Global illumination

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Direct lighting.png
Rendering without global illumination. Areas that lie outside of the ceiling lamp's direct light lack definition. For example, the lamp's housing appears completely uniform. Without the ambient light added into the render, it would appear uniformly black.
Global illumination1.png
Rendering with global illumination. Light is reflected by surfaces, and colored light transfers from one surface to another. Notice how color from the red wall and green wall (not visible) reflects onto other surfaces in the scene. Also notable is the caustic projected onto the red wall from light passing through the glass sphere.

Global illumination [1] (GI), or indirect illumination, is a group of algorithms used in 3D computer graphics that are meant to add more realistic lighting to 3D scenes. Such algorithms take into account not only the light that comes directly from a light source (direct illumination), but also subsequent cases in which light rays from the same source are reflected by other surfaces in the scene, whether reflective or not (indirect illumination).

Contents

Theoretically, reflections, refractions, and shadows are all examples of global illumination, because when simulating them, one object affects the rendering of another (as opposed to an object being affected only by a direct source of light). In practice, however, only the simulation of diffuse inter-reflection or caustics is called global illumination.

Algorithms

Images rendered using global illumination algorithms often appear more photorealistic than those using only direct illumination algorithms. However, such images are computationally more expensive and consequently much slower to generate. One common approach is to compute the global illumination of a scene and store that information with the geometry (e.g., radiosity). The stored data can then be used to generate images from different viewpoints for generating walkthroughs of a scene without having to go through expensive lighting calculations repeatedly.

Radiosity, ray tracing, beam tracing, cone tracing, path tracing, volumetric path tracing, Metropolis light transport, ambient occlusion, photon mapping, signed distance field and image-based lighting are all examples of algorithms used in global illumination, some of which may be used together to yield results that are not fast, but accurate.

These algorithms model diffuse inter-reflection which is a very important part of global illumination; however most of these (excluding radiosity) also model specular reflection, which makes them more accurate algorithms to solve the lighting equation and provide a more realistically illuminated scene. The algorithms used to calculate the distribution of light energy between surfaces of a scene are closely related to heat transfer simulations performed using finite-element methods in engineering design.

Photorealism

Exterior view of an architectural model Alexexterior2.jpg
Exterior view of an architectural model
Example of an ambient occlusion layer Show how 3D real time ambient occlusion works 2013-11-23 10-45.jpeg
Example of an ambient occlusion layer

Achieving accurate computation of global illumination in real-time remains difficult. [2] In real-time 3D graphics, the diffuse inter-reflection component of global illumination is sometimes approximated by an "ambient" term in the lighting equation, which is also called "ambient lighting" or "ambient color" in 3D software packages. Though this method of approximation (also known as a "cheat" because it's not really a global illumination method) is easy to perform computationally, when used alone it does not provide an adequately realistic effect. Ambient lighting is known to "flatten" shadows in 3D scenes, making the overall visual effect more bland. However, used properly, ambient lighting can be an efficient way to make up for a lack of processing power.

Procedure

More and more specialized algorithms are used in 3D programs that can effectively simulate the global illumination. These algorithms are numerical approximations to the rendering equation. Well known algorithms for computing global illumination include path tracing, photon mapping and radiosity. The following approaches can be distinguished here:

In Light-path notation global lighting the paths of the type L (D | S) corresponds * E.

A full treatment can be found in [3]

Image-based lighting

Another way to simulate real global illumination is the use of high-dynamic-range images (HDRIs), also known as environment maps, which encircle and illuminate the scene. This process is known as image-based lighting.

List of methods

MethodDescription/Notes
Ray tracing Several enhanced variants exist for solving problems related to sampling, aliasing, and soft shadows: Distributed ray tracing, cone tracing, and beam tracing.
Path tracing Unbiased, variant: Bi-directional path tracing and energy redistribution path tracing [4]
Photon mapping Consistent, biased; enhanced variants: Progressive photon mapping, stochastic progressive photon mapping ( [5] )
Lightcuts Enhanced variants: Multidimensional lightcuts and bidirectional lightcuts [6]
Point based global illumination Extensively used in movie animations [7] [8]
Radiosity Finite element method, very good for precomputations. Improved versions are instant radiosity [9] and bidirectional instant radiosity [10]
Metropolis light transport Builds upon bi-directional path tracing, unbiased, and multiplexed [11]
Spherical harmonic lighting Encodes global illumination results for real-time rendering of static scenes
Ambient occlusion -
Voxel-based global illuminationSeveral variants exist, including voxel cone tracing global illumination, [12] sparse voxel octree global illumination, and voxel global illumination (VXGI) [13]
Light propagation volumes global illumination [14] Light propagation volumes is a technique to approximately achieve global illumination (GI) in real-time.

It uses lattices and spherical harmonics (SH) to represent the spatial and angular distribution of light in the scene. Variant cascaded light propagation volumes. [15]

Deferred radiance transfer global illumination [16]
Deep G-buffer based global illumination [17]
Signed Distance Fields Dynamic Diffuse Global Illumination [18]
Global Illumination Based on Surfels [19]

See also

Related Research Articles

<span class="mw-page-title-main">Rendering (computer graphics)</span> Process of generating an image from a model

Rendering or image synthesis is the process of generating a photorealistic or non-photorealistic image from a 2D or 3D model by means of a computer program. The resulting image is referred to as the render. Multiple models can be defined in a scene file containing objects in a strictly defined language or data structure. The scene file contains geometry, viewpoint, texture, lighting, and shading information describing the virtual scene. The data contained in the scene file is then passed to a rendering program to be processed and output to a digital image or raster graphics image file. The term "rendering" is analogous to the concept of an artist's impression of a scene. The term "rendering" is also used to describe the process of calculating effects in a video editing program to produce the final video output.

<span class="mw-page-title-main">Radiosity (computer graphics)</span> Computer graphics rendering method using diffuse reflection

In 3D computer graphics, radiosity is an application of the finite element method to solving the rendering equation for scenes with surfaces that reflect light diffusely. Unlike rendering methods that use Monte Carlo algorithms, which handle all types of light paths, typical radiosity only account for paths which leave a light source and are reflected diffusely some number of times before hitting the eye. Radiosity is a global illumination algorithm in the sense that the illumination arriving on a surface comes not just directly from the light sources, but also from other surfaces reflecting light. Radiosity is viewpoint independent, which increases the calculations involved, but makes them useful for all viewpoints.

<span class="mw-page-title-main">Ray tracing (graphics)</span> Rendering method

In 3D computer graphics, ray tracing is a technique for modeling light transport for use in a wide variety of rendering algorithms for generating digital images.

Metropolis light transport (MLT) is a global illumination application of a variant of the Monte Carlo method called the Metropolis–Hastings algorithm to the rendering equation for generating images from detailed physical descriptions of three-dimensional scenes.

In computer graphics, photon mapping is a two-pass global illumination rendering algorithm developed by Henrik Wann Jensen between 1995 and 2001 that approximately solves the rendering equation for integrating light radiance at a given point in space. Rays from the light source and rays from the camera are traced independently until some termination criterion is met, then they are connected in a second step to produce a radiance value. The algorithm is used to realistically simulate the interaction of light with different types of objects. Specifically, it is capable of simulating the refraction of light through a transparent substance such as glass or water, diffuse interreflection between illuminated objects, the subsurface scattering of light in translucent materials, and some of the effects caused by particulate matter such as smoke or water vapor. Photon mapping can also be extended to more accurate simulations of light, such as spectral rendering. Progressive photon mapping (PPM) starts with ray tracing and then adds more and more photon mapping passes to provide a progressively more accurate render.

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Shading refers to the depiction of depth perception in 3D models or illustrations by varying the level of darkness. Shading tries to approximate local behavior of light on the object's surface and is not to be confused with techniques of adding shadows, such as shadow mapping or shadow volumes, which fall under global behavior of light.

<span class="mw-page-title-main">Ray casting</span> Methodological basis for 3D CAD/CAM solid modeling and image rendering

Ray casting is the methodological basis for 3D CAD/CAM solid modeling and image rendering. It is essentially the same as ray tracing for computer graphics where virtual light rays are "cast" or "traced" on their path from the focal point of a camera through each pixel in the camera sensor to determine what is visible along the ray in the 3D scene. The term "Ray Casting" was introduced by Scott Roth while at the General Motors Research Labs from 1978–1980. His paper, "Ray Casting for Modeling Solids", describes modeled solid objects by combining primitive solids, such as blocks and cylinders, using the set operators union (+), intersection (&), and difference (-). The general idea of using these binary operators for solid modeling is largely due to Voelcker and Requicha's geometric modelling group at the University of Rochester. See solid modeling for a broad overview of solid modeling methods. This figure on the right shows a U-Joint modeled from cylinders and blocks in a binary tree using Roth's ray casting system in 1979.

<span class="mw-page-title-main">Lightmap</span> Data structure used in lightmapping

A lightmap is a data structure used in lightmapping, a form of surface caching in which the brightness of surfaces in a virtual scene is pre-calculated and stored in texture maps for later use. Lightmaps are most commonly applied to static objects in applications that use real-time 3D computer graphics, such as video games, in order to provide lighting effects such as global illumination at a relatively low computational cost.

<span class="mw-page-title-main">Rendering equation</span> Integral equation

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<span class="mw-page-title-main">Path tracing</span> Computer graphics method

Path tracing is a computer graphics Monte Carlo method of rendering images of three-dimensional scenes such that the global illumination is faithful to reality. Fundamentally, the algorithm is integrating over all the illuminance arriving to a single point on the surface of an object. This illuminance is then reduced by a surface reflectance function (BRDF) to determine how much of it will go towards the viewpoint camera. This integration procedure is repeated for every pixel in the output image. When combined with physically accurate models of surfaces, accurate models of real light sources, and optically correct cameras, path tracing can produce still images that are indistinguishable from photographs.

In computer graphics, per-pixel lighting refers to any technique for lighting an image or scene that calculates illumination for each pixel on a rendered image. This is in contrast to other popular methods of lighting such as vertex lighting, which calculates illumination at each vertex of a 3D model and then interpolates the resulting values over the model's faces to calculate the final per-pixel color values.

Light transport theory deals with the mathematics behind calculating the energy transfers between media that affect visibility. This article is currently specific to light transport in rendering processes such as global illumination and HDRI.

<span class="mw-page-title-main">3D rendering</span> Process of converting 3D scenes into 2D images

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Computer graphics lighting is the collection of techniques used to simulate light in computer graphics scenes. While lighting techniques offer flexibility in the level of detail and functionality available, they also operate at different levels of computational demand and complexity. Graphics artists can choose from a variety of light sources, models, shading techniques, and effects to suit the needs of each application.

<span class="mw-page-title-main">Kerkythea</span> Standalone rendering system

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<span class="mw-page-title-main">Hemicube (computer graphics)</span> Computer graphics technique

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This is a glossary of terms relating to computer graphics.

References

  1. ↑ "Realtime Global Illumination techniques collection | extremeistan". extremeistan.wordpress.com. 11 May 2014. Retrieved 2016-05-14.
  2. ↑ Kurachi, Noriko (2011). The Magic of Computer Graphics. CRC Press. p. 339. ISBN   9781439873571 . Retrieved 24 September 2017.
  3. ↑ Dutre, Philip; Bekaert, Philippe; Bala, Kavita (2006). Advanced Global Illumination (2nd ed.). ISBN   978-1568813073.
  4. ↑ Cline, D.; Talbot, J.; Egbert, P. (2005). "Energy redistribution path tracing". ACM Transactions on Graphics. 24 (3): 1186–95. doi:10.1145/1073204.1073330.
  5. ↑ "Toshiya Hachisuka at UTokyo". ci.i.u-tokyo.ac.jp. Retrieved 2016-05-14.
  6. ↑ Walter, Bruce; Fernandez, Sebastian; Arbree, Adam; Bala, Kavita; Donikian, Michael; Greenberg, Donald P. (1 July 2005). "Lightcuts". ACM Transactions on Graphics. 24 (3): 1098–1107. doi:10.1145/1073204.1073318.
  7. ↑ "coursenote.dvi" (PDF). Graphics.pixar.com. Archived (PDF) from the original on 2011-08-17. Retrieved 2016-12-02.
  8. ↑ Daemen, Karsten (November 14, 2012). "Point Based Global Illumination An introduction [Christensen, 2010]" (PDF). KU Leuven. Archived from the original (PDF) on 2014-12-22.
  9. ↑ "Instant Radiosity: Keller (SIGGRAPH 1997)" (PDF). Cs.cornell.edu. Archived (PDF) from the original on 2012-06-18. Retrieved 2016-12-02.
  10. ↑ Segovia, B.; Iehl, J.C.; Mitanchey, R.; Péroche, B. (2006). "Bidirectional instant radiosity" (PDF). Rendering Techniques. Eurographics Association. pp. 389–397. Archived from the original (PDF) on 2016-01-30.
  11. ↑ Hachisuka, T.; Kaplanyan, A.S.; Dachsbacher, C. (2014). "Multiplexed metropolis light transport" (PDF). ACM Transactions on Graphics. 33 (4): 1–10. doi:10.1145/2601097.2601138. S2CID   79980. Archived from the original (PDF) on 2015-09-23.
  12. ↑ Cyril Crassin. "Voxel Cone Tracing and Sparse Voxel Octree for Real-time Global Illumination" (PDF). On-demand.gputechconf.com. Archived (PDF) from the original on 2013-09-03. Retrieved 2016-12-02.
  13. ↑ "VXGI | GeForce". geforce.com. 8 April 2015. Retrieved 2016-05-14.
  14. ↑ "Light Propagation Volumes GI - Epic Wiki". wiki.unrealengine.com. Retrieved 2016-05-14.
  15. ↑ Engelhardt, T.; Dachsbacher, C. (2009). "Granular visibility queries on the GPU" (PDF). Proceedings of the 2009 symposium on Interactive 3D graphics and games. pp. 161–7. doi:10.1145/1507149.1507176. ISBN   978-1-60558-429-4. S2CID   14841843. Archived from the original (PDF) on 2016-01-18.
  16. ↑ "Deferred Radiance Transfer Volumes: Global Illumination in Far Cry 3" (PDF). Twvideo01.ubm-us.net. Archived (PDF) from the original on 2014-09-06. Retrieved 2016-12-02.
  17. ↑ "Fast Global Illumination Approximations on Deep G-Buffers". graphics.cs.williams.edu. Archived from the original on 2016-02-21. Retrieved 2016-05-14.
  18. ↑ Hu, Jinkai; K. Yip, Milo; Elias Alonso, Guillermo; Shi-hao, Gu; Tang, Xiangjun; Xiaogang, Jin (2020). "Signed Distance Fields Dynamic Diffuse Global Illumination". arXiv: 2007.14394 [cs.GR].
  19. ↑ "Global Illumination Based on Surfels". SIGGRAPH. Retrieved 2021-12-02.
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