Upcoming Deadlines Homework #12 – Lighting a Scene in Maya Due Thursday, December 1 st (This...

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Uniform Motion

Upcoming DeadlinesHomework #12 Lighting a Scene in MayaDue Thursday, December 1st (This week)20 points (10 points if late)

Homework #13 Creating Stereoscopic 3D ImagesDue Thursday, December 8th (Next week)20 points (10 points if late)

For full schedule, visit course website:ArtPhysics123.pbworks.comPick up a clicker, find the right channel, and enter Student ID1Homework #12Light the scene created in your previous homework assignment using one, two, and three-point lighting. Created by Candace DowneyOne-point Lighting:Light the scene with a single bright spot light on the left side; this is your key light.

2Homework #12Created by Candace DowneyTwo-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.

3Homework #12Created by Candace DowneyRender the three scenes, save each image, and upload them to your blog.

Due by 8am on Thurs., December 1st 20 points (if late, 10)

All Assignments and Extra Credit must be turned in by 5pm on Thursday, December 8th (last day of classes)4Final ExamFinal 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 semesters final exam.

You may bring one page of notes double-sided (or two pages single-sided) to the exam.5Survey QuestionHow much time did last weeks homework (Building a Scene in Maya) take you to complete?

Less than an hourBetween one and two hoursBetween 2 and 4 hoursOver four hoursDidnt finish that assignment

6Finding the HighlightABCD: None of theseLampWhere does Albert see the highlight reflected off this metal block?


Finding the HighlightLampAlbertCLight rays from point C reach Albert.8

Review QuestionMatte surfaces, such as paper and cloth, are typically rendered in computer graphics using which shading model?


Key + FillKey only


Review QuestionD) LambertA Lambert surface scatters light diffusely so under directional light it looks equally bright from all angles.Johann Heinrich Lambert (17281777)10Review QuestionWhat is the shape of the mirrors in these photos?Concave MirrorConvex Mirror



OriginalImageMirrorReview QuestionA) Concave Mirror12Review 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.13Review QuestionSmall angleLarge angleWeak ReflectionStrong ReflectionThe dependence of reflection on angle is called the ______ effect.ReflexB) RefluxC) RephaseD) FresnelE) What-The-Flux

14Fresnel 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.15Optics & LightingPart III: Bending & Scattering

16Global Illumination

Notice focusing of light through glass sphereWithout GIWith GIAdvanced computer graphics uses global illumination algorithms to compute a more physically realistic rendering of a scene.17RefractionLight rays bend (refract) passing from water to air, making objects appear to be shallower and closer to the observer.

ImageActualImageActualObserver sees image

18ReciprocityLaserLight bends the same way whether its entering the water or coming out of the water.This symmetry for light rays is called reciprocity.19Law 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.20Demo: Refraction thru a BlockLight is refracted entering the block and refracted back on leaving the block.

21Optical DensityAirWaterAirGlassAirDiamondn = 1.3n = 1.0n = 1.5n = 1.0n = 2.4n = 1.0Optical 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.22Demo: InvisibilityMineral 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.

23Refraction in a WedgeWhich path does light ray take after entering the glass wedge?


24Path 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.ABCWEDGERefraction in a Wedge25Lenses

Concave lens shrinks its image

Convex lens magnifies its imageCurvature of a lens surface produces a continuous, variable angular refraction.

26Demo: Concave Lenses

Curved surface of a concave lens causes light rays to diverge, dispersing the light and shrinking any images.27Demo: Convex LensesCurved surface of a convex lens causes light rays to converge, focusing the light and possibly magnifying images.

28Camera LensUsing a lens allows for light to be focused on a screen or camera film.

No image (Diffuse)Camera with lens

29Demo: Real Image of Convex LensImage formed by convex lens can be observed on a screen.

30Bokeh 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 wordboke( or ), which means "blur" or "haze."31Focusing and Shadows

BrightDarkWhen refraction focuses light to create bright areas, it also removes light and creates shadowed areas.32CausticsCaustics 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 caustics brightness.

Refraction causticsReflection caustics33Total Internal ReflectionWhen refraction angle exceeds 90 the light does not cross the surface.

RefractedReflectedReflected34Demo: Total Internal Reflection

Just below critical anglePast the critical angle all the light is internally reflected.35Demo: Total Internal Reflection

Prism demonstrates total internal reflection if the angle of incidence is large enough.No light escapes to this sideNo light escapes to this sideNo light escapes to this side36Looking up UnderwaterTry this when youre in the pool or the ocean next summer.

Looking straight up you see the sky but outside the 96 cone surface is like a mirror37Natural Lighting UnderwaterDue to total internal refraction sunlight never enters the water at more than about a 45 degree angle.

Image seen underwaterSun38Fiber Optics

Total internal reflection causes light to reflect inside a solid glass tube.39Separating ColorsBlue wavelength of light refracts slightly more than the red, creating rainbows.

Glass PrismWaterDroplet

40RainbowsRainbows are formed by refraction from many, many raindrops. The red part is always above the blue part.

41Double Rainbow

PrimarySecondary42Atmospheric PerspectiveObjects in the distance have a bluish, unsaturated color due to atmospheric scattering of blue light (same as blue sky).


Atmospheric Perspective Example

44Mt. Hadley

Mt. Hadley is 5 km high and 20 km away from the photographer in this composite of 500 mm images

View From EVA 3LEM is above and left of center, 4km away in this view with a 500 mm lens. The manmade object (about 18 feet tall) gives some scale to the image.Dave Scott on the Slopes of Mt. Hadley Delta

PanClick on the Pan link to see the full scanable panorama including Hadley Delta, Hadley and the Rille (1000 ft. deep).Even with the astronaut in the foreground, judging the height of the mountain is impossible. Apollo 15 Landing Site

Mt. Hadley(14,000 ft)Photographer20 kmMt. Hadley Delta(11,000 ft)Mauna Loa (~height as Mt. Hadley) from ~20 km away

ML is the distant peak. Scale comes from fence posts, road, clouds, and atmospheric scattering.

Perspective of ColorNot 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

51Light ScatteringMie ScatteringScattering 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.52Mie Scattering

Notice the shadowsParticles in Mie scattering are often transparent or highly reflective.53Suspended 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.54Rayleigh 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 were left with yellowish red.55Underwater 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.56Volumetric Lighting

Volumetric lighting is used to create the volume of scattered light, usually due to Mie scattering.57

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