting and shading effects in 3D environments. It first involves shooting photons from light sources and storing their interactions with surfaces in a spatial data structure, which is then used to calculate the final rendering of the scene. This technique helps to achieve complex lighting phenomena like caustics, color bleeding, and indirect lighting.
Radiosity: Radiosity is a rendering technique used in computer graphics to calculate the diffuse transfer of light between surfaces. It focuses on how light interacts with surfaces in a scene, accounting for both emitted and reflected light. This method is crucial for achieving realistic lighting and shading effects, making it an essential aspect of creating visually convincing virtual environments.
Ray Tracing: Ray tracing is a rendering technique used to simulate the way light interacts with objects to produce realistic images by tracing rays of light as they travel through a scene. This method allows for detailed reflections, refractions, and shadows, making it a critical component in achieving high-quality visual effects in computer graphics. Its connection to advanced rendering techniques enhances lighting accuracy and contributes to the overall realism of virtual environments.
Shadow mapping: Shadow mapping is a computer graphics technique used to create shadows in a scene by determining the areas that are blocked from a light source. This method involves rendering the scene from the perspective of the light source to create a depth map, which is then used to calculate shadows during the final rendering pass. It enhances the realism of lighting effects, making it a crucial aspect of various lighting models and advanced global illumination techniques.
Specular Reflection: Specular reflection is the mirror-like reflection of light from a surface, where the angle of incidence equals the angle of reflection. This phenomenon occurs on smooth surfaces like water, glass, or polished metals, where light rays bounce off uniformly, creating clear and distinct images. It plays a vital role in how surfaces appear in lighting and shading models, affecting the perception of material properties such as glossiness and shininess.