Lec12 ImageGeneration s06

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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