Upcoming Deadlines

Upcoming Deadlines

Second Term PaperWednesday, 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.

Created by Candace Downey

Render the scene, save the image, and upload it to your blog.

Due by 8am on Monday, November 30th.20 points (if late, 10)

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 EventAnimation Show of ShowsDecember 7th (Monday)At 7:30 PM

Morris Dailey Auditoriumin Tower HallFREE

Optics & LightingPart II:

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.

CausticsCaustics 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.

Image

Actual

Image

Actual

Observer sees image

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

Air

Water

Air

Glass

Air

Diamond

n = 1.3

n = 1.0

n = 1.5

n = 1.0

n = 2.4

n = 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: 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 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

Mirages

Mirages are caused by the refraction of air because hot air has lower optical density than cold air.

Hot Air

Cool Air

Total Internal Reflection

When refraction angle exceeds 90º the light does not cross the surface.

Refracte

d

ReflectedReflected

Demo: Total Internal Reflection

Just below critical angle

Past the critical angle all the light is internally reflected.

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 OpticsTotal internal reflection causes light to reflect inside a solid glass tube.

Lenses

Concave lens shrinks its image

Convex lens magnifies its image

Curvature of a lens surface produces a continuous, variable angular refraction.

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 CameraSmall 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.

ETGWRPOCVMXSRYUQBNEHDThis works best if you

remove any corrective lenses, such as contacts and eyeglasses.

Camera ObscuraThe 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 coin-sized hole in one wall. An image of the outside world appears projected, upside down and reversed right-to-left, onto a wall opposite the opening.

Diffuse light

Giant CameraCamera obscura with a projecting

mirror.

Next to the Cliff House, San Francisco

MirrorMirror

Johannes Vermeer (1632-75)

The Music Lesson

Common elements in his paintings and ray tracing analysis suggest that this great Dutch artist may have built a camera obscura in his studio.

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

Image is formed upside-down on the retina of the eye.

The eye’s lens changes shape to focus the image onto light sensitive cells of retina.

Visual AcuityIf 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

AstigmatismAstigmatism 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 LightDigital cameras, such as in cell phones,

are sensitive to infrared light, such as from a remote control or any hot object.

MicrowaveTransmitter

MicrowaveReceiver

Separating Colors

Blue 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

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 PerspectiveObjects 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 ScatteringDirect scattering by suspended particles, such as dust, fog, etc.

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 Examples

Volumetric Lighting

Volumetric lighting is used to create the volume of scattered light, usually due to Mie scattering.

Next LectureSeeing Color

No class this Wednesday butSecond Term Paper due on Wednesday

Please return the clickers!