Happy Cinco de Mayo

Directed by Friz Freleng from a story by Warren Foster. Animation by Gerry Chiniquy and voices by Mel Blanc.Won the Oscar for Best Short Subject (Cartoons) in 1956.

Upcoming Deadlines

Homework #13 – Creating Stereoscopic 3D ImagesDue Monday, May 17th (Last day of classes)20 points (10 points if late)

Final Exam is at 12:15 on Wednesday, May 19th in this room.

All Assignments and Extra Credit must be turned in by 5pm on Wednesday, May 19th

There are no more furlough days for this class this semester.

For full schedule, visit course website:ArtPhysics123.pbworks.com

Pick up a clicker, find the right channel, and enter Student ID

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 double-sided (or two pages single-sided) to the exam.

Special Campus Event

Interview with Kathy Altieri, DreamWorks Animation artistTuesday, May 11th at 2:30 p.m.Morris Dailey Auditorium (Tower Hall)

http://www.youtube.com/watch?v=vkwZ9kzrMN0

Activating your Clicker

* Turn on your clicker.* Enter the channel number or letter for

joining this class. Hit Enter/Send key.* Clicker should read AP123S258* Type in your student ID; hit

Enter/Send.Clicker is now ready to use; leave it on.Hit any key to wake the clicker from sleep mode.

Survey QuestionIn the last homework assignment you will be re-coloring photos for 3D

effects.How much experience do you have using Adobe Photoshop?

A) Never used itB) Have used it only a little bitC) Use it regularlyD) I am a Photoshop God

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 Question

D) Lambert

A Lambert surface scatters light diffusely so under directional light it looks equally bright from all angles.

Johann Heinrich Lambert (1728–1777)

Review Question

What is the shape of the mirrors in these photos?

Concave Mirror

Convex Mirror

A)

B)

Review Question

OriginalImageMirror

Image in concave mirror is magnified when original is close to the mirror.

A) Concave Mirror

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.

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

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 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 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."

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 pinhole in a piece of cardboard. You’ll find that you can focus better when looking through the pinhole.

This 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.

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

Rayleigh Scattering

Sky is blue due to Rayleigh scattering of sunlight in the atmosphere.

When it passes through a very thick layer all the blue is scattered out and we’re left with yellowish red.

Volumetric Lighting

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

Alan Wake (2010)

Atmospheric effects are very important in Alan Wake, an upcoming game for Xbox 360.

http://www.youtube.com/watch?v=F3WfXAanKOs

Next LectureSeeing ColorNo homework due next week

Homework #13 due on Monday, May 17th

(Last day of class)

Please return the clickers!