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### Transcript of Refractions, Reflections and Caustics : Basic Concepts Lecture #15 Thanks to Henrik Jensen, John...

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• Refractions, Reflections and Caustics : Basic Concepts Lecture #15 Thanks to Henrik Jensen, John Hart, Ron Fedkiw, Pat Hanrahan, Rahul Swaminathan, Ko Nishino
• Slide 2
• Reflection and Refraction Water Air Vertex Normal N Reflection Refraction
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• Snells Law Incoming = Reflected sin()/sin() = Refractive Index (material dependent) Refractive index inversely proportional to speed of light (Huygens Principle) MaterialRefractive Index Air1.0003 Water1.333 Glycerin1.473 Immersion Oil1.515 Glass (Crown)1.520 Glass (Flint)1.656 Zircon1.920 Diamond2.417 Lead Sulfide3.910
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• Reflection
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• Really starts to be noticeable at less than 10-15 from the surface.
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• Fresnel Term Fresnel Term as found in text books is F = (sin(-)/sin(+)) + tan(-)*tan(+) Returns good results for strong reflecting water surfaces
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• Approximated Fresnel Term F 0 = (N-1) 2 /(N+1 )2 is a minimum of incoming light parallel to the normal of the surface. F = F 0 +(1- cos()) 5 * (1- F 0 ) is a value between 0 and 1 depending on the angle between the incoming ray and the surface normal. e.g. F 90 = 1, if the incoming ray is parallel to the surface, all light is reflected.
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• Designed to reflect all light eventually to Observer.
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• Anti-reflective Coatings One of the most significant advances made in modern lens design, whether for microscopes, cameras, or other optical devices, is the improvement in antireflection coating technology. Reduce unwanted, stray reflections Use material coatings on glass to reduce reflection and maximize transmission. Take advantage of destructive light interference.
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• Anti-reflective Coatings Magnesium fluoride very commonly used on Lenses, Microscopes
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• Refractions or Reflections?
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• Refractions or Reflections Confusion Why do you see shiny roads when they are diffuse and are not wet? Why do you see apparent reflections in deserts? Where else do you see apparent reflections? Do you see reflections above objects???
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• Used in Endoscopy, Communications
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• Water Drops : Refractions + Reflections
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• A Drop and its Environment. World in a drop
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• Shapes of falling drop
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• Refraction and Reflection (r)(r) (s)(s) ^ n ^ ^ L e L e i i s ^ r ^ i v ^ n ^ q n z a A B a Pin hole r Image plane q q q i p ^ q z ^
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• Refraction
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• Geometric mapping fov=165 degrees
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• Experiments: Refraction Experimental setup Calculated corners are in green
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• Photometry of Refraction
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• Plot of Transmitted Radiance
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• Experiment: Photometry of Refraction Experimental Setup Renderedactual image difference image
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• Reflection
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• Photometry of Reflection
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• Reflection vs. Refraction 0 0.20.40.60.81 0 0.20.40.60.81 0 0.2 0.4 0.6 0.8 1 refraction reflection internal reflection distance from the center radiance L
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• Rendering a Rain drop
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• World in a Rain Drop Low Library Pupin Hall
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• Tired of water drops? Wait, theres more
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• Rainbows : Refractions + Reflections + Wavelength of Light
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• Visible Light Wavelength Dispersion
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• Can you see rainbows during midday?
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• Why are there two rainbows? Are there only two rainbows?
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• Why the color pattern?
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• Bright Sky under and Dark above the Rainbow Photo by Ben Lanterman taken immediately after a heavy rainstorm when the air was quite saturated at 4PM.
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• Caustics: Bunching up Reflections or Refractions
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• What is wrong with this rendering? What is wrong with this rendering?
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• With caustics With caustics
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• Looking at Water Light is reflected and refracted at the same time There is a light pattern on the ground (Caustics)
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• Shafts of light and caustics: http://nis-lab.is.s.u-tokyo.ac.jp/~nis/cdrom/pg/pg2001_iwa.pdf
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• Caustics by Refraction Light is refracted by the water surface Some spots are stronger illuminated then others
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• Light rays through a water surface Bright areas caused by bunching of refracted rays dark
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• Water-filled glass spheres to focus or condense candlelight onto small areas ( 1800s )
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• Graphics Definition Create nice pictures with translucent objects and render nice effects on diffuse surfaces. Create nice pictures with translucent objects and render nice effects on diffuse surfaces.
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• Caustics in Cornell Box
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• Modeling and Animating Water Surfaces
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• Caustics by Reflections
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• Reflections and Caustics : Catadioptric Imaging + Refractions/Reflections and Caustics: Photon Mapping Lecture #16 Thanks to Henrik Jensen, John Hart, Ron Fedkiw, Pat Hanrahan, Rahul Swaminathan, Ko Nishino