Editing Global illumination (section)

{{redirect|Realistic rendering|physically-based realistic rendering|Physically-based rendering}}
{{short description|Group of rendering algorithms used in 3D computer graphics}}
{{More citations needed|date=May 2013}}
{{3D computer graphics}}
{{Multiple image|direction=vertical|align=right|image1=Direct lighting.png|image2=Global illumination1.png|width=200|caption1=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.|caption2=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 (optics)|caustic]] projected onto the red wall from light passing through the glass sphere.}}

'''Global illumination'''<ref name="wordpress">{{cite web|url=https://extremeistan.wordpress.com/2014/05/11/realtime-global-illumination-techniques-collection/|title=Realtime Global Illumination techniques collection &#124; extremeistan|date=11 May 2014 |publisher=extremeistan.wordpress.com|access-date=2016-05-14}}</ref> ('''GI'''), or '''indirect illumination''', is a group of [[algorithm]]s used in [[3D computer graphics]] that are meant to add more realistic [[computer graphics lighting|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'').

Theoretically, [[reflection (computer graphics)|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 reflection#Interreflection|diffuse inter-reflection]] or [[caustic (optics)|caustics]] is called global illumination.