Lec12 ImageGeneration s06

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Published on January 14, 2008

Author: Calogera

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Light and Rendering:  Light and Rendering CS5600 Computer Graphics Rich Riesenfeld Spring 2006 Lecture Set 12 Lighting Models:  Lighting Models Shading Schemes:  Shading Schemes Flat Shading: same shade to entire polygon Shading Schemes:  Shading Schemes Gouraud Shading: smoothly blended intensity across each polygon Shading Schemes:  Shading Schemes Phong Shading: interpolated normals to compute intensity at each point Bui Toung Phong Thesis Scan Convert Polygon P:  Scan Convert Polygon P Intensity Interpolation:  Compute by direction evaluation of illumination expression, whichever formula is being used Intensity Interpolation Using Average Normals:  Using Average Normals N = true (geometric) normal Using Average Normals:  Using Average Normals Using Average Normals:  Using Average Normals What should corner normals be?:  What should corner normals be? More generally, Relevant Light (unit) Vectors:  Relevant Light (unit) Vectors Point light source direction Surface Normal Reflection direction Viewpoint direction Computing R Vector:  Computing R Vector Computing R Vector:  Computing R Vector Computing R Vector:  Computing R Vector Flat (Cosine) Shading:  Flat (Cosine) Shading Compute constant shading function, over each polygon, based on simple cosine term Same normal and light vector across whole polygon Constant shading for polygon Flat (Cosine) Shading:  Flat (Cosine) Shading Where, , for unit N, L intensity of point light source diffuse reflection coefficient Intensity Interpolation (Gouraud):  Intensity Interpolation (Gouraud) Slide19:  Normal Interpolation (Phong) Slide20:  Normal Interpolation (Phong) Normalizing makes this a unit vector Illumination Formula (1/2):  Illumination Formula (1/2) Illumination Formula (2/2):  Illumination Formula (2/2) Where, a denotes ambient term d denotes diffuse term s denotes specular term O denotes object k denotes constant I denotes intensity Effect of Exponent Parameter:  Effect of Exponent Parameter As n increases, highlight is more concentrated, surface appears glossier Mach Band Illusion:  Mach Band Illusion Ex: Mach Band Illusion:  Ex: Mach Band Illusion Ex: Mach Band Illusion:  Ex: Mach Band Illusion Mach Bands measured signal perceived signal Mach Band Illusion:  Mach Band Illusion How can we avoid the illusion in this image? How do we make the fields appear flat? Mach Band Illusion:  Mach Band Illusion Ex: rotating colors eliminate effect Mach Band Illusion:  Mach Band Illusion Example (intensity fields are flat!) Lateral Inhibition:  Lateral Inhibition Mach Band Illusion is explained by Lateral Inhibition Neighboring visual sensors are connected When one fires, it inhibits its next door neighbors from firing Lateral Inhibition:  Lateral Inhibition How does Lateral Inhibition work? Eye sees only difference from surrounding area Eye is a differencing mechanism, a differentiator, an edge detector, a motion detector Simultaneous Contrast:  Simultaneous Contrast Simultaneous Contrast:  Simultaneous Contrast Simultaneous Contrast:  Simultaneous Contrast Simultaneous Contrast:  Simultaneous Contrast Simultaneous Contrast:  Simultaneous Contrast Georgia O’Keefe, “New York Street with Moon” Motion Illusion:  Motion Illusion Illusion Clips of Edward H. Adelson, MIT Illusions Clips of E. H. Adelson, MIT:  Illusions Clips of E. H. Adelson, MIT Illusions Clips of E. H. Adelson, MIT:  Illusions Clips of E. H. Adelson, MIT Motion Illusion:  Motion Illusion Illusion caused by saccadic eye movements Motion Illusion:  Motion Illusion Concentric Circles or Spirals?:  Concentric Circles or Spirals? Imposition of Assumptions:  Imposition of Assumptions Vasarely: Optical Art:  Vasarely: Optical Art Vasarely: Optical Art (2):  Vasarely: Optical Art (2) Vasarely: Optical Art (3):  Vasarely: Optical Art (3) Vasarely: Optical Art (4):  Vasarely: Optical Art (4) Two Categories of Shadows:  Two Categories of Shadows Two kinds of shadows to consider: study a flag pole The shaded side of the pole is under shadow The pole casts a shadow on the ground. Two Categories of Shadows:  Two Categories of Shadows Progress in Shadows(2):  Progress in Shadows(2) Eye at light source gives no shadows Separate eye and point source of light Do VSD twice: from light (mark stuff not visible) from eye (shade appropriately) Progress in Shadows:  Progress in Shadows Shadow Volumes (Frank Crow) Weiler-Atherton Intersect all polygons againts all others… Big process, not stable, conceptially elegant Progress in Shadows (3):  Progress in Shadows (3) Many algorithms, particularly Hechtbert’s “events” General problem: area lights (luminaires) and area blockers Answer can be found in 4D, or higher Slide53:  Soft Shadows Complicated structure Seek an analytic solution Point source Area source Simple Case: One Blocker:  Simple Case: One Blocker Analytic solution involves splines in 4 dimensions Slide55:  Diffuse Scene Direct lighting Indirect lighting Lighting Effects (1):  Lighting Effects (1) Multiple Lights Spectral Absorption Texture Surface Irregularities Transparency Refraction Lighting Effects (2):  Lighting Effects (2) Atmospheric Effects Subsurface Interaction Shadows Directional Variations (anisotropic) Reflections Environment mapping Lighting Effects (3):  Lighting Effects (3) Directional Light Color Bleeding Camera Effects Ray Tracing:  Ray Tracing Classical geometric optics technique Extremely versatile Historically viewed as expensive Good for special effects Computationally intensive Can do sophisticated graphics Ray Tracing:  Ray Tracing Screen-space point Film plane point in canonical view volume World-space ray Environment Mapping:  Environment Mapping Radiosity:  Radiosity Considers all light in entire environment Gives indirect lighting Every surface can be an “emitter” Big linear system to solve Radiosity:  Radiosity Break up sceen into a system of interacting polygons: Early Cornell Radiosity Image:  Early Cornell Radiosity Image Extraordinary image of indirect lighting. Image has color bleeding and warm glow Early Cornell Radiosity Image:  Early Cornell Radiosity Image End Light and Rendering:  End Light and Rendering 67 Lecture Set 12

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