Upcoming Deadlines
Second Term Paper
Wednesday, November 25th
(This Wednesday; no class that day)
Homework 11 (Building a scene in Maya)
Monday, November 30th (Monday after Thanksgiving)
Homework 12 (Lighting a scene in Maya)
Monday, December 7th (Last day of class)
For full schedule, visit course website:
ArtPhysics123.pbworks.com
Homework Assignment
Using Autodesk Maya create a scene consisting
of a floor, a single wall in the background, and
some objects in the foreground in the form of
the initials of your name.
Render the scene, save
the image, and upload it
to your blog.
Due by 8am on Monday,
November 30th.
20 points (if late, 10)
Created by Candace Downey
Final Exam
Final Exam will have of 10 short essay
questions on material covered in lecture.
Final exam counts for 50 points.
Sample Questions:
* What is the difference between stride and
gait? How do they affect the walking speed?
* Describe how a scene would be lit using three
point lighting.
Final Exam
Final exam is scheduled for:
Wednesday, December 16th
In this room from 1215—1430
You may take the final early on:
Wednesday, December 9th
In this room from 1500—1700
Special Campus Event
Animation Show of Shows
December 7th
(Monday)
At 7:30 PM
Morris Dailey
Auditorium
in Tower Hall
FREE
Optics & Lighting
Part II:
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
Caustics
Caustics are the bright
concentrations of light
caused by the focusing
of that light when
passing through a
transparent object.
Caustics also create shadow
patterns, such as the bright and
dark pattern in a swimming pool,
due to the deflection of the light.
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
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
Mirages
Mirages are caused
by the refraction of
air because hot air
has lower optical
density than cold air.
Cool Air
Hot Air
Total Internal Reflection
When refraction angle exceeds 90º the
light does not cross the surface.
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.
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.
Demo: Real Image of Convex
Lens
Image formed by convex lens can be
observed on a screen.
Pinhole Camera
Small pinhole allows only small amount
of light in, blocking overlapping
diffuse rays and forming image inside
the camera.
Demo: Pinhole Lens
Make a small pinhole in a piece of
cardboard. You’ll find that you can focus
better when looking through the pinhole.
E
TG
WRP
This works best if you
remove any corrective
lenses, such as contacts
and eyeglasses.
OCVM
XSRYU
QBNEHD
Camera Obscura
The camera obscura (room darkened) dates to ancient times;
it was first detailed in the writings of Leonardo da Vinci.
A room is completely sealed from light except for a coinsized hole in one wall. An image of the outside world
appears projected, upside down and reversed right-toleft, onto a wall opposite the opening.
Diffuse light
Giant Camera
Camera obscura with a projecting mirror.
Mirror
Next to the Cliff House, San Francisco
Mirror
Johannes Vermeer (1632-75)
Common elements in his paintings and ray tracing
analysis suggest that this great Dutch artist
may have built a camera obscura in his studio.
The Music Lesson
Vermeer
Camera Lens
Using a lens allows for more light to be
focused on the camera screen or film.
No image (Diffuse)
Camera obscura
Camera with lens
The Lens of the Eye
The eye’s lens changes shape to focus the
image onto light sensitive cells of retina.
Image is formed upside-down
on the retina of the eye.
Visual Acuity
If eye’s lens is unable to form image on
the retina, an object will appear out
of focus.
Myopia
Hyperopic
Eyeglasses
Lenses of eyeglasses
restore visual acuity by
combining with the eye’s
lens to form focused
image onto retina.
Eyeglasses began to appear
in common use in the 13th
century. They may have
been invented in northern
Italy but Marco Polo
reports them in China as
early as 1275.
Detail of portrait of Hugh de
Provence, Tomasso da Modena, 1352
Pinhole glasses
Astigmatism
Astigmatism due to eye’s lens being elliptical,
which causes the focus in the vertical to
differ from horizontal.
Vertical focus
Astigmatism may be corrected
using a cylindrical lens.
In this example, the lens
focuses in the horizontal only
since vertical is already in focus.
Spectrum of Visible Light
Demo: Infrared Light
Digital cameras, such as in cell phones, are
sensitive to infrared light, such as from
a remote control or any hot object.
Microwave
Transmitter
Microwave
Receiver
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
Diamond Cuts
Diamonds are cut so as to create a
beautiful jewelry by taking advantage of
total internal reflection and high color
dispersion (prism effect).
Atmospheric Perspective
Objects in the distance have a bluish,
unsaturated color due to atmospheric
scattering of blue light (same as blue sky).
Atmospheric Perspective Example
“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
Direct scattering by
suspended particles,
such as dust, fog, etc.
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 Examples
Volumetric Lighting
Volumetric lighting is used
to create the volume of
scattered light, usually due
to Mie scattering.
Next Lecture
Seeing Color
No class this Wednesday but
Second Term Paper due on Wednesday
Please return the clickers!