Upcoming Deadlines Homework #12 – Lighting a Scene in Maya Due Thursday, December 1 st (This week) 20 points (10 points if late) Homework #13 – Creating Stereoscopic 3D Images Due Thursday, December 8 th (Next week) 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 Light the scene created in your previous homework assignment using one, two, and three-point lighting. Created by Candace Downey One-point Lighting: Light the scene with a single bright spot light on the left side; this is your key light.

Homework #12 Created by Candace Downey Two-point Lighting: Add a dim fill light on the right side to soften the shadows created by the key light. Three-point Lighting: Add a bright rim light behind the letters to accentuate their edges from the dark background.

Homework #12 Created by Candace Downey Render the three scenes, save each image, and upload them to your blog. Due by 8am on Thurs., December 1 st 20 points (if late, 10) All Assignments and Extra Credit must be turned in by 5pm on Thursday, December 8 th (last day of classes)

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.

Survey Question How much time did last week’s homework (Building a Scene in Maya) take you to complete? A)Less than an hour B)Between one and two hours C)Between 2 and 4 hours D)Over four hours E)Didn’t finish that assignment

Finding the Highlight A B C D: None of these Lamp Where does Albert see the highlight reflected off this metal block? 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 + 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)

Original Image Mirror Review Question A) Concave Mirror

Review Question The dependence of reflection on angle is called the ______ effect. Looking straight down into a pool of water we see little reflection of the sky. Looking at the water at a large angle we see a strong reflection of the sky.

Review Question Small angle Large angle Weak Reflection Strong Reflection The dependence of reflection on angle is called the ______ effect. A)ReflexB) RefluxC) Rephase D) FresnelE) What-The-Flux

Fresnel Effect The dependence of reflection on angle is called the Fresnel effect. Looking straight down into a pool of water we see little reflection of the sky. Looking at the water at a large angle we see a strong reflection of the sky.

Optics & Lighting Part 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.

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 A B)Path B C)Path C A B C WEDGE

Path B The 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

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.

Camera Lens Using a lens allows for light to be focused on a screen or camera film. No image (Diffuse)Camera with lens

Demo: Real Image of Convex Lens Image 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."

Focusing and Shadows Bright Dark When refraction focuses light to create bright areas, it also removes light and creates shadowed areas.

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

Total Internal Reflection When refraction angle exceeds 90º the light does not cross the surface. Refracted Reflected

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

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

Separating Colors Blue wavelength of light refracts slightly more than the red, creating rainbows. Glass Prism Water Droplet

Rainbows Rainbows are formed by refraction from many, many raindrops. The red part is always above the blue part.

Double Rainbow Primary Secondary

Atmospheric Perspective Objects in the distance have a bluish, unsaturated color due to atmospheric scattering of blue light (same as blue sky).

Atmospheric Perspective Example

Mt. Hadley

View From EVA 3

Dave Scott on the Slopes of Mt. Hadley Delta Pan

Apollo 15 Landing Site Mt. Hadley (14,000 ft) Photographer 20 km Mt. Hadley Delta (11,000 ft)

Mauna Loa (~height as Mt. Hadley) from ~20 km away

“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 Scattering Scattering by particles, such as droplets of fog, of micron size. 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 Notice the shadows Particles in Mie scattering are often transparent or highly reflective.

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.

Rayleigh Scattering Sky is blue due to Rayleigh scattering of sunlight in the atmosphere. When sunlight passes through a very thick layer all the blue is scattered out and we’re left with yellowish red.

Underwater Perspective Water 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.

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

Call of Duty: Black Ops (2010) Atmospheric effects are important for creating the right look for this snow level in the game.

Next Lecture Seeing Color HW #12 Due Thursday Please turn off and return the clickers!