Upcoming Deadlines
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Upcoming Deadlines
Homework #12 – Lighting a Scene in MayaDue Thursday, December 1st (This week)20 points (10 points if late)
Homework #13 – Creating Stereoscopic 3D ImagesDue Thursday, December 8th (Next week)20 points (10 points if late)
For full schedule, visit course website:ArtPhysics123.pbworks.com
Pick up a clicker, find the right channel, and enter Student ID
Homework #12Light the scene created in your previous homework assignment using one, two, and three-point lighting.
Created by Candace Downey
One-point Lighting:Light the scene with a single bright spot light on the left side; this is your key light.
Homework #12
Created by Candace Downey
Two-point Lighting:Add a dim fill light on the right side to soften the shadows created by the key light.
Three-point Lighting:Add a bright rim light behind the letters to accentuate their edges from the dark background.
Homework #12
Created by Candace Downey
Render the three scenes, save each image, and upload them to your blog.
Due by 8am on Thurs., December 1st 20 points (if late, 10)
All Assignments and Extra Credit must be turned in by 5pm on Thursday, December 8th (last day of classes)
Final ExamFinal Exam will have of 10 short essay questions on material covered in lecture.Final exam counts for 50 points.
See course website for copy of last semester’s final exam.
You may bring one page of notes double-sided (or two pages single-sided) to the exam.
Survey QuestionHow much time did last week’s homework
(Building a Scene in Maya) take you to complete?A) Less than an hourB) Between one and two hoursC) Between 2 and 4 hoursD) Over four hoursE) Didn’t finish that assignment
Finding the Highlight
A B C
D: None of these
LampWhere does Albert see the highlight reflected off this metal block?
Albert
Finding the HighlightLamp Albert
C Light rays from point C reach Albert.
Review QuestionMatte surfaces, such as paper and cloth, are typically rendered in computer graphics using which shading model?
A) PhongB) BlinnC) ThongD)LambertE) Mambo
Key + Fill
Key only
Review QuestionD) Lambert
A Lambert surface scatters light diffusely so under directional light it looks equally bright from all angles.
Johann Heinrich Lambert (1728–1777)
Review QuestionWhat is the shape of the
mirrors in these photos?
Concave Mirror
Convex Mirror
A)
B)
OriginalImageMirror
Review QuestionA) Concave Mirror
Review QuestionThe dependence of reflection on angle is called the ______ effect.
Looking straight down into a pool of water we see little reflection of the sky.
Looking at the water at a large angle we see a strong reflection of the sky.
Review Question
Small angleLarge angle
Weak Reflection
Strong Reflection
The dependence of reflection on angle is called the ______ effect.
A) Reflex B) Reflux C) RephaseD) Fresnel E) What-The-Flux
Fresnel EffectThe dependence of reflection on angle is called the Fresnel effect.
Looking straight down into a pool of water we see little reflection of the sky.
Looking at the water at a large angle we see a strong reflection of the sky.
Optics & LightingPart III:
Bending & Scattering
Global Illumination
Notice focusing of light through glass sphere
Without GI With GI
Advanced computer graphics uses global illumination algorithms to compute a more physically realistic rendering of a scene.
RefractionLight rays bend (refract) passing from
water to air, making objects appear to be shallower and closer to the observer.
Image
Actual
Image
Actual
Observer sees image
Reciprocity
Laser
Light bends the same way whether it’s entering the water or coming out of the water.
This symmetry for light rays is called “reciprocity.”
Law of Refraction
Light passing from one material to another is refracted by an angle that depends on the optical density of each material.
Angle is smaller in the denser material.
Demo: Refraction thru a Block
Light is refracted entering the block and refracted back on leaving the block.
Optical DensityAir
Water
Air
Glass
Air
Diamond
n = 1.3n = 1.0
n = 1.5n = 1.0
n = 2.4n = 1.0
Optical density is given by the index of refraction, n.
The larger the difference between the indices at an interface, the larger the angle of refraction for light rays crossing the interface.
Demo: InvisibilityMineral oil and
glass have nearly the same index of refraction
A glass rod is nearly invisible in a beaker of mineral oil.
A diamond, however, is easily seen.
Refraction in a WedgeWhich path does
light ray take after entering the glass wedge?
A)Path AB)Path BC)Path C
A
B
C
WEDGE
Path BThe angle always
bends towards the perpendicular going from air to glass.
Notice that it bends away from the perpendicular going back out of the glass.
A
B
C
WEDGE
Refraction in a Wedge
Lenses
Concave lens shrinks its image
Convex lens magnifies its image
Curvature of a lens surface produces a continuous, variable angular refraction.
Demo: Concave LensesCurved surface of a concave lens causes light rays to diverge, dispersing the light and shrinking any images.
Demo: Convex LensesCurved surface of a convex lens
causes light rays to converge, focusing the light and possibly magnifying images.
Camera LensUsing a lens allows for light to be
focused on a screen or camera film.
No image (Diffuse) Camera with lens
Demo: Real Image of Convex LensImage formed by convex lens can be
observed on a screen.
Bokeh Effect (Lens Blur)Point lights expand into balls of light when the light source is out of focus (outside the depth of field).
The term is from the Japanese word boke ( 暈け or ボケ ), which means "blur" or "haze."
Focusing and Shadows
Bright
Dark
When refraction focuses light to create bright areas, it also removes light and creates shadowed areas.
CausticsCaustics are the bright concentrations of light caused by the focusing of that light by refraction or by reflection.
Caustics also create shadow patterns, which visually accent the caustic’s brightness.
Refraction caustics
Reflection caustics
Total Internal ReflectionWhen refraction angle exceeds 90º the
light does not cross the surface.
Refracted
ReflectedReflected
Demo: Total Internal Reflection
Just below critical angle
Past the critical angle all the light is internally reflected.
Demo: Total Internal ReflectionPrism demonstrates total internal reflection if the angle of incidence is large enough.
No light escapes to this side
No light escapes to this side
No light escapes to this side
Looking up UnderwaterTry this when you’re in the pool
or the ocean next summer.
Looking straight up you see the sky but outside the 96° cone surface is like a mirror
Natural Lighting UnderwaterDue to total internal refraction sunlight never enters the water at more than about a 45 degree angle.
Image seen underwater
Sun
Fiber OpticsTotal internal reflection causes light to reflect inside a solid glass tube.
Separating ColorsBlue wavelength of light refracts
slightly more than the red, creating rainbows.
Glass Prism
WaterDroplet
RainbowsRainbows are formed by refraction
from many, many raindrops. The red part is always above the blue part.
Double Rainbow
Primary
Secondary
Atmospheric PerspectiveObjects in the distance have a bluish,
unsaturated color due to atmospheric scattering of blue light (same as blue sky).
Atmospheric Perspective Example
Mt. Hadley
View From EVA 3
Apollo 15 Landing SiteMt. Hadley
(14,000 ft)
Photographer
20 km
Mt. Hadley Delta
(11,000 ft)
Mauna Loa (~height as Mt. Hadley) from ~20 km away
“Perspective of Color”Not only did he make good use of
what he called “Perspective of Color” but Leonardo also correctly predicted that this is why the sky is blue.
The Virgin of the Rocks, Leonardo, 1482
Light ScatteringMie ScatteringScattering by particles, such as droplets of fog, of micron size.
Also called Rayleigh-Brillouin Scattering*
Rayleigh Scattering*Refraction by random variations in a transparent medium.
For both types of scattering blue light tends to scatter more strongly than red light.
Mie Scattering
Notice the shadows
Particles in Mie scattering are often transparent or highly reflective.
Suspended ParticlesA dust storm is seen from the reflection off the suspended dust particles rather than true scattering.
Mie scattering by water droplets in clouds.
Reflection from suspended particles.
Rayleigh ScatteringSky is blue due to Rayleigh scattering of sunlight in the atmosphere.
When sunlight passes through a very thick layer all the blue is scattered out and we’re left with yellowish red.
Underwater PerspectiveWater is transparent but absorbs red light about x100 more than blue light.
Objects in distance are bluish but saturated.
Significant reflection by suspended particles.
Particles are easily mixed in water due to buoyancy.
Volumetric LightingVolumetric lighting is used to create the volume of scattered light, usually due to Mie scattering.
Call of Duty: Black Ops (2010)
http://www.youtube.com/watch?v=l7PRTYn3ZMk
Atmospheric effects are important for creating the right look for this snow level in the game.
Next LectureSeeing Color
HW #12 Due Thursday
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