Illumination and Shading Prof. Lizhuang Ma Shanghai Jiao Tong University

Contents Illumination Models Shading Models for Polygons Surface Detail Shadows Transparency Global Illumination Recursive Ray Tracing Radiosity The Rendering Pipeline

Ambient Light: :intensity of the ambient light :ambient-reflection coefficient: 0~1 Diffuse reflection: :point light source’s intensity :diffuse-reflection coefficient: 0~1 :angle: Illumination Models

Diffuse Reflection

Examples

– :light-source attenuation factor –If the light is a point source –Diffuse reflection: where is the distance the light travels from the point source to the surface Illumination Models

Examples

If an object’s diffuse color is where for the red component however, it should be generally where is the wavelength Colored Lights and Surfaces then

Specular Reflection

– : specular-reflection coefficient: 0~1 So, the Eq. can be rewritten as: Consider the object’s specular color: – : specular color The Phong Illumination Model

The Phong Model

The Phong Illumination Model

Examples

Calculating the Reflection Vector

The Halfway Vector

Multiple Light Sources If there are m light sources, then

Shading Models for Polygons Constant Shading –Faceted Shading –Flat Shading Gouraud Shading –Intensity Interpolation Shading –Color Interpolation Shading Phong Shading –Normal-Vector Interpolation Shading

Constant Shading Assumption –The light source is at infinity –The viewer is at infinity –The polygon represents the actual surface being modeled and is not an approximation to a curved surface: –Note that N.L,N.V are constant across the polygon face

Gouraud Shading

Gouraud v.s. Phong Shading

Phong Shading

Texture Mapping = Pattern Mapping

Bump Mapping & Displacement Mapping

Shadows If light I is blocked at this point If light I is not blocked at this point

Shadows If light I is blocked at this point If light I is not blocked at this point

Scan-Line Generation of Shadows

Shadow Volumes

Shadow

Transparency Interpolated transparency : transparency: 0~1 Filtered transparency :transparency color

Global Illumination Direct & indirect (reflected) light sources

The Rendering Equation – : intensity passing from to – : emitted light intensity from to – : intensity of light reflected from to from the surface at ( indirect light sources ) – : the distance between and – : all surfaces if is invisible from if is visible from

Recursive Ray Tracing surface normal reflected ray shadow ray transmitted ray

Recursive Ray Tracing surface normal reflected ray shadow ray transmitted ray

Traditional Ray Tracing

Ray Tracing + Soft Shadows

The Ray Tree Intensity of reflected ray Transmission coefficient :0~1 Intensity of transmitted ray

– : radiosity of patch i – : rate at which light is emitted form patch i – : reflectivity of patch i – : form factor (configuration factor) – : area of patch i Since Thus The Radiosity Equation

Rearranging terms Therefore Progressive refinement The Radiosity Equation

Radiosity vs. Ray Tracing Ray traced image. Original Image rendered with radiosity.

Computing Form Factors

Hemisphere

Hemicube

The Rendering Pipeline Local Illumination Pipelines –z-buffer and Gouraud shading –z-buffer and Phong shading –List-priority algorithm and Phong shading Global Illumination Pipelines –Radiosity –Ray tracing

Rendering Pipeline for z-buffer & Gouraud Shading

Rendering Pipeline for z-buffer & Phone shading

Rendering Pipeline for List-priority Algorithm & Gouraud Shading

Rendering Pipeline for List-priority Algorithm & Phong Shading

Rendering Pipeline for Ray Tracing