How does simulation software achieves realistic images and lighting environment? This article explains the principles of global illumination, as a starting point for further details on how Ocean™ is accurately replicating light interactions and materials optical behavior for virtual prototyping uses.
Through precise rendering techniques, Ocean™ optical simulation software, delivers digital product samples that look and behave like their real-world counterparts. It significantly reduces development time by enabling fast iteration processes. The result is a reliable, high quality render or set of data.
What is global illumination?
Global illumination rendering software simulates the complex interplay of light within a 3D scene. It takes into account both direct and indirect light, resulting in more realistic images.
Direct illumination
Direct illumination is the light that travels directly from a source to an object without any intermediate interactions. This type of illumination is straightforward but forms the basis for more complex lighting models. It is a commonly used method for CGI applications.
Direct illumination casts sharp, well-defined shadows behind objects. The length and direction of the shadow depend on the position of the light source and the object.
Specular highlights are bright spots formed when light hits a shiny surface and reflects directly towards the viewer, indicating the surface’s reflective properties and the light source’s position and intensity.
Lighting intensity decreases with distance from the source following an inverse-square law, essential for creating realistic depth and spatial relationships in a scene.
Direct illumination can create distinct lighting effects based on the directionality of the light source. For example, a spotlight focuses light in a specific direction, creating intense illumination in targeted areas while leaving others in shadow.
Figure 1: Direct illumination is the light that arrives directly from the emitter.
Indirect illumination
Indirect illumination includes other light contributions such as diffuse and specular reflections, color mixing, caustics and subsurface scattering. The object appearance results from both direct light but also accounts for rays that have been reflected or scattered by other surfaces in the scene.
Light that bounces off surfaces and diffuses in multiple directions, contributing to the overall light distribution in a scene.
Mirror-like reflections where light bounces off a surface at a single angle, creating sharp highlights and glossy effects.
The phenomenon where light reflecting off a colored surface carries the surface color to adjacent areas, subtly tinting them.
Focused patterns of light formed when light rays are refracted through transparent materials like water or glass, or reflected from shiny surfaces.
When light penetrates a translucent material it scatters internally, and then exits the material at a different point, giving objects a soft, glowing appearance.
These components of indirect illumination contribute to the realism of rendered scenes as it accounts for the complex ways light interacts with various materials and surfaces.
Figure 2: Indirect illumination includes several light contributions, generating more accurate render.
Consider a car interior lit by sunlight streaming through the window. Traditional rendering might only account for the direct sunlight hitting the dashboard. However, in reality, light bounces off the seats, floor, and other surfaces, subtly illuminating the shadowed areas of the dashboard and resulting in a more nuanced and realistic lighting effect. This is precisely what global illumination rendering software such as Ocean™ captures.
Figure 3: Simulation generated with Ocean™ illustrating areas such as footrest or start & stop button, illuminated by indirect lighting.
The basics of global lighting
Main approaches
At its core, global illumination relies on algorithms that trace the path of light particles (photons) as they travel through a scene. There are three main approaches:
- Ray tracing: This method shoots rays out from the virtual camera and simulates how they interact with objects in the scene. When a ray hits an object, the software calculates how much light is reflected, absorbed, or transmitted, and then determines where the reflected or transmitted rays travel next. This process continues until the rays are no longer strong enough to contribute to the final image.
Figure 4: Ray tracing method shoots rays out from the virtual camera and simulates how they interact with objects in the scene
Ray tracing technology encompasses a variety of methods for creating realistic renders. From video games to reliable images for R&D use in material science, the applications are wide. The rigorous scientific approach of Ocean™ and its computational capabilities enable the implementation of techniques such as Bidirectional Path Tracing to produce accurate images based on the physics of light and materials.
For more details on ray tracing, see: Our introduction to ray tracing techniques and our comparison with the path tracing technologies used by Ocean™.
- Radiosity: This approach divides the scene into smaller patches and calculates how much light is emitted and reflected by each patch. The software then iteratively computes the light exchange between all the patches until a stable equilibrium is reached, representing the final illumination of the scene.
Figure 5: Radiosity divides the scene into smaller patches and calculates how much light is emitted and reflected by each patch.
- Photon mapping: Photon mapping is another technique used in global illumination rendering. It involves emitting photons from a light source and simulating their interactions within the scene. These interactions are stored in a point-based data structure called a photon map, which is later used to estimate the lighting at various points in the scene. A key aspect of photon mapping is sampling, which refers to the process of strategically selecting a specific number of photons to trace.
Figure 6: Photon mapping involves emitting photons from a light source and simulating their interactions within the scene.
Comparing global illumination techniques:
These 3 main approaches have advantages and disadvantages which are listed in the figure below. Eclat Digital, with its Ocean™ virtual prototyping software, uses ray tracing, making it a highly valuable tool for generating predictive images and data suitable for a wide range of applications where accuracy in appearance is required.
Figure 7: Performance comparison of global illumination techniques
Why use Global Illumination software?
By simulating these light interactions, realistic rendering software using global illumination, such as Ocean™ creates a more physically accurate representation of how light behaves in a real-world environment. This is particularly important for scientific applications where material properties and lighting effects need to be precisely predicted. The ability to produce highly realistic digital product samples through rendering is an asset for decision-making processes in product design and engineering. It significantly reduces development time by enabling fast iteration processes.
In a future article, we will explore Ocean™’s ability to use global illumination to generate physically true virtual prototypes that can be relied upon for development process, showcasing how real-world accuracy is achieved through advanced rendering techniques.
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