Precomputed Light Transport Indirect Lighting Many indirect - PDF document

Precomputed Light Transport Indirect Lighting • Many indirect lighting effects are subtle, yet crucial for visual realism. Examples are: – Soft shadow – Ambient occlusion 1

Ambient Occlusion • Ambient light is a very crude approximation to indirect reflections of surrounding objects. • What if a point can’t see much of its surrounding? From: Janne Kontkanen & Samuli Laine ACM I3D 2005 Soft Shadow from Environment Lighting Sen, Cammarano, Hanrahan, 2003 Sloan, Kautz, Snyder 2002 Shadows from point-lights Shadows from smooth lighting (precomputed radiance transfer) (shadow maps, volumes) 2

Beyond Monte Carlo Path Tracing? • Are global illumination solvers always time consuming? • What if the scene and the lights are static ? � Radiosity (view can changes!) • What if only the scene is static? Precomputed Light Transport • Three important papers to start with: – "Precomputed Radiance Transfer for Real-Time Rendering in Dynamic, Low-Frequency Lighting Environments" Sloan et al., SIGGRAPH 2002 – "All-Frequency Shadows Using Non-linear Wavelet Lighting Approximation" Ng et al., SIGGRAPH 2003. – "Triple Product Wavelet Integrals for All- Frequency Relighting" Ng et al. SIGGRAPH 2004 3

The following 8 slides are from Ren Ng’s SIGGRAPH 2003 presentation Relighting as Matrix-Vector Multiply ⎡ ⎤ P 1 ⎢ ⎥ P ⎢ ⎥ 2 ⎢ ⎥ P 3 ⎢ ⎥ � ⎢ ⎥ ⎢ ⎥ ⎣ ⎦ P N ⎡ ⎤ ⎡ � T T T 11 12 1 ⎤ M ⎢ ⎥ ⎢ L � 1 T T T ⎥ ⎢ ⎥ ⎢ 21 22 2 M L ⎥ = ⎢ ⎥ � 2 T T T ⎢ ⎥ 31 32 3 M � ⎢ ⎥ ⎢ � � � � ⎥ ⎢ ⎥ ⎣ ⎦ L ⎢ ⎥ � N ⎣ ⎦ T T T N 1 N 2 NM 4

Relighting as Matrix-Vector Multiply ⎡ ⎤ P • Output Image 1 ⎢ ⎥ P ⎢ ⎥ (Pixel Vector) 2 ⎢ ⎥ P 3 ⎢ ⎥ � ⎢ ⎥ • Input Lighting ⎢ ⎥ ⎣ ⎦ P (Cubemap Vector) N ⎡ ⎤ ⎡ � T T T 11 12 1 M ⎤ ⎢ ⎥ ⎢ L � 1 ⎥ T T T ⎢ ⎥ ⎢ 21 22 2 M L ⎥ ⎢ ⎥ = � 2 T T T ⎢ ⎥ 31 32 3 M � ⎢ ⎥ ⎢ � � � � ⎥ ⎢ ⎥ ⎣ • Transport ⎦ L ⎢ ⎥ � N ⎣ ⎦ T T T Matrix 1 2 N N NM Ray-Tracing Matrix Columns ⎡ ⎤ � T T T 11 12 1 M ⎢ ⎥ � T T T ⎢ ⎥ 21 22 2 M ⎢ ⎥ � T T T 31 32 3 M ⎢ ⎥ � � � � ⎢ ⎥ ⎢ ⎥ � ⎣ ⎦ T T T 1 2 N N NM 5

Ray-Tracing Matrix Columns ⎡ ⎡ ⎡ ⎤ ⎤ ⎤ � � � T T T T T T T T T 11 11 11 12 12 12 1 1 1 M M M ⎢ ⎢ ⎢ ⎥ ⎥ ⎥ � � � T T T T T T T T T ⎢ ⎢ ⎢ ⎥ ⎥ ⎥ 21 21 21 22 22 22 2 2 2 M M M ⎢ ⎢ ⎢ ⎥ ⎥ ⎥ � � � T T T T T T T T T 31 31 31 32 32 32 3 3 3 M M M ⎢ ⎢ ⎢ ⎥ ⎥ ⎥ � � � � � � � � � � � � ⎢ ⎢ ⎢ ⎥ ⎥ ⎥ ⎢ ⎢ ⎢ ⎥ ⎥ ⎥ � � � ⎣ ⎣ ⎣ ⎦ ⎦ ⎦ T T T T T T T T T N N N 1 1 1 N N N 2 2 2 NM NM NM Light-Transport Matrix Rows ⎡ ⎤ � T T T 11 12 1 M ⎢ ⎥ � T T T ⎢ ⎥ 21 22 2 M ⎢ ⎥ � T T T 31 32 3 M ⎢ ⎥ � � � � ⎢ ⎥ ⎢ ⎥ � ⎣ ⎦ T T T 1 2 N N NM 6

Light-Transport Matrix Rows ⎡ ⎤ � T T T 11 12 1 M ⎢ ⎥ � T T T ⎢ ⎥ 21 22 2 M ⎢ ⎥ � T T T 31 32 3 M ⎢ ⎥ � � � � ⎢ ⎥ ⎢ ⎥ � ⎣ ⎦ T T T N 1 N 2 NM Light-Transport Matrix Rows ⎡ ⎤ � T T T 11 12 1 M ⎢ ⎥ � T T T ⎢ ⎥ 21 22 2 M ⎢ ⎥ � T T T 31 32 3 M ⎢ ⎥ � � � � ⎢ ⎥ ⎢ ⎥ � ⎣ ⎦ T T T 1 2 N N NM 7

Rasterizing Matrix Rows Pre-computing rows • Rasterize visibility hemicubes with graphics hardware • Read back pixels and weight by reflection function Low-Frequency vs. All-Frequency Teapot in Grace Cathedral 8

The following slides are from Peter-Pike Sloan’s presentation at MSRA Terminology 9

Terminology Terminology 10

Terminology Related Work SH PRT SH PRT SH PRT SH PRT Sloan et al. 2002 Kautz et al. 2002 Deformable BTF+PRT BTF+PRT Deformable Bump mapping Bump mapping Gaussians Gaussians Sloan et al. 2003 Sloan et al. 2005 Sloan et al. 2005 Green et al. 2006 Wavelet Double Wavelet Triple Wavelet Double Subsurface Wavelet Double Wavelet Triple Wavelet Double Subsurface Ng et al. 2003 Ng et al. 2004 Wang et al. 2006 Wang et al. 2005 11