Research funded by GRR 1368501 Propagating the VLF

Research funded by: GR/R 13685/01 Propagating the VLF - Problems and Solutions II Insu Yu i. yu@cs. ucl. ac. uk Virtual Light Field Group vlfproject@cs. ucl. ac. uk University College London

Overview l Specular Transfer – – – l Caustics – – l Determination of reflected Direction Forward/Backward Transfer Discontinuity and Resampling What is caustics Holes & Jittering Propagation Issues – – Progressive propagation Effect of Parameter Adjustment VLF Project

Specular Reflection l What is Ideal specular reflection model ? – – – l All the incoming Energy (L) is reflected off the direction(R) of a surface Incidence angle (θi) equals the angle of specular reflection (θr) A Mirror Reflection How can we adapt this model on VLF ? VLF Project

Determination of reflected direction l Discrete ‘Uniformly Sampled Directions’ – Due to the Representation of Finite Directions, an Ideal reflected PSF direction can hardly be found PSF Directions (Quadrant) VLF Specular Reflection VLF Project

Nearest Vs Tri-linear Directions l Nearest direction – – Select closest direction to the reflected direction Works better on High Resolution Directions Finding Nearest PSF Direction VLF Project

Nearest Vs Tri-linear Directions (Cont’) l Tri-linear – – Select Three PSF direction which enclose the reflected Direction Transfer Incoming Energy to three Directions according to barycentric weights of each direction Glossy not perfect specular Tri-linear interpolated transfer introduce excessive blurring Tri-linear Transfer VLF Project

Forward Vs Backward Mapping l Forward mapping – – – Diffuse to Specular Transfer Shooting Energy from Sender to Receiver Miss-alignment of source to destination leads holes Holes Forward Mapping VLF Project

Forward Vs Backward Mapping (Cont’) l Backward mapping – – Trace a ray in Reflected Direction in back order One-to-One mapping UV uniform subdivision on receiver planes Need to use bilinear interpolation scheme to pull the radiance values Backward Mapping VLF Project

Discontinuities & Resampling l Specular Reflection is not jittered – – – Diffuse Surfaces are jittered multiple time Due to Directional Energy Transfer URM is updated only once where Diffuse to Specular Transfer occurs l Blocky discontinuities appear despite Trilinear transfer l Resample all TRM at end of propagation by backwards ray tracing Resampling VLF Project

Relation to Directions l Accuracy of Specular Transfer is proportional to the number of directions Light Field Ray Tracing Specular Reflection (ES*D) VLF Project

Caustics VLF Project

Caustics l Caustics comes free as in Specular to Diffuse Transfer VLF Project

Specular to Diffuse Transfer l Caustics present where Diffuse surface gathers energy from specular senders VLF Project

Holes and Jittering l Holes Artefact – – – l l Due to representation of Discretisation Directions Transfer from small reflector to large receiver Long distance between reflector and receiver Increase sampling density of directions More jittered samples for caustic VLF Project

Filtering l Filtering to achieve accuracy and avoid aliasing l Caustics on Diffuse map can be excessively Blurred & introduce light leaking – Require Adjustment of Gaussian Kernel Sigma l Possible to have higher resolution diffuse maps on caustic receivers l Can exploit additional map for caustics VLF Project

Propagation l Propagation Process over various iterations VLF Project

Progressive Propagation l Progressive propagation framework – – l Estimating unshot radiance Selecting shooting sources & managing swapping of maps Purging of unshot energy Zero-energy surfaces are never senders Other issue – Capping of scenes VLF Project

Scalability Test (Effect of parameters) l l l Various Polygons Various PSF Directions Various PSF Size & Tile Size l l Propagation time and on memory Dual Xeon 1. 7 Ghz VLF Project

Effect of parameters (Polygons) l Propagation time varies quadratically with the number of polygons (513 Direction, 8 x 8 Tiles, 64 x 64 Cells) The memory grows linearly with the number of polygons l TEST Scene l – – – One Emitter polygons 224 to 1736 5: 1 ratio of diffuse to specular surfaces VLF Project

Effect of parameters (Directions) l Increasing PSF Directions – Pros l l The greater accuracy is achieved Less jittering is necessary (overcome missing holes) – Cons l l l More memory usage Longer Propagation Time Linear Relationship between the number of direction and propagation time/memory Office Test Scene VLF Project

Effect of parameters (PSF/Tile Resolution) l Size of Tile/PSF resolution determine the speed of propagation & rendering l Increasing Resolution results in faster intersection searching but more memory & propagation time VLF Project

Question ? VLF Project