Editing Rendering (computer graphics) (section)

===Photorealistic rendering===
A large proportion of [[computer graphics]] research has worked towards producing images that resemble photographs. Fundamental techniques that make this possible were invented in the 1980s, but at the end of the decade, photorealism for complex scenes was still considered a distant goal.{{r|IntroToRTPreface|p=x}} Today, photorealism is routinely achievable for offline rendering, but remains difficult for [[Real-time computer graphics|real-time rendering]].{{r|RealTimeRayTracing|pp=1-2}}

In order to produce realistic images, rendering must simulate how light travels from light sources, is reflected, refracted, and scattered (often many times) by objects in the scene, passes through a camera lens, and finally reaches the film or sensor of the camera. The physics used in these simulations is primarily [[geometrical optics]], in which [[Photon|particles of light]] follow (usually straight) lines called  ''[[Ray (optics)|rays]]'', but in some situations (such as when rendering [[Thin-film interference|thin films]], like the surface of [[soap bubble]]s) the [[Electromagnetic radiation|wave nature of light]] must be taken into account.{{r|Pharr2023_1_2}}{{r|Pharr2023_9fr_wo}}

Effects that may need to be simulated include:
* [[Shadow]]s, including both shadows with sharp edges and ''[[Umbra, penumbra and antumbra|soft shadows]]'' with umbra and penumbra
* [[Reflection (computer graphics)|Reflections]] in mirrors and smooth surfaces, as well as rough or rippled reflective surfaces
* [[Refraction]]{{snd}} the bending of light when it crosses a boundary between two transparent materials such as air and glass. The amount of bending varies with the wavelength of the light, which may cause colored fringes or "rainbows" to appear.
* Volumetric effects{{snd}} Absorption and scattering when light travels through partially transparent or translucent substances (called ''participating media'' because they modify the light rather than simply allow rays to pass through){{r|Christensen2016|p=140}}{{r|Pharr2023_1_2}}
* [[Caustic (optics)|Caustics]]{{snd}} bright patches, sometimes with distinct filaments and a folded or twisted appearance, resulting when light is reflected or refracted before illuminating an object.{{r|Christensen2016|p=109}}

In realistic scenes, objects are illuminated both by light that arrives directly from a light source (after passing mostly unimpeded through air), and light that has bounced off other objects in the scene. The simulation of this complex lighting is called [[global illumination]]. In the past, indirect lighting was often faked (especially when rendering [[Computer animation|animated films]]) by placing additional hidden lights in the scene, but today [[path tracing]] is used to render it accurately.{{r|Veach1997|p=3}}{{r|Christensen2016|p=108}}

For true photorealism, the camera used to take the photograph must be simulated. The ''[[Thin lens|thin lens approximation]]'' allows combining [[3D projection#Perspective projection|perspective projection]] with [[depth of field]] (and [[bokeh]]) emulation. [[Camera lens]] simulations can be made more realistic by modeling the way light is refracted by the components of the lens. [[Motion blur]] is often simulated if film or video frames are being rendered.{{r|Pharr2023_1_2}}{{r|Pharr2023_5_2}} Simulated [[lens flare]] and [[Bloom (shader effect)|bloom]] are sometimes added to make the image appear subjectively brighter (although the design of real cameras tries to reduce these effects).{{r|AkenineMöller2018|loc=12.4}}

Realistic rendering uses mathematical descriptions of how different surface materials reflect light, called ''[[reflectance]] models'' or (when physically plausible) ''[[Bidirectional reflectance distribution function|bidirectional reflectance distribution functions (BRDFs)]]''.{{r|Pharr2023_1_2}} Rendering materials such as [[Marble sculpture|marble]], plant leaves, and human skin requires simulating an effect called [[subsurface scattering]], in which a portion of the light travels into the material, is scattered, and then travels back out again.{{r|Christensen2016|p=143}} The way color, and properties such as [[Surface roughness|roughness]], vary over a surface can be represented efficiently using [[texture mapping]].{{r|AkenineMöller2018|loc=6.1}}