Carlos Ureña, Iliyan Georgiev
We present a method for uniformly sampling points inside the projection of a spherical cap onto a plane through the sphere's center. To achieve this, we devise two novel area-preserving mappings from the unit square to this projection, which is often an ellipse but generally has a more complex shape. Our maps allow for low-variance rendering of direct illumination from finite and infinite (e.g. sun-like) spherical light sources by sampling their projected solid angle in a stratified manner. We discuss the practical implementation of our maps and show significant quality improvement over traditional uniform spherical cap sampling in a production renderer.
Ibón Guillén, Carlos Ureña, Alan King, Marcos Fajardo, Iliyan Georgiev, Jorge López-Moreno, Adrian Jarabo
We present new methods for uniformly sampling the solid angle subtended by a disk. To achieve this, we devise two novel area-preserving mappings from the unit square [0, 1]^2 to a spherical ellipse (i.e. the projection of the disk onto the unit sphere). These mappings allow for low-variance stratified sampling of direct illumination from disk-shaped light sources. We discuss how to efficiently incorporate our methods into a production renderer and demonstrate the quality of our maps, showing significantly lower variance than previous work.
Iliyan Georgiev, Marcos Fajardo
A method that improves the visual fidelity of Monte Carlo renderings without increasing the sampling effort. By correlating the samples between pixels using specially constructed blue-noise masks, the method minimizes the low-frequency content in the distribution of the approximation error, thereby reducing the perceptual error of the image.
alShaders is an open-source, production shader library for Arnold. In this document, we will examine what constitutes a production shader library and examine the design choices that shaped the form alShaders would take. As we will see, many of those choices follow naturally from the design of the renderer itself, so we will also take a brief look at the design of Arnold.
Alan King, Christopher Kulla, Alejandro Conty, Marcos Fajardo
A simple importance-sampling method for rendering subsurface light transport described by a BSSRDF on arbitrary geometry without any pre-computation.
Most axis-aligned bounding-box (AABB) based BVH-construction algorithms are numerically robust; however, BVH ray traversal algorithms for ray tracing are still susceptible to numerical precision errors. We show where these errors come from and how they can be efficiently avoided during traversal of BVHs that use AABBs.
Carlos Ureña, Marcos Fajardo, Alan King
We present an area-preserving parametrization for spherical rectangles which is an analytical function with domain in the unit rectangle and range in a region included in the unit-radius sphere. The parametrization preserves areas up to a constant factor and is thus very useful in the context of rendering as it allows to map random sample point sets in onto the spherical rectangle. This allows for easily incorporating stratified, quasi-Monte Carlo or other sampling strategies in algorithms that compute scattering from planar rectangular emitters.
Christopher Kulla, Marcos Fajardo
We introduce a set of robust importance sampling techniques which allow efficient calculation of direct and indirect lighting from arbitrary light sources in both homogeneous and heterogeneous media. We show how to distribute samples along a ray proportionally to the incoming radiance for point and area lights. In heterogeneous media, we decouple ray marching from light calculations by computing a representation of the transmittance function that can be quickly evaluated during sampling. This representation also allows the calculation of another probability density function which can direct samples to regions most likely to scatter light. [...]
Christopher Kulla, Marcos Fajardo
A method to effectively importance sample the single scattering integral in homogeneous participating media from point lights and area lights of arbitrary shapes.
Development of new advanced algorithms for digital production of photo-realistic synthesis images
The R&D project "IMAGINE", developed by Solid Angle, has been co-funded by the Ministry of Industry, Energy and Tourism within the National Plan of Scientific Investigation, Development and Technological Innovation 2013-2016 (File TSI-100600-2013-43)
2013 - 2015
Development of new advanced high performance algorithms applicable for digital content production.
The R&D project "NEWGENALGORYTHM", developed by Solid Angle, has been co-funded by the Ministry of Industry, Energy and Tourism within the National Plan of Scientific Investigation, Development and Technological Innovation 2013-2016 (File TSI-100600-2015-10)
2013 - 2016