introduction to 3d graphics lecture 1: illusions and the fine art of approximation anthony steed...
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Introduction to 3D GraphicsIntroduction to 3D Graphics
Lecture 1: Illusions and the Lecture 1: Illusions and the Fine Art of ApproximationFine Art of Approximation
Anthony SteedAnthony Steed
University College LondonUniversity College London
OutlineOutline
About the CourseAbout the Course Anatomy of an IllusionAnatomy of an Illusion
– EnvironmentEnvironment– Light transport and interactionLight transport and interaction– Reception at the eyeReception at the eye
The Painter’s Method The Painter’s Method – Ray-castingRay-casting– ApproximationsApproximations
OutlineOutline
About the CourseAbout the Course Anatomy of an IllusionAnatomy of an Illusion
– EnvironmentEnvironment– Light transport and interactionLight transport and interaction– Reception at the eyeReception at the eye
The Painter’s Method The Painter’s Method – Ray-castingRay-casting– ApproximationsApproximations
EnvironmentEnvironment
A description of a space consisting of A description of a space consisting of objectsobjects
Objects have Objects have description description and and statestate Description consists of Description consists of behaviourbehaviour, ,
geometry geometry and and appearanceappearance Geometry must be described relative to Geometry must be described relative to
a a co-ordinate frameco-ordinate frame State defines the object at a particular State defines the object at a particular
moment in timemoment in time
Radiometry - Radiometry - How does light How does light propagate in the real world?propagate in the real world?
700nm 400nm
pure light
spectral distribution
white light
Life and Death of a PhotonLife and Death of a Photon
EmissionEmission
ReflectionReflection
AbsorptionAbsorption
Lighting is a Global Lighting is a Global ProblemProblem
That is, if you consider any point in That is, if you consider any point in the environment, it receives light the environment, it receives light from all aroundfrom all around
Surfaces are Rarely Surfaces are Rarely MirrorsMirrors
Specular surfaceSpecular surface
Diffuse SurfaceDiffuse Surface
Some Simplifying Some Simplifying AssumptionsAssumptions
Wavelength independenceWavelength independence– No fluorescenceNo fluorescence
Time invarianceTime invariance– No phosphorescenceNo phosphorescence
Light transport in a vacuumLight transport in a vacuum– No participating mediaNo participating media
Objects are isotropicObjects are isotropic– Reflectance characteristics are Reflectance characteristics are
constant over the surfaceconstant over the surface
Photometry - Photometry - How do we see How do we see light?light?
Physiology of Eye Physiology of Eye ResponseResponse
6 million cones in the fovea6 million cones in the fovea– cones sense red green or blue lightcones sense red green or blue light– colour perception region is very smallcolour perception region is very small
120 million rods over the whole 120 million rods over the whole eyeeye– peripheral visionperipheral vision– motion sensitivemotion sensitive
Colour ResponseColour Response
ConesCones A = “Red”A = “Red” B = “Green”B = “Green” C = “Blue”C = “Blue”
Assumption for Real-Time Assumption for Real-Time GraphicsGraphics
Ignore “real” spectral distributionsIgnore “real” spectral distributions Instead calculate at three Instead calculate at three
wavelengths, Red, Green and Blue wavelengths, Red, Green and Blue that monitors providethat monitors provide
Obviously this is a gross Obviously this is a gross approximationapproximation– Really should find the spectrum for each Really should find the spectrum for each
point calculate the closest RGB valuepoint calculate the closest RGB value
RGB Colour ModelRGB Colour Model
WHITE
MAGENTA (1,0,1)RED (1,0,0)
BLACK
GREEN (0,1,0) CYAN (0,1,1)
BLUE (0,0,1)
YELLOW (1,1,0)
Colour MatchingColour Matching
How much R,G,B do you need to make a particular “pure” colour?
OutlineOutline
About the CourseAbout the Course Anatomy of an IllusionAnatomy of an Illusion
– EnvironmentEnvironment– Light transport and interactionLight transport and interaction– Reception at the eyeReception at the eye
The Painter’s Method The Painter’s Method – Ray-castingRay-casting– ApproximationsApproximations
Painting Through a Painting Through a WindowWindow
COPView Window (showing pixels)
COP = Centre of Projection
Major Concepts of Major Concepts of GraphicsGraphics
Separation of Scene Specification, Viewing and Rendering
– Scene is modelled independent of any view
– Views are unconstrained
– There are many possible rendering methods given a scene and a view
Major Concepts of Major Concepts of GraphicsGraphics
View volume
– The extent of the pixels on the screen and the COP define a pyramid
– Clipping is the process of removing anything from the scene that is not the view volume
Major Concepts of Major Concepts of GraphicsGraphics
Aliasing Aliasing – Pixels are square and only Pixels are square and only sample sample the the
actual lightactual light
Combating AliasingCombating Aliasing
Send several rays through each pixelSend several rays through each pixel– Stochastic sampleStochastic sample– Regular sample (full-screen anti-aliasing)Regular sample (full-screen anti-aliasing)
Stochastic sample is “correct” since it Stochastic sample is “correct” since it removes regularityremoves regularity
But only regular sample is easy with But only regular sample is easy with the rendering pipelinethe rendering pipeline
Major Concepts of Major Concepts of GraphicsGraphics
Perspective ProjectionPerspective Projection– Image size depends on distanceImage size depends on distance
COP
Major Concepts of Major Concepts of GraphicsGraphics
LightingLighting– Ray-casting is the simple partRay-casting is the simple part– Determining the colour of the pixel is Determining the colour of the pixel is
hard for all the reasons described hard for all the reasons described earlierearlier
– Theoretically we have to calculate all Theoretically we have to calculate all incoming lightincoming light
– In practice we will consider only In practice we will consider only local local illuminationillumination - light received directly - light received directly from light sourcesfrom light sources
SummarySummary
Taken a brief look at the general Taken a brief look at the general problem of doing visual simulationproblem of doing visual simulation
Reviewed the limits of human responseReviewed the limits of human response Given an over-view of the simulation Given an over-view of the simulation
process and the concepts ofprocess and the concepts of– Scene, view, renderingScene, view, rendering– AliasingAliasing– ProjectionProjection– LightingLighting
Future WorkFuture Work
To DevelopTo Develop– Mathematics of scene descriptionMathematics of scene description– Geometric descriptionsGeometric descriptions– Lighting modelsLighting models– Move from ray-cast to forward Move from ray-cast to forward
projectionprojection Stages in the graphics pipelineStages in the graphics pipeline