159.235 Representation and Graphical Programming.


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159.235 Design and Graphical Programming. Address 32 - Enlightenment Section 2 - Worldwide Models. Worldwide Brightening. Extends the Neighborhood Light Model to include: Reflection (one item in another) Refraction (Snell's Law) Straightforwardness (better model)
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Slide 1

159.235 Graphics & Graphical Programming Lecture 32 - Illumination Part 2 - Global Models Graphics

Slide 2

Global Illumination Extends the Local Illumination Model to include: Reflection (one item in another) Refraction (Snell’s Law) Transparency (better model) Shadows (at point, check every light source) Antialiasing (ordinarily means supersampling) Graphics

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Wireframe View of a Test Scene Orthographic perspective from above Graphics

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Test Scene High quality rendering of test scene. Note : Mirror and chrome teapot. Shadows on floor. Sparkling floor. Design

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Locally Illuminated Test Scene Ambient term just Graphics

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Locally Illuminated Test Scene Phong shading. Encompassing and Diffuse terms just Notes : Highlight on divider from light is in the wrong place; screen space introduction. We can\'t enlighten the lights with the light sources – wrong side ! Representation

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Locally Illuminated Test Scene Phong shading. Encompassing, diffuse and Specular terms. Illustrations

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Locally Illuminated Test Scene Flat shading. Note : Mach groups. Representation

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Locally Illuminated Test Scene Gouraud shading. Surrounding, diffuse and Specular terms. Note: ancient rarities on divider. Representation

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Solution to Gouraud Artifacts Gouraud shading. Re-triangulated lattice. Design

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Comparison Flat Gouraud Phong Coarser cross section Graphics

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Use Local Illumination No. In our test scene, we can’t speak to : Mirror Chrome teapot. Glossy floor Shadows with nearby brightening. Representation

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Kajiya’s Rendering Equation Viewer is at point x , looking toward point x . I ( x,x ) decides measure of light touching base at x from x  g ( x,x ) is a geometry term, = 0 when x  is blocked, generally = weakening factor 1/r 2 (or 1/(s+k)) ( x,x ) is the measure of light transmitted from x  to x. ( x,x , x ) is the part of light reflected and scattered off x  to point x from point x  The indispensable S is over every such point (x ") on all surfaces. Illustrations

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Global Illumination Two routines : View subordinate strategies. Ascertain the perspective from the camera with worldwide enlightenment. Recursive beam following. View autonomous routines. Tackle lighting for the whole scene. Radiosity arrangement. Design

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View Dependent Methods Loop round the pixels….. Useful for lighting impacts which have an in number reliance on perspective area : Specular highlights. Reflections from bended surfaces. Just a little number of articles should be considered in the meantime. Poor when numerous articles should be viewed as E.g diffuse communications (eg. shading dying). Illustrations

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View Independent Methods Loop round the scene… Good when some (everything) items need to be considered at same time. Diffuse between reflections. Poor when shading has solid reliance on perspective area. Specular reflection. Representation

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Scene Eyepoint Window Recall : Ray Casting Involves anticipating a fanciful beam from the focal point of projection (the viewers eye) through the focal point of every pixel into the scene. The principal question the beam meets decides the shade. Design

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Whitted’s calculation Fire off optional beams from surface that beam crosses. Towards Light Source(s) : shadow beams. L (shadow sensors) In the reflection heading : reflection beams, R In a course managed by Snell’s Law : transmitted beams, T   Graphics

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Recursive Ray Tree Reflection and Transmission Rays bring forth different beams. Shadow beams test just for impediment. The complete arrangement of beams is known as a Ray Tree. Light Source beam decides shade of current article. Perspective Graphics

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Recursive Ray Tree Reflection and Transmission Rays bring forth different beams. Shadow beams test just for impediment. The complete arrangement of beams is known as a Ray Tree. Representation

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Test Scene Ray tree profundity 1. Note just surrounding shade on mirror and teapot Graphics

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Test Scene Ray tree profundity 2. Note just encompassing shade on impression of mirror and teapot. Illustrations

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Test Scene Ray tree profundity 3. Note just surrounding shade on impression of mirror in teapot. Illustrations

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Test Scene Ray tree profundity 4. Note encompassing shade on impression of teapot in impression of mirror in teapot. Illustrations

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Test Scene Ray tree profundity 5. Illustrations

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Test Scene Ray tree profundity 6. Representation

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Test Scene Ray tree profundity 7. Representation

Slide 28

When to stop ? Need to know when to stop the recursion. Can characterize a settled profundity. Corridor presented versatile tree profundity control. Compute top level input of a beam to a pixels last esteem. Increase commitment of ray’s predecessors down the tree. Stop when beneath some limit, maybe stack flood. May miss real commitment along these lines (winnowed brilliant pt) Graphics

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Adaptive Tree Depth Control 0.3 Viewpoint 0.2 Graphics

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Adaptive Tree Depth Control 0.3 * 0.2 Viewpoint 0.2 * 0.2 Graphics

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Global versus Nearby Illumination In both an article hit by a beam, if lit by a light source, is lit up by a neighborhood enlightenment model, i.e with specular, diffuse & surrounding terms. Worldwide: a reflected beam, a shadow sensor, and a transmission beam (if suitable) are additionally thrown into the scene. Phong term just reflects light source. Need to change neighborhood enlightenment terms to standardize aggregate light values. Conflicting if nearby and worldwide specular terms utilized together as neighborhood term spreads light source, worldwide term does not. Representation

Slide 32

Increased reflectivity Phong specular term is held consistent Increased transmissivity Graphics

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Incorrect Result Effect of not normalizing reflection and transmission – light has all the earmarks of being made. Reflection & transmission = 100% Graphics

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Problems with Ray-Tracing A difficult issue with Ray following is beams are followed from the eye. Refraction is not physically amend. Shadow beams are thrown just to light sources Lights reflected in mirrors don\'t cast Shadows of straightforward items don’t display refraction. Still need neighborhood light for diffuse shading. Design

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Speeding up Ray Tracing Ray following is moderate, not continuous. Utilization suitable degrees for articles. Beam following is intrinsically parallel. Utilize thing supports – z-requested records, store nearest question per pixel. Utilize light support – z-requested rundown per light beam utilized for shadowing. Illustrations

Slide 36

Illumination Part 2 - Summary Reflection Refraction Transparency Shadows Antialiasing Acknowledgments - on account of Eric McKenzie, Edinburgh, from whose Graphics C

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