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Homework #12 –Cameras and Lights in MayaDue Tuesday, May 8th (Next week)20 points (10 points if late)

Homework #13 – Creating Stereoscopic 3D ImagesDue Tuesday, May 15th (Last day of classes)20 points (10 points if late)

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

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

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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

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Photo

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Homework #12The 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).

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Maya Render

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Homework #12To 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

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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)

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Homework #12Non-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.

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Final Exam

Final exam is on Tuesday, May 22nd from 1215 to 1430 in this classroom.

Final Exam will have of 10 short essay questions on material covered in lecture.Final exam counts for 50 points.

You may bring one page of notes double-sided (or two pages single-sided) to the exam.

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Final Exam

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

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Special Event

PIXAR presentation on "Brave" in Washington Square Room 109 at 3:30pm today.

Go immediately after class if you hope to get a seat!

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Survey Question

From which of these assignments did you learn the most:

A) Term papers

B) Homeworks using Tracker

C) Stop-motion animation homeworks

D) Homeworks using Maya

E) Reverse video reference

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Review Question

Which path does light ray take after entering the water?

A) Path A

B) Path B

C) Path C

D) Path D

D

CBA

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Law of Refraction

C) Path C

Angle is smaller in the denser material.

The light ray bends but does not cross the normal (line perpendicular to the surface)

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Review QuestionWhat looks like a pool of water in this photo is actually a mirage image of the sky created due to the desert heat.

Mirages are produced by:

A)RefractionB)ReflectionC)ScatteringD)MiraclesE)Myopia

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Mirages

Hot Air

Cool Air

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

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Review Question

Natural lighting underwater is primarily from overhead because sunlight cannot enter the water at more than about a 45 degree angle.

True or False?

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Total Internal Reflection

True. For the same reason you can only see the sky from underwater when looking up at more than about a 45 degree angle.

See skyMirror

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Optics & LightingPart IV:

Scattering

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Elements of Optics

Light Source

Refraction

ScatteringEye-Brain

Reflection

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DW Consulting Example

Disco lights for Intel commercial

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Basic Scattering

Some sunlight is scattered, making the fog visible.

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Scattering Out & Scattering In

To this viewer, the fog has scattered out some of the light so the sun isn’t as bright

To this viewer, the fog has scattered in some light so the fog is visible.

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40%

10%

For example, if 40% of the light is scattered and 10% is absorbed then 50% directly reaches viewer.

100% 50%

Scattering vs. Absorption

Scattering is a deflection of the light.Absorption is an elimination of light.

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40%

10%

Extinction is 50% in both cases.

100% 50%

Extinction

Extinction defined as absorption plus scattering.

10%

40%

100% 50%

40% scattered10% absorbed

10% scattered40% absorbed

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Demo: Scattering vs. AbsorptionBeakers filled with water placed on overhead projector.Beaker has drop of white ink, the other has a drop of black ink.

What is seen on the screen? ?

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Demo: Scattering vs. AbsorptionGlass dishes filled with water placed on overhead projector.One dish has drop of milk, the other has a drop of black ink.

Projected image has two dark spots.

Black ink absorbs light.White ink scatters light.

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Particle Sizes & Scattering

Tiny Particles (Rayleigh Scattering)

Small Particles (Mie Scattering)

Large Particles (Reflection/ Refraction)

Air

CloudBirds

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Particle Sizes & Color

Tiny Particles – Scatter blue light the most, red the least; white light scattered with a hue shift to blue.

Air molecules

Gas fumes

Fine smoke

Particles smaller than wavelength of visible light.

Rayleigh Scattering

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Rayleigh Scattering by Color

0 200 nm 400 nm

Sca

tter

ing

Str

engt

h

Particle Size

For tiny particles (under 400 nm) scattering is strongest for blue light and weakest for red light.

Blue light: 440 nmGreen light: 550 nmRed light: 660 nm

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Tyndall Scattering

Tyndall scattering is very similar to Rayleigh scattering since both are the scattering of light (especially blue light) by very small particles.

Opalescent glass

Blue iris

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Demo: Aerogel Opalescence

Aerogel is ultralight, hard foam made from SuperGlue.

Scattering makes aerogel look blue while the transmitted light is yellow.

Flashlight shines white light on a piece of aerogel

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Particle Sizes & Color

Small Particles – Scattering of hues varies with particle size, usually averaging out to white.

Clouds

White paint

Milk

Particles comparable to wavelength of visible light.

Mie Scattering

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Mie Scattering by Color

400 nm 800 nm 1200 nm

Sca

tter

ing

Str

engt

h

Particle Size

For small particles Mie scattering strength varies greatly with the particle size.

Since particles tend to be a mix of sizes, all hues are scattered equally resulting in white.

Blue light: 440 nmGreen light: 550 nmRed light: 660 nm

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Particle Sizes & Color

Large Particles – Reflect light off the surface or, if transparent, refract and transmit light.

Rain

Sand

Confetti

Particles much larger than the wavelength of visible light.

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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.

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Volumetric Lighting

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

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Scattering & Angle

Direction of light scattering is not random.

More lightLess light

ForwardBackward

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Mie Scattering & Angle

Mie scattering is strongest in the forward and weakest backward directions.

Fog

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Mie Forward Scattering

Fog

Drier Vent

Sun is behind the fog in this photo

Camera

Sun

Mie scattering from drier fog

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Mie Backward Scattering

Fog

Drier Vent

Sun is behind the camera in this photo

Camera

Sun

Mie scattering from drier fog

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Sun Rays

To camera

To camera

Intensity of sun rays varies with the angle between sun and viewer.

Notice that the light on the ground is bright even though the ray’s intensity appears to taper off along the sun ray.

Mie scattering by fog mist

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Rayleigh Scattering & Angle

Rayleigh scattering is strongest in the forward and backward directions.It is weakest to the sides (90 degrees).

Gas fumes

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Brightness of the Sky

The darkest part of the sky tends to be about 90 degrees from the direction of the sun.

Rayleigh scattering by air molecules

From Sun

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Single vs. Multiple Scattering

Light rays may scatter multiple times, if the scattering medium is dense.

Light Fog

Heavy Fog

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Demo: Scattering in a Fish Tank

Single versus multiple scattering is nicely shown by shining a flashlight into an aquarium filled with clean water then adding more and more milk.

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Single Scattering in a Fish Tank

Flashlight

Single scattering produces a narrow beam of light.

Mie scattering by very dilute water/milk mix.

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Single Scattering in a Fish Tank

Flashlight

Intensity differences due to scattering angle (i.e., near the light we have more forward scattering).

To camera To camera

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Multiple Scattering in a Fish Tank

Flashlight

Multiple scattering produces a diffuse beam of light.

Hue shift from white (near flashlight) to orange-red on the opposite side.

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Scattering in a Fish Tank

To camera

To camera

With single scattering only particles in the direct beam are scattering the light.

With multiple scattering particles outside the beam are illuminated by light scattered from out of the beam.

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20%100% 80%

Optical Thickness

Total scattering depends on optical thickness.

40%100% 60%

Demo: Beaker on projector; fill with milky water

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Shadows & Multiple Scattering

ShadowsWith multiple scattering the side opposite from the light can be in shadow.

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Atmospheric Perspective

Objects in the distance have a bluish, unsaturated color due to combination of Rayleigh, Tyndall, and Mie scattering.

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Atmospheric Perspective

Far away mountains can have a bluish ting due to blue light scattered in by Rayleigh scattering

Weak scattering but big optical depth

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Atmospheric Perspective Example

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Fog and Smog

Atmospheric perspective can remove all contrast for distant objects, turning them into silhouettes.

Notice clock face

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“Perspective of Color”

Not only did Leonardo da Vinci make good use of what he called “Perspective of Color” but he also correctly predicted that this is why the sky is blue.

The Virgin of the Rocks, 1482

The Virgin and Child with Saint Anne, 1510

La Gioconda, 1503-06

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Underwater PerspectiveWater 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.

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Sunrise & Sunset

At sunrise and sunset the rays from the sun pass through a thick layer of atmosphere so Rayleigh scattering removes much of the blue light.

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Next LectureSeeing Color

Homework #12Recreating Cameras and Lights in MayaDue Tuesday, May 8th (Next Tuesday)

Please turn off and return the clickers!