Computer graphics lighting: Difference between revisions

Revision as of 17:44, 17 December 2019

Revision as of 19:46, 5 January 2020

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=== Diffuse ===

Diffuse lighting (or [[diffuse reflection]]) is the direct illumination of an object by an even amount of light interacting with a [[Scattering|light-scattering]] surface<ref name=":83">{{Cite web|url=http://www.bcchang.com/immersive/ygbasics/lighting.html|title=Lighting in 3D Graphics|website=www.bcchang.com|access-date=2019-11-05}}</ref><ref name=":10">{{Cite web|url=http://graphics.cs.cmu.edu/nsp/course/15-462/Spring04/slides/07-lighting.pdf|title=Lighting and Shading|last=Pollard|first=Nancy|date=Spring 2004|website=|url-status=live|archive-url=|archive-date=|access-date=}}</ref>. After light strikes an object, it is reflected as a function of the surface properties of the object as well as the angle of incoming light<ref name=":10" />. This interaction is the primary contributor to the object’sobject's brightness and forms the basis for its color<ref name=":83" />.

=== Ambient ===

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== Illumination models ==

Lighting models are used to replicate lighting effects in [[Rendering (computer graphics)|rendered]] environments where light is approximated based on the physics of light<ref name=":1">{{Cite web|url=https://learnopengl.com/Lighting/Basic-Lighting|title=LearnOpenGL - Basic Lighting|website=learnopengl.com|access-date=2019-11-08}}</ref>. Without lighting models, replicating lighting effects as they occur in the natural world would require more processing power than is practical for computer graphics<ref name=":1" />. This lighting, or illumination model’smodel's purpose is to compute the color of every pixel or the amount of light reflected for different surfaces in the scene<ref>{{Cite web|url=https://www.cs.uic.edu/~jbell/CourseNotes/ComputerGraphics/LightingAndShading.html|title=Intro to Computer Graphics: Lighting and Shading|website=www.cs.uic.edu|access-date=2019-11-08}}</ref>.There are two main illumination models, object oriented lighting and global illumination<ref name=":2">{{Cite web|url=https://www.cc.gatech.edu/classes/AY2003/cs4451a_fall/global-illumination.pdf|title=Global Illumination|last=|first=|date=2002|website=Georgia Tech Classes|url-status=live|archive-url=|archive-date=|access-date=}}</ref>. They differ in that object oriented lighting considers each object individually, whereas global illumination maps how light interacts between objects<ref name=":2" />. Currently, researchers are developing global illumination techniques to more accurately replicate how light interacts with its environment<ref name=":2" />.

=== Object oriented lighting ===

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==== Blinn-Phong illumination model ====

{{Main|Blinn–Phong reflection model}}

The Blinn-Phong illumination model is similar to the Phong model as it uses specular light to create a highlight on an object based on its shininess<ref name=":16">James F. Blinn (1977). "Models of light reflection for computer synthesized pictures". ''Proc. 4th annual conference on computer graphics and interactive techniques'': 192–198. [[CiteSeerX]] 10.1.1.131.7741. {{doi|10.1145/563858.563893}}<br /></ref>. The Blinn-Phong differs from the Phong illumination model, as the Blinn-Phong model uses the vector normal to the surface of the object and halfway between the light source and the viewer<ref name=":1" />. This model is used in order to have accurate specular lighting and reduced computation time<ref name=":1" />.The process takes less time because finding the reflected light vector’svector's direction is a more involved computation than calculating the halfway [[Normal (geometry)|normal vector]] <ref name=":16" />. While this is similar to the Phong model, it produces different visual results, and the specular reflection exponent or shininess might need modification in order to produce a similar specular reflection<ref>Jacob's University, "[http://www.faculty.jacobs-university.de/llinsen/teaching/320322_Fall2010/lecture12.pdf Blinn-Phong Reflection Model]", 2010.</ref>.

=== Global illumination ===

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=== Reflection mapping ===

{{Main articles|Reflection mapping}}

Reflection mapping (also known as environment mapping) is a technique which uses 2D environment maps to create the effect of [[Reflectance|reflectivity]] without using ray tracing<ref name=":5">{{Cite web|url=https://cglearn.codelight.eu/pub/computer-graphics/environment-mapping|title=Computer Graphics: Environment Mapping|website=cglearn.codelight.eu|access-date=2019-11-01}}</ref>. Since the appearances of reflective objects depend on the relative positions of the viewers, the objects, and the surrounding environments, graphics algorithms produce reflection vectors to determine how to color the objects based on these elements<ref>{{Cite web|url=http://web.cse.ohio-state.edu/~wang.3602/courses/cse5542-2013-spring/17-env.pdf|title=Environment Mapping|last=Shen|first=Han-Wei|date=|website=|url-status=live|archive-url=|archive-date=|access-date=}}</ref>. Using 2D environment maps rather than fully- rendered, 3D objects to represent surroundings, reflections on objects can be determined using simple, computationally inexpensive algorithms<ref name=":5" />.

=== Particle systems ===