Transcript of refraction - artphysics123

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Homework #12 –Cameras and Lights in Maya
Due Tuesday, May 8th (Next week)
20 points (10 points if late)
Homework #13 – Creating Stereoscopic 3D Images
Due Tuesday, May 15th (Last day of classes)
20 points (10 points if late)
For full schedule, visit course website:
ArtPhysics123.pbworks.com
Homework #12
For this assignment you are given a photograph
of a real object and you will try to match the
camera and the lighting.
Each person will have a choice of four photos; for
the assignment match any one of these photos
(for extra credit, do more than one).
To find the photographs assigned to you, go to:
http://tinyurl.com/6uom7kp
Photo
Homework #12
The Maya model for this "widget" object has been
created for you and may be downloaded here:
http://tinyurl.com/7zhsaf7
Open the object in Maya, create a surface for it to sit on,
position the camera, add some lights, and adjust
everything until your rendered Maya image looks as
closely as possible to the photograph.
Try to match any colors, for the object and the lights, as
well as the details of the shadows (e.g., penumbra
angles, ambient light, drop-off).
Maya Render
Homework #12
To finish, move the position of your camera to view
the scene from another direction (suggest that you
turn the camera roughly 45 degrees to either side).
Render #1
Render #2
Homework #12
Finally, upload the photo you chose to use and the
two Maya rendered images into a posting entitled
"Recreating Cameras and Lights in Maya."
Note that this is a new assignment this year so
there are no examples from previous semesters;
contact me if you have any questions.
Due by 8am on Tuesday, May 8th
20 points (10 points if late)
Homework #12
Non-Maya Alternative: One of the four photographs is a pair of
soup cans. Recreate the camera and lighting in that photograph
as accurately as possible then take your own photos of the
scene.
Finish by taking a second photograph with the camera at about
45 degrees to either side of its original position.
Upload both of your photographs as well as the photograph that
you're matching.
Note that it will not be easy to duplicate the lighting conditions
using common house lamps; only do this alternative if you find it
absolutely impossible to work with Maya.
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 an example
of a final exam from an earlier semester.
You may bring one page of notes doublesided (or two pages single-sided) to the
exam.
Final Exam
Final exam is on Tuesday, May 22nd from
1215 to 1430 in this classroom.
Visit the course website for more info on
your final exam (including sample).
Note that the final exam is optional.
All Assignments and Extra Credit must be
turned in by 5pm on May 22nd
Survey Question
How would you describe your
experience using AutoDesk Maya?
A)
B)
C)
D)
E)
It’s a lot of fun to use
Difficult to use but worth it
Don’t like Maya all that much
It’s a living Hell
Haven’t used Maya
Review Question
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
Lambert Reflection
D) Lambert
Lamp
Lambert surface
looks equally
bright under
different viewing
angles.
Review Question
The dependence of reflection on
angle is called the ______ effect.
A) Reflex
D) Fresnel
B) Reflux
C) Doppler
E) What-The-Flux
Large angle
Small angle
Weak
Reflection
Strong
Reflection
Fresnel Effect
The dependence of reflection on
angle is called the Fresnel effect.
Looking at the water at a
large angle we see a strong
reflection of the sky.
Looking straight down into the
water we see the bottom and
little reflection of the sky.
Challenge Question
Can you cast a shadow
on a mirror?
A) Yes
B) No
Shadows &
Mirrors
No
No shadow of
my arm on
the mirror.
Note: If mirror is dirty then
shadow is seen on the dust
Optics & Lighting
Part III:
Refraction
Elements of Optics
Reflection
Scattering
Light Source
Refraction
Eye-Brain
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.
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.”
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.
Demo: Invisibility
Pour oil on frosted glass plate; see
through the glass
Removing scratches
Waxing a surface doesn’t remove
scratches, it just matches refraction.
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.
A
B
C
WEDGE
Refraction in a Wedge (2)
Which path does
light ray when it
reaches the
opposite side?
A
B
A) Path A
B) Path B
C)Path C
C
WEDGE
Refraction in a Wedge (2)
Path B
Notice that it bends
away from the
perpendicular going
back out of the glass.
By reciprocity the path of
the light ray is the
same if we reverse the
direction of the arrows.
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: Lenses
Light rays converge or
diverge by refraction
passing through a lens.
Concave lens
Convex lens
Focusing and Shadows
When refraction focuses
light to create bright
areas, it also removes
light and creates
shadowed areas.
Dark
Bright
Caustics
Caustics 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
Focusing and Shadows
Water is
transparent
yet the
droplets cast
shadows due
to refraction.
Heat Shimmer and Mirages
http://www.youtube.com/watch?v=9cdrLG9xx0Y
Mirages
Mirages are caused by
the refraction of air
because hot air has
lower optical density
than cold air.
Cool Air
Hot Air
Camera Lens
Using a lens allows for light to be focused
on a screen or camera film.
No image (Diffuse)
Camera with lens
Image inversion
An object
located
past the
focal point
is inverted
by a
convex
lens.
Demo: Real Image of Convex Lens
Image formed by convex lens can be
observed on a screen.
Hooke’s Micrographia
In 1665, Robert Hooke produced detailed
illustrations using the newly discovered
instrument: the microscope.
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
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."
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.
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
Refraction in Aquariums
Seeing around
the side of log
Mirror reflection
of sculpture
Refraction in Aquariums
Different views
on front and
side walls due
to refraction
Total internal
reflection off
side wall
Fiber Optics
Total internal reflection
causes light to reflect inside a
solid glass tube.
Demo: Laser in Water Stream
Total internal reflection
causes light to reflect
inside a stream of water.
Laser
Next Lecture
Scattering
Homework #12
Recreating Cameras and Lights in Maya
Due Tuesday, May 8th (Next week)
Please turn off and return the clickers!