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    TERM PAPER

    OF

    COMPUTER

    GRAPHICS

    TOPIC: HARDWARE RENDERING

    SUBMITTED TO: - SUBMITTED BY:-

    DR.UMESH SEHGAL VISHAL PATYAL

    ROLL NO. 03

    CLASS:-BT MT CSE

    SECTION- C

    REG.NO-3050060122

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    ABSTRACT

    As we know this is new introduction of term paper which is nothing but

    minor project in networking in which i deeply studied about ATM

    NETWORKS which is very helpful to us in the future in the field of IT

    industry. In this project I made ATM (asynchronous transfer mode) which

    is a dedicated-connection switching technology that organizes digital data

    into 53- byte cell units and transmits them over a physical medium using

    digital signal technology ATM networks are made up of three distinct

    elements: users (endpoint devices), switches, and interfaces.

    http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci211721,00.htmlhttp://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci211761,00.htmlhttp://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci211761,00.htmlhttp://searchstorage.techtarget.com/sDefinition/0,,sid5_gci211721,00.html
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    Contents:-

    An introduction to computer graphics

    Rendering

    1 Usage 2 Features 3 Techniques

    o 3.1 Scan line rendering and rasterisation o 3.2 Ray casting o 3.3 Radiosity o 3.4 Ray tracing

    4 Optimisation o 4.1 Optimizations used by an artist when a scene is being

    developed o 4.2 Common optimizations for real time rendering

    5 Sampling and filtering 6 Academic core

    o 6.1 The rendering equation o 6.2 The Bidirectional Reflectance Distribution Function o 6.3 Geometric optics o 6.4 Visual perception o Bibliography

    http://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Usage%23Usagehttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Features%23Featureshttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Techniques%23Techniqueshttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Scanline_rendering_and_rasterisation%23Scanline_rendering_and_rasterisationhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Ray_casting%23Ray_castinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Radiosity%23Radiosityhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Ray_tracing%23Ray_tracinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Optimisation%23Optimisationhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Optimizations_used_by_an_artist_when_a_scene_is_being_developed%23Optimizations_used_by_an_artist_when_a_scene_is_being_developedhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Optimizations_used_by_an_artist_when_a_scene_is_being_developed%23Optimizations_used_by_an_artist_when_a_scene_is_being_developedhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Common_optimizations_for_real_time_rendering%23Common_optimizations_for_real_time_renderinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Sampling_and_filtering%23Sampling_and_filteringhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Academic_core%23Academic_corehttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#The_rendering_equation%23The_rendering_equationhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#The_Bidirectional_Reflectance_Distribution_Function%23The_Bidirectional_Reflectance_Distribution_Functionhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Geometric_optics%23Geometric_opticshttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Visual_perception%23Visual_perceptionhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Usage%23Usagehttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Features%23Featureshttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Techniques%23Techniqueshttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Scanline_rendering_and_rasterisation%23Scanline_rendering_and_rasterisationhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Ray_casting%23Ray_castinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Radiosity%23Radiosityhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Ray_tracing%23Ray_tracinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Optimisation%23Optimisationhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Optimizations_used_by_an_artist_when_a_scene_is_being_developed%23Optimizations_used_by_an_artist_when_a_scene_is_being_developedhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Optimizations_used_by_an_artist_when_a_scene_is_being_developed%23Optimizations_used_by_an_artist_when_a_scene_is_being_developedhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Common_optimizations_for_real_time_rendering%23Common_optimizations_for_real_time_renderinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Sampling_and_filtering%23Sampling_and_filteringhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Academic_core%23Academic_corehttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#The_rendering_equation%23The_rendering_equationhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#The_Bidirectional_Reflectance_Distribution_Function%23The_Bidirectional_Reflectance_Distribution_Functionhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Geometric_optics%23Geometric_opticshttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#Visual_perception%23Visual_perception
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    An introduction to computer graphics:-

    Computers have become a powerful tool for the rapid and economical production of pictures. There is virtually no area in which graphical

    displays cannot be used to some advantages, and so it is so notsurprising to find the use of computer graphics so widespread. Althoughearly applications in engineering and science had to rely on expensiveand cumbersome equipment, advances in computer technology havemade interactive computer graphics a practical tool. Today, we findcomputer graphics used routinely in such diverse areas as science,engineering, medicine, business, industry, government, art,entertainment, advertising, education, and training. Before we get intothe details of how to do computer graphics, we first take a short tour through a gallery of graphics applications.

    Computer aided designPresentation graphicsComputer artEntertainmentEducation and trainingVisualizationImage processingGraphics user interface

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    Render ing ( comp uter gr aphi cs) : -

    Rendering is the process of generating an image from a model , by means of computer programs. The model is a description of three-dimensional objectsin a strictly defined language or data structure. It would contain geometry,viewpoint, texture , lighting , and shading information. The image is a digital image or raster graphics image . The term may be by analogy with an "artist'srendering" of a scene. 'Rendering' is also used to describe the process of calculating effects in a video editing file to produce final video output.

    It is one of the major sub-topics of 3D computer graphics , and in practicealways connected to the others. In the graphics pipeline , it is the last major step, giving the final appearance to the models and animation. With theincreasing sophistication of computer graphics since the 1970s onward, ithas become a more distinct subject.

    Rendering has uses in architecture , video games , simulators , movie or TVspecial effects , and design visualization, each employing a different balance

    of features and techniques. As a product, a wide variety of renderers areavailable. Some are integrated into larger modeling and animation packages,some are stand-alone, some are free open-source projects. On the inside, arenderer is a carefully engineered program, based on a selective mixture of disciplines related to: light physics , visual perception , mathematics , andsoftware development .

    In the case of 3D graphics, rendering may be done slowly, as in pre-rendering , or in real time. Pre-rendering is a computationally intensive

    process that is typically used for movie creation, while real-time rendering is

    often done for 3D video games which rely on the use of graphics cards with3D hardware accelerators.

    Usage :-

    When the pre-image (a wireframe sketch usually) is complete, rendering isused, which adds in bitmap textures or procedural textures , lights, bump

    http://en.wikipedia.org/wiki/3D_modelhttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Raster_graphicshttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/3D_computer_graphicshttp://en.wikipedia.org/wiki/Graphics_pipelinehttp://en.wikipedia.org/wiki/Architectural_renderinghttp://en.wikipedia.org/wiki/Video_gamehttp://en.wikipedia.org/wiki/Simulationhttp://en.wikipedia.org/wiki/Filmhttp://en.wikipedia.org/wiki/Visual_effectshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Visual_systemhttp://en.wikipedia.org/wiki/Mathematicshttp://en.wikipedia.org/wiki/Software_engineeringhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Wireframe_modelhttp://en.wikipedia.org/wiki/Bitmap_textureshttp://en.wikipedia.org/wiki/Procedural_textureshttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/3D_modelhttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Raster_graphicshttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/3D_computer_graphicshttp://en.wikipedia.org/wiki/Graphics_pipelinehttp://en.wikipedia.org/wiki/Architectural_renderinghttp://en.wikipedia.org/wiki/Video_gamehttp://en.wikipedia.org/wiki/Simulationhttp://en.wikipedia.org/wiki/Filmhttp://en.wikipedia.org/wiki/Visual_effectshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Visual_systemhttp://en.wikipedia.org/wiki/Mathematicshttp://en.wikipedia.org/wiki/Software_engineeringhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Wireframe_modelhttp://en.wikipedia.org/wiki/Bitmap_textureshttp://en.wikipedia.org/wiki/Procedural_textureshttp://en.wikipedia.org/wiki/Bump_mapping
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    mapping , and relative position to other objects. The result is a completedimage the consumer or intended viewer sees.

    For movie animations, several images (frames) must be rendered, andstitched together in a program capable of making an animation of this sort.Most 3D image editing programs can do this.

    A rendered image can be understood in terms of a number of visiblefeatures. Rendering research and development has been largely motivated byfinding ways to simulate these efficiently. Some relate directly to particular algorithms and techniques, while others are produced together.

    Features : -

    shading how the color and brightness of a surface varies withlighting

    texture-mapping a method of applying detail to surfaces bump-mapping a method of simulating small-scale bumpiness on

    surfaces fogging/participating medium how light dims when passing

    through non-clear atmosphere or air shadows the effect of obstructing light soft shadows varying darkness caused by partially obscured light

    sources reflection mirror-like or highly glossy reflection transparency , transparency or opacity sharp transmission of light

    through solid objects translucency highly scattered transmission of light through solid

    objects refraction bending of light associated with transparency diffraction bending, spreading and interference of light passing by

    an object or aperture that disrupts the ray indirect illumination surfaces illuminated by light reflected off

    other surfaces, rather than directly from a light source (also known asglobal illumination)

    caustics (a form of indirect illumination) reflection of light off ashiny object, or focusing of light through a transparent object, to

    produce bright highlights on another object

    http://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Distance_foghttp://en.wikipedia.org/wiki/Shadowhttp://en.wikipedia.org/wiki/Soft_shadowshttp://en.wikipedia.org/wiki/Reflection_(computer_graphics)http://en.wikipedia.org/wiki/Transparency_(optics)http://en.wikipedia.org/wiki/Transparency_(graphic)http://en.wikipedia.org/wiki/Opacity_(optics)http://en.wikipedia.org/wiki/Translucencyhttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Global_illuminationhttp://en.wikipedia.org/wiki/Caustic_(optics)http://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Distance_foghttp://en.wikipedia.org/wiki/Shadowhttp://en.wikipedia.org/wiki/Soft_shadowshttp://en.wikipedia.org/wiki/Reflection_(computer_graphics)http://en.wikipedia.org/wiki/Transparency_(optics)http://en.wikipedia.org/wiki/Transparency_(graphic)http://en.wikipedia.org/wiki/Opacity_(optics)http://en.wikipedia.org/wiki/Translucencyhttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Global_illuminationhttp://en.wikipedia.org/wiki/Caustic_(optics)
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    depth of field objects appear blurry or out of focus when too far infront of or behind the object in focus

    motion blur objects appear blurry due to high-speed motion, or themotion of the camera

    non-photorealistic rendering rendering of scenes in an artisticstyle, intended to look like a painting or drawing

    Te chni qu es : -

    Many rendering algorithms have been researched, and software used for rendering may employ a number of different techniques to obtain a finalimage.

    Tracing every ray of light in a scene is impractical and would take an

    enormous amount of time. Even tracing a portion large enough to producean image takes an inordinate amount of time if the sampling is notintelligently restricted.

    Therefore, four loose families of more-efficient light transport modellingtechniques have emerged: rasterisation , including scanline rendering ,geometrically projects objects in the scene to an image plane, withoutadvanced optical effects; ray casting considers the scene as observed from aspecific point-of-view, calculating the observed image based only ongeometry and very basic optical laws of reflection intensity, and perhapsusing Monte Carlo techniques to reduce artifacts; radiosity uses finite element mathematics to simulate diffuse spreading of light from surfaces;and ray tracing is similar to ray casting, but employs more advanced opticalsimulation, and usually uses Monte Carlo techniques to obtain more realisticresults at a speed that is often orders of magnitude slower.

    1. Most advanced software combines two or more of the techniques toobtain good-enough results at reasonable cost. ^ http://portal.acm.org/citation.cfm?

    id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDE

    Pharr; Humphreys (2004). Physically Based Rendering . MorganKaufmann. ISBN 0-12-553180-X .

    http://en.wikipedia.org/wiki/Depth_of_fieldhttp://en.wikipedia.org/wiki/Motion_blurhttp://en.wikipedia.org/wiki/Non-photorealistic_renderinghttp://en.wikipedia.org/wiki/Rasterizationhttp://en.wikipedia.org/wiki/Scanline_renderinghttp://en.wikipedia.org/wiki/Ray_castinghttp://en.wikipedia.org/wiki/Monte_Carlo_methodhttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Ray_tracinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#cite_ref-0%23cite_ref-0http://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDEhttp://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDEhttp://en.wikipedia.org/wiki/Special:BookSources/012553180Xhttp://en.wikipedia.org/wiki/Depth_of_fieldhttp://en.wikipedia.org/wiki/Motion_blurhttp://en.wikipedia.org/wiki/Non-photorealistic_renderinghttp://en.wikipedia.org/wiki/Rasterizationhttp://en.wikipedia.org/wiki/Scanline_renderinghttp://en.wikipedia.org/wiki/Ray_castinghttp://en.wikipedia.org/wiki/Monte_Carlo_methodhttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Ray_tracinghttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#cite_ref-0%23cite_ref-0http://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDEhttp://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDEhttp://en.wikipedia.org/wiki/Special:BookSources/012553180X
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    Shirley; Morley (2003). Realistic Ray Tracing (2nd ed.). AK Peters.ISBN 1-56881-198-5 .

    Dutre; Bala; Bekaert (2002). Advanced Global Illumination . AK Peters. ISBN 1-56881-177-2 .

    Akenine-Moller; Haines (2002). Real-time Rendering (2nd ed.). AK Peters. ISBN 1-56881-182-9 . Strothotte; Schlechtweg (2002). Non-Photorealistic Computer

    Graphics . Morgan Kaufmann. ISBN 1-55860-787-0 . Gooch; Gooch (2001). Non-Photorealistic Rendering . AKPeters.

    ISBN 1-56881-133-0 . Jensen (2001). Realistic Image Synthesis Using Photon Mapping . AK

    Peters. ISBN 1-56881-147-0 . Blinn (1996). Jim Blinns Corner - A Trip Down The Graphics

    Pipeline . Morgan Kaufmann. ISBN 1-55860-387-5 . Glassner (1995). Principles Of Digital Image Synthesis . Morgan

    Kaufmann. ISBN 1-55860-276-3 . Cohen; Wallace (1993). Radiosity and Realistic Image Synthesis . AP

    Professional. ISBN 0-12-178270-0 . Foley; Van Dam; Feiner; Hughes (1990). Computer Graphics:

    Principles And Practice . Addison Wesley. ISBN 0-201-12110-7 . Glassner (ed.) (1989). An Introduction To Ray Tracing . Academic

    Press. ISBN 0-12-286160-4 . Description of the 'Radiance' system

    Though it receives less attention, an understanding of human visual perception is valuable to rendering. This is mainly because image displaysand human perception have restricted ranges. A renderer can simulate analmost infinite range of light brightness and color, but current displays movie screen, computer monitor, etc. cannot handle so much, andsomething must be discarded or compressed. Human perception also haslimits, and so doesn't need to be given large-range images to create realism.This can help solve the problem of fitting images into displays, and,furthermore, suggest what short-cuts could be used in the rendering

    simulation, since certain subtleties won't be noticeable. This related subjectis tone mapping .

    Mathematics used in rendering includes: linear algebra , calculus , numerical mathematics , signal processing , monte carlo .

    http://en.wikipedia.org/wiki/Special:BookSources/1568811985http://en.wikipedia.org/wiki/Special:BookSources/1568811772http://en.wikipedia.org/wiki/Special:BookSources/1568811829http://en.wikipedia.org/wiki/Special:BookSources/1558607870http://en.wikipedia.org/wiki/Special:BookSources/1568811330http://en.wikipedia.org/wiki/Special:BookSources/1568811470http://en.wikipedia.org/wiki/Special:BookSources/1558603875http://en.wikipedia.org/wiki/Andrew_Glassnerhttp://en.wikipedia.org/wiki/Special:BookSources/1558602763http://en.wikipedia.org/wiki/Special:BookSources/0121782700http://en.wikipedia.org/wiki/Special:BookSources/0201121107http://en.wikipedia.org/wiki/Special:BookSources/0122861604http://radsite.lbl.gov/radiance/papers/sg94.1/http://en.wikipedia.org/wiki/Tone_mappinghttp://en.wikipedia.org/wiki/Linear_algebrahttp://en.wikipedia.org/wiki/Calculushttp://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Digital_signal_processinghttp://en.wikipedia.org/wiki/Monte_Carlo_methodhttp://en.wikipedia.org/wiki/Special:BookSources/1568811985http://en.wikipedia.org/wiki/Special:BookSources/1568811772http://en.wikipedia.org/wiki/Special:BookSources/1568811829http://en.wikipedia.org/wiki/Special:BookSources/1558607870http://en.wikipedia.org/wiki/Special:BookSources/1568811330http://en.wikipedia.org/wiki/Special:BookSources/1568811470http://en.wikipedia.org/wiki/Special:BookSources/1558603875http://en.wikipedia.org/wiki/Andrew_Glassnerhttp://en.wikipedia.org/wiki/Special:BookSources/1558602763http://en.wikipedia.org/wiki/Special:BookSources/0121782700http://en.wikipedia.org/wiki/Special:BookSources/0201121107http://en.wikipedia.org/wiki/Special:BookSources/0122861604http://radsite.lbl.gov/radiance/papers/sg94.1/http://en.wikipedia.org/wiki/Tone_mappinghttp://en.wikipedia.org/wiki/Linear_algebrahttp://en.wikipedia.org/wiki/Calculushttp://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Digital_signal_processinghttp://en.wikipedia.org/wiki/Monte_Carlo_method
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    Rendering for movies often takes place on a network of tightly connectedcomputers known as a render farm .

    The current state of the art in 3-D image description for movie creation isthe Mental Ray scene description language designed at mental images andthe RenderMan shading language designed at Pixar . (compare with simpler 3D fileformats such as VRML or APIs such as OpenGL and DirectX tailored for 3D hardware accelerators).

    Other renderers (including proprietary ones) can and are sometimes used, but most other renderers tend to miss one or more of the often neededfeatures like good texture filtering, texture caching, programmable shaders,highend geometry types like hair, subdivision or nurbs surfaces withtesselation on demand, geometry caching, raytracing with geometry caching,

    high quality shadow mapping, speed or patent-free implementations. Other highly sought features these days may include IPR and hardwarerendering/shading.

    Rendering is practically exclusively concerned with the particle aspect of light physics known as geometric optics. Treating light, at its basic level,as particles bouncing around is a simplification, but appropriate: the waveaspects of light are negligible in most scenes, and are significantly moredifficult to simulate. Notable wave aspect phenomena include diffraction as seen in the colours of CDs and DVDs and polarisation as seen inLCDs . Both types of effect, if needed, are made by appearance-orientedadjustment of the reflection model.

    The Bidirectional Reflectance Distribution Function (BRDF) expresses asimple model of light interaction with a surface as follows:

    Light interaction is often approximated by the even simpler models: diffusereflection and specular reflection, although both can be BRDFs.

    This is the key academic/theoretical concept in rendering. It serves as themost abstract formal expression of the non-perceptual aspect of rendering.All more complete algorithms can be seen as solutions to particular formulations of this equation.

    Meaning: at a particular position and direction, the outgoing light (L o) is thesum of the emitted light (L e) and the reflected light. The reflected light beingthe sum of the incoming light (L i) from all directions, multiplied by the

    http://en.wikipedia.org/wiki/Render_farmhttp://en.wikipedia.org/wiki/State_of_the_arthttp://en.wikipedia.org/wiki/Mental_Rayhttp://en.wikipedia.org/w/index.php?title=Scene_description_language&action=edit&redlink=1http://en.wikipedia.org/wiki/Mental_imageshttp://en.wikipedia.org/wiki/RenderManhttp://en.wikipedia.org/wiki/Shading_languagehttp://en.wikipedia.org/wiki/Pixarhttp://en.wikipedia.org/wiki/VRMLhttp://en.wikipedia.org/wiki/Application_programming_interfacehttp://en.wikipedia.org/wiki/OpenGLhttp://en.wikipedia.org/wiki/DirectXhttp://en.wikipedia.org/w/index.php?title=Interactive_Photorealistic_Rendering&action=edit&redlink=1http://en.wikipedia.org/wiki/Compact_dischttp://en.wikipedia.org/wiki/DVDhttp://en.wikipedia.org/wiki/Liquid_crystal_displayhttp://en.wikipedia.org/wiki/Bidirectional_Reflectance_Distribution_Functionhttp://en.wikipedia.org/wiki/Render_farmhttp://en.wikipedia.org/wiki/State_of_the_arthttp://en.wikipedia.org/wiki/Mental_Rayhttp://en.wikipedia.org/w/index.php?title=Scene_description_language&action=edit&redlink=1http://en.wikipedia.org/wiki/Mental_imageshttp://en.wikipedia.org/wiki/RenderManhttp://en.wikipedia.org/wiki/Shading_languagehttp://en.wikipedia.org/wiki/Pixarhttp://en.wikipedia.org/wiki/VRMLhttp://en.wikipedia.org/wiki/Application_programming_interfacehttp://en.wikipedia.org/wiki/OpenGLhttp://en.wikipedia.org/wiki/DirectXhttp://en.wikipedia.org/w/index.php?title=Interactive_Photorealistic_Rendering&action=edit&redlink=1http://en.wikipedia.org/wiki/Compact_dischttp://en.wikipedia.org/wiki/DVDhttp://en.wikipedia.org/wiki/Liquid_crystal_displayhttp://en.wikipedia.org/wiki/Bidirectional_Reflectance_Distribution_Function
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    surface reflection and incoming angle. By connecting outward light toinward light, via an interaction point, this equation stands for the whole'light transport' all the movement of light in a scene.

    The implementation of a realistic renderer always has some basic element of physical simulation or emulation some computation which resembles or abstracts a real physical process.

    The term " physically-based " indicates the use of physical models andapproximations that are more general and widely accepted outsiderendering. A particular set of related techniques have gradually becomeestablished in the rendering community.

    The basic concepts are moderately straightforward, but intractable to

    calculate; and a single elegant algorithm or approach has been elusive for more general purpose renderers. In order to meet demands of robustness,accuracy, and practicality, an implementation will be a complexcombination of different techniques.

    Rendering research is concerned with both the adaptation of scientificmodels and their efficient application.

    One problem that any rendering system must deal with, no matter whichapproach it takes, is the sampling problem . Essentially, the rendering

    process tries to depict a continuous function from image space to colors byusing a finite number of pixels. As a consequence of the Nyquist theorem ,the scanning frequency must be twice the dot rate, which is proportional toimage resolution . In simpler terms, this expresses the idea that an imagecannot display details smaller than one pixel.

    If a naive rendering algorithm is used, high frequencies in the imagefunction will cause ugly aliasing to be present in the final image. Aliasingtypically manifests itself as jaggies , or jagged edges on objects where the

    pixel grid is visible. In order to remove aliasing, all rendering algorithms (if they are to produce good-looking images) must filter the image function toremove high frequencies, a process called antialiasing .

    For real-time, it is appropriate to simplify one or more commonapproximations, and tune to the exact parameters of the scenery in question,which is also tuned to the agreed parameters to get the most 'bang for the

    buck'.

    http://en.wikipedia.org/wiki/Continuous_functionhttp://en.wikipedia.org/wiki/Nyquist-Shannon_sampling_theoremhttp://en.wikipedia.org/wiki/Image_resolutionhttp://en.wikipedia.org/wiki/Aliasinghttp://en.wikipedia.org/wiki/Jaggieshttp://en.wikipedia.org/wiki/Antialiasinghttp://en.wikipedia.org/wiki/Continuous_functionhttp://en.wikipedia.org/wiki/Nyquist-Shannon_sampling_theoremhttp://en.wikipedia.org/wiki/Image_resolutionhttp://en.wikipedia.org/wiki/Aliasinghttp://en.wikipedia.org/wiki/Jaggieshttp://en.wikipedia.org/wiki/Antialiasing
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    Due to the large number of calculations, a work in progress is usually onlyrendered in detail appropriate to the portion of the work being developed ata given time, so in the initial stages of modeling, wireframe and ray castingmay be used, even where the target output is ray tracing with radiosity. It is

    also common to render only parts of the scene at high detail, and to removeobjects that are not important to what is currently being developed.

    Spiral Sphere and Julia, Detail , a computer-generated image created byvisual artist Robert W. McGregor using only POV-Ray 3.6 and its built-in

    scene description language.

    Ray tracing is an extension of the same technique developed in scanlinerendering and ray casting. Like those, it handles complicated objects well,and the objects may be described mathematically. Unlike scanline andcasting, ray tracing is almost always a Monte Carlo technique that is one

    based on averaging a number of randomly generated samples from a model.

    In this case, the samples are imaginary rays of light intersecting theviewpoint from the objects in the scene. It is primarily beneficial wherecomplex and accurate rendering of shadows, refraction or reflection areissues.

    In a final, production quality rendering of a ray traced work, multiple raysare generally shot for each pixel, and traced not just to the first object of intersection, but rather, through a number of sequential 'bounces', using the

    http://en.wikipedia.org/wiki/POV-Rayhttp://en.wikipedia.org/wiki/Ray_tracinghttp://en.wikipedia.org/wiki/Image:SpiralSphereAndJuliaDetail1.jpghttp://en.wikipedia.org/wiki/POV-Rayhttp://en.wikipedia.org/wiki/Ray_tracing
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    In advanced radiosity simulation, recursive, finite-element algorithms'bounce' light back and forth between surfaces in the model, until somerecursion limit is reached. The colouring of one surface in this wayinfluences the colouring of a neighbouring surface, and vice versa. The

    resulting values of illumination throughout the model (sometimes includingfor empty spaces) are stored and used as additional inputs when performingcalculations in a ray-casting or ray-tracing model.

    Due to the iterative/recursive nature of the technique, complex objects are particularly slow to emulate. Prior to the standardization of rapid radiositycalculation, some graphic artists used a technique referred to loosely as false radiosity by darkening areas of texture maps corresponding to corners, jointsand recesses, and applying them via self-illumination or diffuse mapping for scanline rendering. Even now, advanced radiosity calculations may be

    reserved for calculating the ambiance of the room, from the light reflectingoff walls, floor and celiing, without examining the contribution that complexobjects make to the radiosity -- or complex objects may be replaced in theradiosity calculation with simpler objects of similar size and texture.

    If there is little rearrangement of radiosity objects in the scene, the sameradiosity data may be reused for a number of frames, making radiosity aneffective way to improve on the flatness of ray casting, without seriouslyimpacting the overall rendering time-per-frame.

    Because of this, radiosity has become the leading real-time renderingmethod, and has been used from beginning-to-end to create a large number of well-known recent feature-length animated 3D-cartoon films.

    Rendering is the process of generating an image from a model , by means of computer programs. The model is a description of three-dimensional objectsin a strictly defined language or data structure. It would contain geometry,viewpoint, texture , lighting , and shading information. The image is a digital image or raster graphics image . The term may be by analogy with an "artist's

    rendering" of a scene. 'Rendering' is also used to describe the process of calculating effects in a video editing file to produce final video output.

    It is one of the major sub-topics of 3D computer graphics , and in practicealways connected to the others. In the graphics pipeline , it is the last major step, giving the final appearance to the models and animation. With the

    http://en.wikipedia.org/wiki/False_radiosityhttp://en.wikipedia.org/wiki/False_radiosityhttp://en.wikipedia.org/wiki/3D_modelhttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Raster_graphicshttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/3D_computer_graphicshttp://en.wikipedia.org/wiki/Graphics_pipelinehttp://en.wikipedia.org/wiki/False_radiosityhttp://en.wikipedia.org/wiki/False_radiosityhttp://en.wikipedia.org/wiki/3D_modelhttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Digital_imagehttp://en.wikipedia.org/wiki/Raster_graphicshttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/3D_computer_graphicshttp://en.wikipedia.org/wiki/Graphics_pipeline
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    increasing sophistication of computer graphics since the 1970s onward, ithas become a more distinct subject.

    Rendering has uses in architecture , video games , simulators , movie or TVspecial effects , and design visualization, each employing a different balanceof features and techniques. As a product, a wide variety of renderers areavailable. Some are integrated into larger modeling and animation packages,some are stand-alone, some are free open-source projects. On the inside, arenderer is a carefully engineered program, based on a selective mixture of disciplines related to: light physics , visual perception , mathematics , andsoftware development .

    In the case of 3D graphics, rendering may be done slowly, as in pre-rendering , or in real time. Pre-rendering is a computationally intensive

    process that is typically used for movie creation, while real-time rendering isoften done for 3D video games which rely on the use of graphics cards with3D hardware accelerators.

    When the pre-image (a wireframe sketch usually) is complete, rendering isused, which adds in bitmap textures or procedural textures , lights, bump mapping , and relative position to other objects. The result is a completedimage the consumer or intended viewer sees.

    For movie animations, several images (frames) must be rendered, and

    stitched together in a program capable of making an animation of this sort.Most 3D image editing programs can do this.

    A rendered image can be understood in terms of a number of visiblefeatures. Rendering research and development has been largely motivated byfinding ways to simulate these efficiently. Some relate directly to particular algorithms and techniques, while others are produced together.

    shading how the color and brightness of a surface varies withlighting

    texture-mapping a method of applying detail to surfaces

    http://en.wikipedia.org/wiki/Architectural_renderinghttp://en.wikipedia.org/wiki/Video_gamehttp://en.wikipedia.org/wiki/Simulationhttp://en.wikipedia.org/wiki/Filmhttp://en.wikipedia.org/wiki/Visual_effectshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Visual_systemhttp://en.wikipedia.org/wiki/Mathematicshttp://en.wikipedia.org/wiki/Software_engineeringhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Wireframe_modelhttp://en.wikipedia.org/wiki/Bitmap_textureshttp://en.wikipedia.org/wiki/Procedural_textureshttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Architectural_renderinghttp://en.wikipedia.org/wiki/Video_gamehttp://en.wikipedia.org/wiki/Simulationhttp://en.wikipedia.org/wiki/Filmhttp://en.wikipedia.org/wiki/Visual_effectshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Visual_systemhttp://en.wikipedia.org/wiki/Mathematicshttp://en.wikipedia.org/wiki/Software_engineeringhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Pre-renderedhttp://en.wikipedia.org/wiki/Wireframe_modelhttp://en.wikipedia.org/wiki/Bitmap_textureshttp://en.wikipedia.org/wiki/Procedural_textureshttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Shadinghttp://en.wikipedia.org/wiki/Texture_mapping
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    bump-mapping a method of simulating small-scale bumpiness onsurfaces

    fogging/participating medium how light dims when passingthrough non-clear atmosphere or air

    shadows the effect of obstructing light soft shadows varying darkness caused by partially obscured lightsources

    reflection mirror-like or highly glossy reflection transparency , transparency or opacity sharp transmission of light

    through solid objects translucency highly scattered transmission of light through solid

    objects refraction bending of light associated with transparency diffraction bending, spreading and interference of light passing by

    an object or aperture that disrupts the ray indirect illumination surfaces illuminated by light reflected off

    other surfaces, rather than directly from a light source (also known asglobal illumination)

    caustics (a form of indirect illumination) reflection of light off ashiny object, or focusing of light through a transparent object, to

    produce bright highlights on another object depth of field objects appear blurry or out of focus when too far in

    front of or behind the object in focus

    motion blur objects appear blurry due to high-speed motion, or themotion of the camera non-photorealistic rendering rendering of scenes in an artistic

    style, intended to look like a painting or drawing

    Many rendering algorithms have been researched, and software used for rendering may employ a number of different techniques to obtain a finalimage.

    http://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Distance_foghttp://en.wikipedia.org/wiki/Shadowhttp://en.wikipedia.org/wiki/Soft_shadowshttp://en.wikipedia.org/wiki/Reflection_(computer_graphics)http://en.wikipedia.org/wiki/Transparency_(optics)http://en.wikipedia.org/wiki/Transparency_(graphic)http://en.wikipedia.org/wiki/Opacity_(optics)http://en.wikipedia.org/wiki/Translucencyhttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Global_illuminationhttp://en.wikipedia.org/wiki/Caustic_(optics)http://en.wikipedia.org/wiki/Depth_of_fieldhttp://en.wikipedia.org/wiki/Motion_blurhttp://en.wikipedia.org/wiki/Non-photorealistic_renderinghttp://en.wikipedia.org/wiki/Bump_mappinghttp://en.wikipedia.org/wiki/Distance_foghttp://en.wikipedia.org/wiki/Shadowhttp://en.wikipedia.org/wiki/Soft_shadowshttp://en.wikipedia.org/wiki/Reflection_(computer_graphics)http://en.wikipedia.org/wiki/Transparency_(optics)http://en.wikipedia.org/wiki/Transparency_(graphic)http://en.wikipedia.org/wiki/Opacity_(optics)http://en.wikipedia.org/wiki/Translucencyhttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Global_illuminationhttp://en.wikipedia.org/wiki/Caustic_(optics)http://en.wikipedia.org/wiki/Depth_of_fieldhttp://en.wikipedia.org/wiki/Motion_blurhttp://en.wikipedia.org/wiki/Non-photorealistic_rendering
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    Tracing every ray of light in a scene is impractical and would take anenormous amount of time. Even tracing a portion large enough to producean image takes an inordinate amount of time if the sampling is notintelligently restricted.

    Therefore, four loose families of more-efficient light transport modellingtechniques have emerged: rasterisation , including scanline rendering ,geometrically projects objects in the scene to an image plane, withoutadvanced optical effects; ray casting considers the scene as observed from aspecific point-of-view, calculating the observed image based only ongeometry and very basic optical laws of reflection intensity, and perhapsusing Monte Carlo techniques to reduce artifacts; radiosity uses finite element mathematics to simulate diffuse spreading of light from surfaces;and ray tracing is similar to ray casting, but employs more advanced optical

    simulation, and usually uses Monte Carlo techniques to obtain more realisticresults at a speed that is often orders of magnitude slower.

    Most advanced software combines two or more of the techniques to obtaingood-enough

    Scanl ine re nderi ng and r aste risa tion : -

    A high-level representation of an image necessarily contains elements in adifferent domain from pixels. These elements are referred to as primitives.In a schematic drawing, for instance, line segments and curves might be

    primitives. In a graphical user interface, windows and buttons might be the primitives. In 3D rendering, triangles and polygons in space might be primitives.

    If a pixel-by-pixel approach to rendering is impractical or too slow for sometask, then a primitive-by-primitive approach to rendering may prove useful.Here, one loop through each of the primitives, determines which pixels inthe image it affects, and modifies those pixels accordingly. This is calledrasterization , and is the rendering method used by all current graphics cards .

    http://en.wikipedia.org/wiki/Rasterizationhttp://en.wikipedia.org/wiki/Scanline_renderinghttp://en.wikipedia.org/wiki/Ray_castinghttp://en.wikipedia.org/wiki/Monte_Carlo_methodhttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Ray_tracinghttp://en.wikipedia.org/wiki/Graphics_cardhttp://en.wikipedia.org/wiki/Graphics_cardhttp://en.wikipedia.org/wiki/Rasterizationhttp://en.wikipedia.org/wiki/Scanline_renderinghttp://en.wikipedia.org/wiki/Ray_castinghttp://en.wikipedia.org/wiki/Monte_Carlo_methodhttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Finite_elementhttp://en.wikipedia.org/wiki/Ray_tracinghttp://en.wikipedia.org/wiki/Graphics_cardhttp://en.wikipedia.org/wiki/Graphics_card
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    Rasterization is frequently faster than pixel-by-pixel rendering. First, largeareas of the image may be empty of primitives; rasterization will ignorethese areas, but pixel-by-pixel rendering must pass through them. Second,rasterization can improve cache coherency and reduce redundant work by

    taking advantage of the fact that the pixels occupied by a single primitivetend to be contiguous in the image. For these reasons, rasterization is usuallythe approach of choice when interactive rendering is required; however, the

    pixel-by-pixel approach can often produce higher-quality images and ismore versatile because it does not depend on as many assumptions about theimage as rasterization.

    The older form of rasterization is characterized by rendering an entire face(primitive) as a single color. Alternatively, rasterization can be done in amore complicated manner by first rendering the vertices of a face and then

    rendering the pixels of that face as a blending of the vertex colors. Thisversion of rasterization has overtaken the old method as it allows thegraphics to flow without complicated textures (a rasterized image when usedface by face tends to have a very block-like effect if not covered in complextextures; the faces aren't smooth because there is no gradual color changefrom one primitive to the next). This newer method of rasterization utilizesthe graphics card's more taxing shading functions and still achieves better

    performance because the simpler textures stored in memory use less space.Sometimes designers will use one rasterization method on some faces andthe other method on others based on the angle at which that face meets other

    joined faces, thus increasing speed and not hurting the overall effect.

    Ray casting: -

    Ray casting is primarily used for realtime simulations, such as those used in3D computer games and cartoon animations, where detail is not important,or where it is more efficient to manually fake the details in order to obtain

    better performance in the computational stage. This is usually the case whena large number of frames need to be animated. The resulting surfaces have acharacteristic 'flat' appearance when no additional tricks are used, as if objects in the scene were all painted with matte finish.

    The geometry which has been modeled is parsed pixel by pixel, line by line,from the point of view outward, as if casting rays out from the point of view.

    http://en.wikipedia.org/wiki/Cache_coherencyhttp://en.wikipedia.org/wiki/Interactivityhttp://en.wikipedia.org/wiki/Ray_castinghttp://en.wikipedia.org/wiki/Cache_coherencyhttp://en.wikipedia.org/wiki/Interactivityhttp://en.wikipedia.org/wiki/Ray_casting
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    Where an object is intersected, the color value at the point may be evaluatedusing several methods. In the simplest, the color value of the object at the

    point of intersection becomes the value of that pixel. The color may bedetermined from a texture-map . A more sophisticated method is to modify

    the colour value by an illumination factor, but without calculating therelationship to a simulated light source. To reduce artifacts, a number of raysin slightly different directions may be averaged.

    Rough simulations of optical properties may be additionally employed: asimple calculation of the ray from the object to the point of view is made.Another calculation is made of the angle of incidence of light rays from thelight source(s), and from these as well as the specified intensities of the lightsources, the value of the pixel is calculated. Another simulation usesillumination plotted from a radiosity algorithm, or a combination of these

    two.

    Ra di os it y : -

    Radiosity , also known as Global Illumination, is a method which attempts tosimulate the way in which directly illuminated surfaces act as indirect lightsources that illuminate other surfaces. This produces more realistic shadingand seems to better capture the 'ambience ' of an indoor scene. A classicexample is the way that shadows 'hug' the corners of rooms.

    The optical basis of the simulation is that some diffused light from a given point on a given surface is reflected in a large spectrum of directions andilluminates the area around it.

    The simulation technique may vary in complexity. Many renderings have avery rough estimate of radiosity, simply illuminating an entire scene veryslightly with a factor known as ambiance. However, when advancedradiosity estimation is coupled with a high quality ray tracing algorithim,images may exhibit convincing realism, particularly for indoor scenes.

    In advanced radiosity simulation, recursive, finite-element algorithms'bounce' light back and forth between surfaces in the model, until somerecursion limit is reached. The colouring of one surface in this wayinfluences the colouring of a neighbouring surface, and vice versa. Theresulting values of illumination throughout the model (sometimes including

    http://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Ambient_lighthttp://en.wikipedia.org/wiki/Texture_mappinghttp://en.wikipedia.org/wiki/Radiosityhttp://en.wikipedia.org/wiki/Ambient_light
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    for empty spaces) are stored and used as additional inputs when performingcalculations in a ray-casting or ray-tracing model.

    Due to the iterative/recursive nature of the technique, complex objects are particularly slow to emulate. Prior to the standardization of rapid radiositycalculation, some graphic artists used a technique referred to loosely as false radiosity by darkening areas of texture maps corresponding to corners, jointsand recesses, and applying them via self-illumination or diffuse mapping for scanline rendering. Even now, advanced radiosity calculations may bereserved for calculating the ambiance of the room, from the light reflectingoff walls, floor and celiing, without examining the contribution that complexobjects make to the radiosity -- or complex objects may be replaced in theradiosity calculation with simpler objects of similar size and texture.

    If there is little rearrangement of radiosity objects in the scene, the sameradiosity data may be reused for a number of frames, making radiosity aneffective way to improve on the flatness of ray casting, without seriouslyimpacting the overall rendering time-per-frame.

    Because of this, radiosity has become the leading real-time renderingmethod, and has been used from beginning-to-end to create a large number of well-known recent feature-length animated 3D-cartoon films.

    Ray tr ac in g : -

    http://en.wikipedia.org/wiki/False_radiosityhttp://en.wikipedia.org/wiki/False_radiosityhttp://en.wikipedia.org/wiki/Image:SpiralSphereAndJuliaDetail1.jpghttp://en.wikipedia.org/wiki/False_radiosityhttp://en.wikipedia.org/wiki/False_radiosity
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    Spiral Sphere and Julia, Detail , a computer-generated image created byvisual artist Robert W. McGregor using only POV-Ray 3.6 and its built-inscene description language.

    Ray tracing is an extension of the same technique developed in scanlinerendering and ray casting. Like those, it handles complicated objects well,and the objects may be described mathematically. Unlike scanline andcasting, ray tracing is almost always a Monte Carlo technique, that is one

    based on averaging a number of randomly generated samples from a model.

    In this case, the samples are imaginary rays of light intersecting theviewpoint from the objects in the scene. It is primarily beneficial wherecomplex and accurate rendering of shadows, refraction or reflection are

    issues.

    In a final, production quality rendering of a ray traced work, multiple raysare generally shot for each pixel, and traced not just to the first object of intersection, but rather, through a number of sequential 'bounces', using theknown laws of optics such as "angle of incidence equals angle of reflection"and more advanced laws that deal with refraction and surface roughness.

    Once the ray either encounters a light source, or more probably once a setlimiting number of bounces has been evaluated, then the surface

    illumination at that final point is evaluated using techniques describedabove, and the changes along the way through the various bounces evaluatedto estimate a value observed at the point of view. This is all repeated for each sample, for each pixel.

    In some cases, at each point of intersection, multiple rays may be spawned.

    As a brute-force method, ray tracing has been too slow to consider for real-time, and until recently too slow even to consider for short films of anydegree of quality, although it has been used for special effects sequences,and in advertising, where a short portion of high quality (perhaps even

    photorealistic ) footage is required.

    However, efforts at optimizing to reduce the number of calculations neededin portions of a work where detail is not high or does not depend on raytracing features have led to a realistic possibility of wider use of ray tracing.There is now some hardware accelerated ray tracing equipment, at least in

    http://en.wikipedia.org/wiki/POV-Rayhttp://en.wikipedia.org/wiki/Ray_tracinghttp://en.wikipedia.org/wiki/Photorealismhttp://en.wikipedia.org/wiki/POV-Rayhttp://en.wikipedia.org/wiki/Ray_tracinghttp://en.wikipedia.org/wiki/Photorealism
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    prototype phase, and some game demos which show use of real-timesoftware or hardware ray tracing.

    Optimi sa ti on : -

    Optimizations used by an artist when a scene is being developed

    Due to the large number of calculations, a work in progress is usually onlyrendered in detail appropriate to the portion of the work being developed ata given time, so in the initial stages of modeling, wireframe and ray castingmay be used, even where the target output is ray tracing with radiosity. It isalso common to render only parts of the scene at high detail, and to remove

    objects that are not important to what is currently being developed.

    Common optimizations for real time rendering

    For real-time, it is appropriate to simplify one or more commonapproximations, and tune to the exact parameters of the scenery in question,which is also tuned to the agreed parameters to get the most 'bang for the

    buck'.

    Sampling and filtering

    One problem that any rendering system must deal with, no matter whichapproach it takes, is the sampling problem . Essentially, the rendering

    process tries to depict a continuous function from image space to colors byusing a finite number of pixels. As a consequence of the Nyquist theorem ,the scanning frequency must be twice the dot rate, which is proportional toimage resolution . In simpler terms, this expresses the idea that an imagecannot display details smaller than one pixel.

    If a naive rendering algorithm is used, high frequencies in the imagefunction will cause ugly aliasing to be present in the final image. Aliasingtypically manifests itself as jaggies , or jagged edges on objects where the

    pixel grid is visible. In order to remove aliasing, all rendering algorithms (if they are to produce good-looking images) must filter the image function toremove high frequencies, a process called antialiasing .

    http://en.wikipedia.org/wiki/Continuous_functionhttp://en.wikipedia.org/wiki/Nyquist-Shannon_sampling_theoremhttp://en.wikipedia.org/wiki/Image_resolutionhttp://en.wikipedia.org/wiki/Aliasinghttp://en.wikipedia.org/wiki/Jaggieshttp://en.wikipedia.org/wiki/Antialiasinghttp://en.wikipedia.org/wiki/Continuous_functionhttp://en.wikipedia.org/wiki/Nyquist-Shannon_sampling_theoremhttp://en.wikipedia.org/wiki/Image_resolutionhttp://en.wikipedia.org/wiki/Aliasinghttp://en.wikipedia.org/wiki/Jaggieshttp://en.wikipedia.org/wiki/Antialiasing
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    Academic core

    The implementation of a realistic renderer always has some basic element of physical simulation or emulation some computation which resembles or abstracts a real physical process.

    The term " physically-based " indicates the use of physical models andapproximations that are more general and widely accepted outsiderendering. A particular set of related techniques have gradually becomeestablished in the rendering community.

    The basic concepts are moderately straightforward, but intractable tocalculate; and a single elegant algorithm or approach has been elusive for more general purpose renderers. In order to meet demands of robustness,

    accuracy, and practicality, an implementation will be a complexcombination of different techniques.

    Rendering research is concerned with both the adaptation of scientificmodels and their efficient application.

    The r end eri ng eq uat ion : -

    This is the key academic/theoretical concept in rendering. It serves as themost abstract formal expression of the non-perceptual aspect of rendering.

    All more complete algorithms can be seen as solutions to particular formulations of this equation.

    Meaning: at a particular position and direction, the outgoing light (L o) is thesum of the emitted light (L e) and the reflected light. The reflected light beingthe sum of the incoming light (L i) from all directions, multiplied by thesurface reflection and incoming angle. By connecting outward light toinward light, via an interaction point, this equation stands for the whole'light transport' all the movement of light in a scene.

    The Bidirectional Reflectance Distribution Function

    The Bidirectional Reflectance Distribution Function (BRDF) expresses asimple model of light interaction with a surface as follows:

    Light interaction is often approximated by the even simpler models: diffusereflection and specular reflection, although both can be BRDFs.

    http://en.wikipedia.org/wiki/Bidirectional_Reflectance_Distribution_Functionhttp://en.wikipedia.org/wiki/Bidirectional_Reflectance_Distribution_Function
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    2. ^ http://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDE

    http://en.wikipedia.org/wiki/Rendering_(computer_graphics)#cite_ref-0%23cite_ref-0http://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDEhttp://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDEhttp://en.wikipedia.org/wiki/Rendering_(computer_graphics)#cite_ref-0%23cite_ref-0http://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDEhttp://portal.acm.org/citation.cfm?id=1185817&jmp=abstract&coll=GUIDE&dl=GUIDE