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Lights in the Phong Model

Learn how to compute and describe light sources in the Phong Model, including ambient, directional, point, and spot lights. Explore illumination techniques, properties, and influences on rendered images.

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Lights in the Phong Model

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  1. Lights in the Phong Model 1. How to compute these? 2. What are these?

  2. Light source direction: • Look around you … • The light in Seattle: Indirect • background, … ambient • Sun light: Direct, very far away • coming from a constant direction(independent of where you are) • Light bulb at home: Direct • closer, shines from a fixed point • Light from the projector/desk lamp • How would you describe this? credit: http://mynasadata.larc.nasa.gov/Radiation_Explanation.html credit: http://www.truebeyonddesign.com/products-page/ http://www.apartmenttherapy.com/ny/lighting/best-product-tolomeo-desk-lamp-001066

  3. What is Ambient Light? • Not in the real world! • Implementation dependent! • constant color added to illumination results • Maya scene file Rendered image Ambient light Material Property

  4. What about the Sun? • How would you describe the incoming light source for this scene? http://www.planetware.com/picture/kansas-cottonwood-falls-tallgrass-prairie-national-preserve-flint-hills-national-prairie-us-ks108.htm

  5. Directional Light • Direction is: • No position!! (where is the Sun?) • Light has no geometry and does not show up in final rendered image • Planes looks … flat  • Maya Scene Rendered image Directional Light

  6. What about the Light Bulb? • How would you describe the light source of these scenes? http://companyofburninghearts.wordpress.com/2010/03/18/mystic-clusters/ http://home.cogeco.ca/~richardastro2/

  7. Point Light • Position () • For every visible position () • is unique! • Illumination is a function of relative position to lights! • Maya Scene Different vector for each visible point Point Lights Rendered image

  8. Now, my desk lamp • How would you describe the light source of these scenes? http://www.how-to-refinish-hardwood-floors.wirze.com/ http://agreenliving.org/tag/concept-design/ http://www.mackayphotography.co.uk/light_pollution.htm http://0.tqn.com/d/drawsketch/1/0/N/J/eggsetup.jpg

  9. Spot Light • Direction + Position: • Pointing direction • As in point light, for each visible point is unique! • Cone angle (θ) defines illumination range θ Different vector for each visible point

  10. Maya Scene Cone boundaries Rendered image

  11. Spotlight bounds Illumination at this point is • Position: • Main direction • : cone angle • θ: regions of full illumination • angle to position for illumination • If θ< < Illumination drops off according to: θ Region: fully illuminated Penumbra Region: gradual drop off

  12. Drop off behavior P<1 p=0.1 P>1 p=0.2 Drop off p=1 p=20 p=30

  13. scene No drop off Penumbra region

  14. Implement Penumbra Region • For a visible position: • cos( If (cos( > cos( // < Full illumination else if (cos() < cos()) // > no illumination else Penumbra region θ A visibleposition

  15. Distance Attenuation • Illumination is a function of • d = distance between light and visible position!! • Physics tells us • Did not follow physics in the rest of the model! • WAY too dark!! • Generally: d

  16. How about ? • Let user specify each of thecomponents! OpenGL: Maya: Our ToyRayTracer:

  17. General form of Phong Our Ray Tracer implements:

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