Upcoming Deadlines
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
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 #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).
Maya Render
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
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 #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.
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.
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
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!
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
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
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)
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
Mirages
Hot Air
Cool Air
A) RefractionMirages are caused by the refraction of air because hot air has lower optical density than cold air.
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?
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
Optics & LightingPart IV:
Scattering
Elements of Optics
Light Source
Refraction
ScatteringEye-Brain
Reflection
DW Consulting Example
Disco lights for Intel commercial
Basic Scattering
Some sunlight is scattered, making the fog visible.
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.
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.
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
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? ?
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.
Particle Sizes & Scattering
Tiny Particles (Rayleigh Scattering)
Small Particles (Mie Scattering)
Large Particles (Reflection/ Refraction)
Air
CloudBirds
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
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
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
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
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
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
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.
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.
Volumetric Lighting
Volumetric lighting is used to create the volume of scattered light, usually due to Mie scattering in dust or fog.
Scattering & Angle
Direction of light scattering is not random.
More lightLess light
ForwardBackward
Mie Scattering & Angle
Mie scattering is strongest in the forward and weakest backward directions.
Fog
Mie Forward Scattering
Fog
Drier Vent
Sun is behind the fog in this photo
Camera
Sun
Mie scattering from drier fog
Mie Backward Scattering
Fog
Drier Vent
Sun is behind the camera in this photo
Camera
Sun
Mie scattering from drier fog
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
Rayleigh Scattering & Angle
Rayleigh scattering is strongest in the forward and backward directions.It is weakest to the sides (90 degrees).
Gas fumes
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
Single vs. Multiple Scattering
Light rays may scatter multiple times, if the scattering medium is dense.
Light Fog
Heavy Fog
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.
Single Scattering in a Fish Tank
Flashlight
Single scattering produces a narrow beam of light.
Mie scattering by very dilute water/milk mix.
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
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.
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.
20%100% 80%
Optical Thickness
Total scattering depends on optical thickness.
40%100% 60%
Demo: Beaker on projector; fill with milky water
Shadows & Multiple Scattering
ShadowsWith multiple scattering the side opposite from the light can be in shadow.
Atmospheric Perspective
Objects in the distance have a bluish, unsaturated color due to combination of Rayleigh, Tyndall, and Mie scattering.
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
Atmospheric Perspective Example
Fog and Smog
Atmospheric perspective can remove all contrast for distant objects, turning them into silhouettes.
Notice clock face
“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
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.
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.
Next LectureSeeing Color
Homework #12Recreating Cameras and Lights in MayaDue Tuesday, May 8th (Next Tuesday)
Please turn off and return the clickers!
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