華特迪士尼影業集團

In imaging, various tasks require a comparison of images between displays with different emission spectra. Even if the displays are calibrated and predicted to match using traditional colorimetry, individual differences in color perception of human observers can cause colors on two displays to appear mismatched. This phenomenon, known as observer metameric failure, can cause problems at different stages of content production when multiple decision makers have to approve the image. In this paper, a new Calibrated Observer Metameric Failure Index (COMFI) is proposed for use in such cases to predict the possibility of observer metameric failure. COMFI is designed to predict the amount of disagreement regarding the color match quality that can be expected from expert viewers evaluating colors on two displays with different spectra. It can help drive informed decisions about which displays cannot be compared in color critical tasks or which components to use during display design to minimize the risk of inducing observer metamerism. An experiment was conducted to estimate the amount of observer disagreement caused by observer metameric failure. Data from the experiment was used to drive the parameters of COMFI and to ensure its predictions relate closely to the real world experience.

A hallmark capability that defines a renderer as a production renderer is the ability to scale to handle scenes with extreme complexity, including complex illumination cast by a vast number of light sources. In this paper, we present Cache Points, the system used by Disney’s Hyperion Renderer to perform efficient unbiased importance sampling of direct illumination in scenes containing up to millions of light sources. Our cache points system includes a number of novel features. We build a spatial data structure over points that light sampling will occur from instead of over the lights themselves. We do online learning of occlusion and factor this into our importance sampling distribution. We also accelerate sampling in difficult volume scattering cases. Over the past decade, our cache points system has seen extensive production usage on every CG feature film and animated short produced by Walt Disney Animation Studios, enabling artists to design lighting environments without concern for complexity. In this paper, we will survey how the cache points system is built, works, impacts production lighting and artist workflows, and factors into the future of production rendering at Disney Animation.

Null-collision approaches for estimating transmittance and sampling free-flight distances are the current state-of-the-art for unbiased rendering of general heterogeneous participating media. However, null-collision approaches have a strict requirement for specifying a tightly bounding total extinction in order to remain both robust and performant; in practice this requirement restricts the use of null-collision techniques to only participating media where the density of the medium at every possible point in space is known a-priori. In production rendering, a common case is a medium in which density is defined by a black-box procedural function for which a bounding extinction cannot be determined beforehand. Typically in this case, a bounding extinction must be approximated by using an overly loose and therefore computationally inefficient conservative estimate. We present an analysis of how null-collision techniques degrade when a more aggressive initial guess for a bounding extinction underestimates the true maximum density and turns out to be non-bounding. We then build upon this analysis to arrive at two new techniques: first, a practical, efficient, consistent progressive algorithm that allows us to robustly adapt null-collision techniques for use with procedural media with unknown bounding extinctions, and second, a new importance sampling technique that improves ratio-tracking based on zero-variance sampling.

Sum-of-Squares Programming (SOSP) has recently been introduced to graphics as a unified way to address a large set of difficult problems involving higher order primitives. Unfortunately, a challenging aspect of this approach is the computational cost—especially for problems involving multiple geometries like collision detection. In this paper, we present techniques to reduce the cost of SOSP significantly. We use these improvements to speed up difficult problems like collision detection between Bézier triangles by as much as 300 ×. In addition, motivated by hair bundle simulation, we present SOSP based collision detection on the tapered cubic cylinder. We also present an algebraic formulation of rigid body motion enabling SOSP based collision detection for curved geometries and trajectories simultaneously. While these new formulations are complex, our speedups make them feasible. These advances improve the applicability of SOSP based collision detection and enable the continued progress of higher-order geometry processing.

We introduce a new volumetric sheen BRDF that approximates scattering observed in surfaces covered with normally-oriented fibers. Our previous sheen model was motivated by measured cloth reflectance, but lacked significant backward scattering. The model presented here allows a more realistic cloth appearance and can also approximate a dusty appearance. Our sheen model is implemented using a linearly transformed cosine (LTC) lobe fitted to a volumetric scattering layer. We detail the fitting process, and present and discuss our results.