Lights and LightingLights and Lighting
Digital Lighting and RenderingCGT 340CGT 340
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Lighting is 5% of light setup and 95% of i i d djrevisions and adjustments.
Jeremy Birn
Bedrich Benes, [email protected]
Jeremy Birn
Lecture overviewLecture overview
What is light?What is light?SpectrumT i lTypical casesMetamersCG lights
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LightLight
Light electromagnetic radiationLight electromagnetic radiation between ~ 400 nm and ~ 700 nm
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Light SourcesLight Sources
Light sourceLight sourcecan be characterized by its
emission spectrum oremission spectrum or spectral characteristicgraph of intensity of emission at differentgraph of intensity of emission at different wavelengths
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Light SourcesLight Sources
the daylight emission spectrumthe daylight emission spectrumit can be measured
intensity [W]
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400 500 600 700 wavelength [nm]
Light SourcesLight SourcesLight sourcegimportant special cases of light sources
intensity[W]
intensity [W] [W]
400 500 600 700 wavelength [nm] 400 500 600 700
wavelength [nm]
achromatic light monochromatic lightlat. chroma = color
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Light SourcesLight Sources
achromaticachromaticis usually perceived as white or gray
increasing/decreasing the intensity of theg g yachromatic light we get brighter/darker gray
monochromatic (includes one chroma) is usually perceived as a pure color
the only intensity is the d i t l th d i t fdominant wavelength or dominant frequencyexamples are a laser beam, a sodium bulb
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Light Sources and ColorLight Sources and Color
Will two different spectra be perceivedWill two different spectra be perceived as two different colors?
Always?
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MetamersMetamers
Two lights with different spectra that areTwo lights with different spectra that are perceived as the same color are called metamersmetamers.
Wh ?Why?Convolution of the emission spectra over the eye light sensitivity for short, medium, and long cones gives the same numbers.
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Color matching experimentColor matching experiment
change intensity Lchange intensity of the three lightsget the same color
LMSget the same color
as of the sourcel t th th li htlet the three lights be called A, B, and Cthey are called primaries
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Light in Computer GraphicsLight in Computer Graphics
the three componentsthe three components
Diff li htDiffuse light
SSpecular light
Ambient light
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Light in Computer GraphicsLight in Computer Graphics
Diffuse ~ colorDiffuse colorSpecular ~ reflections, highlightsA bi t i di t ill i tiAmbient ~ indirect illumination,
multiple reflections
This comes from reflections and it characterizes the material more than lights
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Types of light sourcesTypes of light sources
Based on the way they shine:Based on the way they shine:Ambient lightPoint lightPoint lightSpot lightDirectional lightgArea lightVolume light
Let’s meet them personally
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p y
Ambient LightAmbient Light
Why not to use it?Why not to use it?does not depend on any angleis a flattered fill of a coloris a flattered fill of a colorthe best is – turn it OFFbut we do need the indirect illuminationbut we do need the indirect illumination…use fill lights, but dim them
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Ambient Light – one lightAmbient Light one light
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Ambient Light - ambientAmbient Light ambient
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Ambient Light - directionalAmbient Light directional
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Ambient [0 0 25 0 5 1 0]Ambient [0, 0.25, 0.5, 1.0]
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Ambient LightAmbient Light
MayaMayaAttribute Ambient Shade=0 > behaves as ambientAmbient Shade=0 -> behaves as ambientAmbient Shade=1 -> behaves as point
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Point Light SourcePoint Light Source
Also called omni omnidirectionalAlso called omni, omnidirectionalDoes not exist in realityM th ti l b t tiMathematical abstractionLike a light bulb in the middle of a roomThe fastest light source to calculate
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Point Light SourcePoint Light Source
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Point Light SourcePoint Light Source
Trick in MayaTrick in Mayaset negative intensityintensitybehaves like a “negative light”negative light
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Spot LightSpot Light
The most commonly usedThe most commonly usedProbably the most powerful light sourceTh b t t ll d li htThe best controlled lightIt is a point light that is aimed somewhereIt has its:target, cone, penumbra angle, etc.g , , p g ,
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Spot LightSpot Light
ReflectorReflectorPoint light with more parametersmore parametersPositioning
press object pick (“T”) to put and situate
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Spot Light - positioningSpot Light positioning
Select lightSelect lightPanel-> Look through selected
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Spot Light - positioningSpot Light positioning
Aiming to an objectAiming to an objectPanel -> View -> Look at Selection
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Spot Light- cone angle 40oSpot Light cone angle 40
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Spot Light- cone angle 70oSpot Light cone angle 70
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Spot Light- penumbra angle 20oSpot Light penumbra angle 20
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Spot Light- drop-off 140Spot Light drop off 140
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Spot Light – color as a fileSpot Light color as a file
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Spot Light – color as a fileSpot Light color as a file
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ThrowThrow
Cookies and gobosCookies and gobos“cookie” – cucoloris“ b ” b t“gobo” – go-betweenobjects between lights and the occluderVenetian blinds, fan on ceiling etc.Can be done by a modelyEasier by a light map
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ThrowThrow
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Spot – light mapping intensitySpot light mapping intensity
I=f(d)I f(d)Can be mapped manuallyThe Graph EditorThe Graph EditorWindow -> Animation Editors -> Graph editorAnimation Editors Graph editorSelect the spotlightIn the Light Effect option select Intensity CurvesIn the Light Effect option select Intensity CurvesUse the middle key to move the points
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Spot – light mapping intensitySpot light mapping intensity
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Spot – light mapping intensitySpot light mapping intensity
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Spot Light – making a soft shadowSpot Light making a soft shadow
DLR 2nd edition page 22DLR 2 edition page 22Aim multiple lights so they overlapD th b lDecrease the penumbra angle It is not a shadow! But it looks cool…
Bedrich Benes, [email protected]© Digital Lighting and rendering 2nd edition J.Birn
Directional LightDirectional Light
Depends only on an angleDepends only on an angle Translation does not make any senseRepresents distantRepresents distant light sourcesPoint in infinity (vector)Point in infinity (vector)All rays are parallelF t t l l tFast to calculateCan project images
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Directional LightDirectional Light
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Area LightArea Light
spherical lightspherical lightgood when close to an objectfor large distance ~ pointg pflat areadisc, rectanglegfaster to calculategood for lamps, etclinear lightfluorescent tube
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Area LightArea Light
Rectangular (in Maya)Rectangular (in Maya)The slowest to calculateTh l th t d ft h dThe only that produces soft shadowsObject pick (“T”) to put and situate
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Area LightArea Light
The size does matter!The size does matter!
Th bi th li htThe bigger the light source, the more illuminated the scene
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Area LightArea Light
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Volume LightVolume Light
In MayaIn Maya3D shape and the light direction (in out etc )the light direction (in, out, etc.)Everything inside the volume i ill i t dis illuminated
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Volume LightVolume Light
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Light LinkingLight Linking
Also called selective lightingAlso called selective lightingMaya – Relationship EditorLi ht/Sh di Li ht li kiLight/Shading -> Light linkingDefines which light shines on which objectCan significantly increase
speed of renderingp g
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Light Linking – two lightsLight Linking two lights
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Light LinkingLight Linking
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Light LinkingLight Linking
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ShadowsShadows
one of the most important visual cluesone of the most important visual clueshelp to establish spatial relationship
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ShadowsShadows
can help to see alternate anglescan help to see alternate angles
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ShadowsShadows
increase contrast of a sceneincrease contrast of a sceneshadow color is important!intense color can be usedintense color can be used to see what is actually lit
can help to divide the space
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ShadowsShadows
Black shadow is not natural (always?)Black shadow is not natural (always?)
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ShadowsShadows
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ShadowsShadows
Use fill light to brighten shadowsUse fill light to brighten shadows
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Shadows - algorithmsShadows algorithms
Shadow mapShadow mapfast and usually uglyproblems with transparencyproblems with transparency
Raytraced shadowsexcellent choiceslowcritical – shadow rayshigher ~ slower, better
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Shadow GeometryShadow GeometryLight source
Occluder
UmbraReceiver Penumbra Penumbra
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Can a point light produce soft shadows?
Shadows - raytracedShadows raytraced
Penumbra quality = f(shadow rays)Penumbra quality = f(shadow rays)
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Shadows – shadow mappedShadows shadow mapped
Shadow quality = f(size of the map)Shadow quality = f(size of the map)
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Ambient OcclusionAmbient Occlusion
important and neat effect that darkensimportant and neat effect that darkens wrinkled partsdone by hemicube or hemisphericaldone by hemicube or hemispherical sampling
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Ambient OcclusionAmbient Occlusion
Can be achieved by Global IlluminationCan be achieved by Global Illumination
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Ambient OcclusionAmbient Occlusion
is calculated without a light sourceis calculated without a light sourcevery soft shadows
ivery nice
details – laterin Global Illumination
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Lens Flares and HalosLens Flares and Halos
Nice and cheap effectNice and cheap effectCaused by multiple reflectionsin camera’s lensesin camera s lensesIn Maya associated with a light sourceCan be active/inactive
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Lens Flares and HaloesLens Flares and Haloes
Select light sourceSelect light sourceGo to Light effects and select Light Glowand select Light GlowSelect Lens FlaresGlow spread controlsGlow spread controlsthe distance the glowgoesgoesIgnore light will display just the effect
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just the effect
Lens Flares and HaloesLens Flares and Haloes
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Qualities of lightQualities of light
Soft/HardSoft/HardIntensityC lColorThrowAnimation
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Soft/Hard LightSoft/Hard Light
Means in fact soft/hard shadowMeans in fact, soft/hard shadowSoft shadows can be simulated by more light sourcescan be simulated by more light sources
fasters, easierh li ht ill h 1/ th i t iteach light will have 1/n-th intensity
Hard light – sunlight, close light bulb
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Soft/Hard LightSoft/Hard Light
Hard lightHard light sunlight, close light bulbspace scenes inhospitable environmentsspace scenes, inhospitable environments
S ft li htSoft lightswarm environmentsdi t li htdistance lights
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Rules of thumbRules of thumb
Isolate one light to see its influenceIsolate one light to see its influenceStart with small intensitiesLi hti i li ! (th G d!)Lighting is linear! (thanx G-d!)Use flipbook to see the influencesArea lights at the endArea lights may notArea lights may not be necessary in animations
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To take homeTo take home…
Light isLight is…MetamersT f li ht ( i t t )Types of light sources (point, spot…)Why not to use ambient lightWhy a spot is the best light sourceShadows and tricks with themShadows and tricks with themRules of thumb
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ReadingsReadings- Andrew Glassner, Principles of Digital Image Synthesisp g g y- Donald Hearn, M.Pauline Baker.
Computer Graphics, 2nd edition, Prentice Hall 1994F S Hill- F.S.Hill,
Computer Graphics, Prentice Hall 1990, pages 564->- Watt, Watt, 2nd edition,
Ad d A i ti d R d i T h iAdvanced Animation and Rendering Techniques- Cohen, Wallace,
Radiosity and Realistic Image Synthesisy y
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