Transcript of refraction - artphysics123

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Homework #12 – Lighting a Scene in Maya
Due Wednesday, December 1st (Week from today)
20 points (10 points if late)
Homework #13 – Creating Stereoscopic 3D Images
Due Wednesday, December 8th (In two weeks)
20 points (10 points if late)
For full schedule, visit course website:
ArtPhysics123.pbworks.com
Homework #12
Light the scene created in your previous
homework assignment using one, two, and
three-point lighting.
One-point Lighting:
Light the scene with a
single bright spot light on
the left side; this is your
key light.
Created by Candace Downey
Homework #12
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
Created by Candace Downey
from the dark background.
Homework #12
Render the three scenes, save each
image, and upload them to your blog.
Due by 8am on Wed., December 1st
20 points (if late, 10)
All Assignments and Extra Credit must
be turned in by 5pm on Tuesday,
Candaceexam)
Downey
December 14th (day of Created
the byfinal
Final Exam
Final 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 doublesided (or two pages single-sided) to the
exam.
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Survey Question
How much time did this week’s homework
(Building a Scene in Maya) take you to
complete?
A)
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Less than an hour
Between one and two hours
Between 2 and 4 hours
Over four hours
Didn’t finish that assignment
Finding the Highlight
Lamp
Where does Albert
see the highlight
reflected off this
metal block?
A
B
D: None of these
C
Albert
Finding the Highlight
Lamp
Albert
C
Light rays
from point C
reach Albert.
Review Question
Matte surfaces, such as paper
and cloth, are typically
rendered in computer graphics
using which shading model?
A) Phong
B) Blinn
C) Thong
D) Lambert
E) Mambo
Key only
Key + Fill
Review Question
D) Lambert
Johann Heinrich
Lambert (1728–1777)
A Lambert surface scatters light diffusely so under
directional light it looks equally bright from all angles.
Review Question
What is the shape of the
mirrors in these photos?
A)
B)
Concave Mirror
Convex Mirror
Review Question
A) Concave Mirror
Original
Mirror
Image
Review Question
The 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
The dependence of reflection on angle
is called the ______ effect.
A) Reflex
D) Fresnel
Small angle
B) Reflux
C) Rephase
E) What-The-Flux
Large angle
Weak
Reflection
Strong
Reflection
Fresnel Effect
The 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 & Lighting
Part III:
Bending &
Scattering
Global Illumination
Advanced computer graphics uses global
illumination algorithms to compute a more
physically realistic rendering of a scene.
Without GI
With GI
Notice focusing of light through glass sphere
Refraction
Light rays bend (refract) passing from water
to air, making objects appear to be
shallower and closer to the observer.
Observer sees image
Image
Image
Actual
Actual
Reciprocity
Light bends the same way whether it’s entering
the water or coming out of the water.
Laser
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 Density
Optical density is
given by the index of
refraction, n.
Air
The larger the
difference between
the indices at an
interface, the larger
the angle of
refraction for light
rays crossing the
interface.
Air
Water
Glass
Air
Diamond
n = 1.0
n = 1.3
n = 1.0
n = 1.5
n = 1.0
n = 2.4
Demo: Invisibility
Mineral 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 Wedge
Which path does
light ray take
after entering
the glass wedge?
A)Path A
B) Path B
C) Path C
A
B
C
WEDGE
Refraction in a Wedge
Path B
The 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
Lenses
Curvature of a lens surface produces a
continuous, variable angular refraction.
Concave lens
shrinks its
image
Convex lens
magnifies its
image
Demo: Concave Lenses
Curved surface of a concave lens
causes light rays to diverge, dispersing
the light and shrinking any images.
Demo: Convex Lenses
Curved surface of a convex lens causes
light rays to converge, focusing the
light and possibly magnifying images.
Camera Lens
Using 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 Lens
Image 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
When refraction
focuses light to create
bright areas, it also
removes light and
creates shadowed areas.
Dark
Bright
Caustics
Refraction caustics
Caustics are the bright
concentrations of light
caused by the focusing of
that light by refraction or
Reflection caustics
by reflection.
Caustics also create shadow
patterns, which visually accent
the caustic’s brightness.
Total Internal Reflection
When refraction angle exceeds 90º the
light does not cross the surface.
Atmospheric Perspective Example
Demo: Total Internal Reflection
Past the critical
angle all the light is
internally reflected.
Just below critical angle
Demo: Total Internal Reflection
Prism 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 Underwater
Try 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 Underwater
Due to total internal refraction sunlight
never enters the water at more than
about a 45 degree angle.
Image seen
underwater
Sun
Fiber Optics
Total internal reflection
causes light to reflect
inside a solid glass tube.
Separating Colors
Blue wavelength of light refracts slightly
more than the red, creating rainbows.
Water
Droplet
Glass Prism
Rainbows
Rainbows are formed by refraction
from many, many raindrops. The red
part is always above the blue part.
Double Rainbow
Primary
Secondary
Atmospheric Perspective
Objects in the distance have a bluish,
unsaturated color due to atmospheric
scattering of blue light (same as blue sky).
“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 Scattering
Mie Scattering
Scattering by particles,
such as droplets of fog,
of micron size.
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.
Also called Rayleigh-Brillouin Scattering*
Mie Scattering
Notice the
shadows
Particles in Mie
scattering are often
transparent or
highly reflective.
Suspended Particles
A 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 Scattering
Sky 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 Perspective
Water 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 Lighting
Volumetric lighting is used
to create the volume of
scattered light, usually due
to Mie scattering.
Call of Duty: Black Ops (2010)
Atmospheric effects are important for creating
the right look for this snow level in the game.
http://www.youtube.com/watch?v=l7PRTYn3ZMk
Next Lecture
Seeing Color
Happy Thanksgiving
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