CSC 418 Computer Graphics n n n Raytracing
- Slides: 51
CSC 418 Computer Graphics n n n Raytracing Shadows Global Illumination
Local vs. Global Illumination Local Illumination Models n e. g. Phong n Model source from a light reflected once off a surface towards the eye n Indirect light is included with an ad hoc “ambient” term which is normally constant across the scene Global Illumination Models n e. g. ray tracing or radiosity (both are incomplete) n Try to measure light propagation in the scene n Model interaction between objects and other objects and their environment
All surfaces are not created equal n n Specular surfaces – e. g. mirrors, glass balls – An idealized model provides ‘perfect’ reflection c Incident ray is reflected back as a ray in a single direction c No scattering (unrealistic) Diffuse surfaces – e. g. flat paint, chalk – Lambertian surfaces – Incident light is scattered in all directions c Also unrealistic for most surfaces
Categories of light transport n n Specular-Specular-Diffuse-Specular
Real surfaces are more complex…
Ray Tracing n n Traces path of specularly reflected or transmitted (refracted) rays through environment Rays are infinitely thin Don’t disperse Signature: shiny objects exhibiting sharp, multiple reflections
Ray Tracing n Unifies in one framework – Hidden surface removal – Shadow computation – Reflection of light – Refraction of light – Global specular interaction
Raytracing slides borrowed from…
Ray tracing setup
Ray does not intersect objects
Ray hits object
Shadow test
Point in shadow n With a simple lighting model, apply the ambient term for the shadow region
Reflected ray is sent out from intersection point
Reflected ray has hit object n n Local illumination model calculated where ray intersects with second object Result carried back to origin of ray on first object, contributes to object’s colour
Transmitted ray generated for transparent objects
Transmitted ray hit object n n Local illumination model calculated where the ray hit object Result carried back to the point of first intersection
No reflection
Single reflection
Double reflection
Ray Tracing Deficiencies n n n Local specular illumination model spreads rays in specular reflection, but global model doesn’t Ignores major light transport mechanisms – Interaction of diffuse surfaces Intersection computation time is very long
Ray Tracing Efficiency Improvements n n Bounding volumes Spatial subdivision – Octrees – SEADS – BSP
Ray Tracing Improvements: Image Quality n Backwards ray tracing – Trace from the light to the surfaces and then from the eye to the surfaces – “shower” scene with light and then collect it – “Where does light go? ” vs “Where does light come from? ” – Good for caustics
Ray Tracing Improvements: Image Quality n n Cone tracing – Models some dispersion effects Distributed Ray Tracing – Super sample each ray – Blurred reflections, refractions – Soft shadows – Depth of field – Motion blur
Radiosity n n Diffuse interaction within a closed environment Theoretically sound View independent No specular interactions
Global Illumination
Direct light is only part of the story
Ambient light
Lambertian Reflection and Colour Bleeding
Radiosity
Radiosity Equation
Form Factors
Techniques for Calculating Form Factors
Techniques for Calculating Form Factors
Where to next? n The general rendering equation (not part of this course!) n Next class…Curves and Surfaces
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- How does raytracing work
- Graphics monitor and workstation in computer graphics
- Computer graphics chapter 1 ppt
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- Intelremotemond
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- Bayou distributed system
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- Angel computer graphics
- What is viewing in computer graphics
- Graphics display devices
- Exterior clipping
- Shear transformation in computer graphics
- Shader computer graphics
- Difference between scan conversion of ellipse vs circle
- Rigid motion definition
- Region filling algorithm in computer graphics
- Dda algorithm advantages and disadvantages
- Polygon fill algorithm
- Raster scan display and vector scan display
- Computer graphics
- Dda line drawing algorithm
- Introduction to hidden surface removal
- Achromatic light in computer graphics
- Interactive picture construction techniques
- Uniform scaling in computer graphics
- Uniform scaling in computer graphics
- Orthogonal projection in computer graphics
- Logical input devices in computer graphics