Efficient Simulation of Light Transport in Scenes with Participating Media using Photon Maps- Henrik Wann Jensen Per H. Christensen

05’ Digital Image SynthesisPresented by Jen-Yuan Chiang

Issues addressed by the paper Realistic Volume Rendering The ability to simulate following effects:

Multiple Volume Scattering Color Bleeding between volumes and surfaces Volume Caustics

Multiple Scattering Single Scattering

Multiple Scattering

Color Bleeding

Without participating media With participating media

Caustics Surface Caustics

Light reflected from or transmitted through one or more specular surfaces strikes a diffuse surface.

Caustics Volume Caustics

Light reflected from or transmitted through specular surfaces and then scattered by amedium

Issues addressed in this paper Extends the method of photon mapping

to achieve the global illumination of scenes with participating media

Outline

Overview of Photon mapping for surfaces

Light transport in participating media Extending Photon Mapping to

Participating Media Results

Overview of Photon Mapping for Surfaces

Global Illumination technique Two-pass particle-tracing algorithm

First pass: Building the photon maps using photon tracing

Second pass: Rendering using these photon maps

First pass Photons emitted from light sources Simulate the transport of each photon Store photon in photon maps when it hits none

specular surfaces Direct map Caustics map Indirect map

Balanced kd-tree is used to handle photons

3 photon maps

Ex. LSSSDSSSSD

Caustic map Indirect map

Second Pass

Specular reflection

Direct Illumination

CausticsIndirect illumination

Second Pass Illumination at a point is divided into four parts

Specular reflection: ray tracing Direct illumination: direct map or ray tracing Caustics: caustics photon map Indirect illumination: indirect photon map

2

2

2

|cos|),(),(),(),,(

|cos|),(),,(

|cos|),(),,(

,,,S iiiciiiiidiio

S iiiiio

S iiiiio

dpLpLpLpf

dpLpf

dpLpf

Radiance Estimate Information of Photons

Position(p), power( ), incoming direction( ) pp

N

p

ppprr r

xxfxL

12

),(),,(),(

Outline

Overview of Photon mapping for surfaces

Light transport in participating media Extending Photon Mapping to

Participating Media Results

Light Transport in Participating media

x

Radiance L changes continuously from L(p,w) to L(q,w)

p q

x

Volume Scattering Emission

In-Scattering

Absorption

Out-Scattering

),()( xLx e

),()( xLx i

),()( xLx

),()( xLx

Absorption coefficient

Scattering coefficient

Volume Rendering Equation

Extinction coefficient

Ray marching

Ray Marching Computes the contribution from the medium by

dividing the ray into smaller segments

x

emission

in-scattering

extinction(assuming medium properties are the same through )

X0X1 X2

Xk

xx x x

x

Outline

Overview of Photon mapping for surfaces

Light transport in participating media Extending Photon Mapping to

Participating Media Results

Extending Photon Mapping to participating media

From for surfaces to for volumes Still 2 pass particle tracing algorithm

First pass: additional volume photon map

Second pass: rendering using ray marching

Volume Radiance Estimate Estimate radiance using volume photon

map

Volume Radiance Estimate for Ray Marching For each ray through the volume, we can get the

radiance caused by volume scattering by marching along the ray and cumulating every ),( wxL k

in-scattered radiance

single scattering (direct):by ray tracing

Multiple scattering (indirect):by volume radiance estimate

Outline

Overview of Photon mapping for surfaces

Light transport in participating media Extending Photon Mapping to

Participating Media Results

Features of Volumetric Photon Mapping

Can model- Homogeneous as well as non-homogeneous media. Isotropic as well as anisotropic media. Since decoupled from geometry (photons stored in k

d-tree), so capable of handling complex scene.

Some Results Anisotropic and non-homogeneous medium

Underwater Scene with Volume Caustics

Pseudo code for volume photon mapping

http://www-graphics.stanford.edu/courses/cs348b-competition/cs348b-05/abandoned/index.html

Thanks!