Diffusion Based Photon Mapping

Density estimation employed in multi‐pass global illumination algorithms give cause to a trade‐off problem between bias and noise. The problem is seen most evident as blurring of strong illumination features. In particular, this blurring erodes fine structures and sharp lines prominent in caustics. To address this problem, we introduce a photon mapping algorithm based on nonlinear anisotropic diffusion. Our algorithm adapts according to the structure of the photon map such that smoothing occurs along edges and structures and not across. In this way, we preserve important illumination features, while eliminating noise. We demonstrate the applicability of our algorithm through a series of tests. In the tests, we evaluate the visual and computational performance of our algorithm comparing it to existing popular algorithms.     

Progressive Backward Photon Mapping

Programming and Computer Software - This work is devoted to the study of photon mapping methods applied to realistic rendering. In distinction from the conventional rendering methods, the...     

Interactive Global Photon Mapping

We present a photon mapping technique capable of computing high quality global illumination at interactive frame rates. By extending the concept of photon differentials to efficiently handle diffuse reflections, we generate footprints at all photon hit points. These enable illumination reconstruction by density estimation with variable kernel bandwidths without having to locate the k nearest photon hits first. Adapting an efficient BVH construction process for ray tracing acceleration, we build photon maps that enable the fast retrieval of all hits relevant to a shading point. We present a heuristic that automatically tunes the BVH build's termination criterion to the scene and illumination conditions. As all stages of the algorithm are highly parallelizable, we demonstrate an implementation using NVidia's CUDA manycore architecture running at interactive rates on a single GPU. Both light source and camera may be freely moved with global illumination fully recalculated in each frame.     

Efficient Caustic Rendering with Lightweight Photon Mapping

Robust and efficient rendering of complex lighting effects, such as caustics, remains a challenging task. While algorithms like vertex connection and merging can render such effects robustly, their significant overhead over a simple path tracer is not always justified and – as we show in this paper ‐ also not necessary. In current rendering solutions, caustics often require the user to enable a specialized algorithm, usually a photon mapper, and hand‐tune its parameters. But even with carefully chosen parameters, photon mapping may still trace many photons that the path tracer could sample well enough, or, even worse, that are not visible at all. Our goal is robust, yet lightweight, caustics rendering. To that end, we propose a technique to identify and focus computation on the photon paths that offer significant variance reduction over samples from a path tracer. We apply this technique in a rendering solution combining path tracing and photon mapping. The photon emission is automatically guided towards regions where the photons are useful, i.e., provide substantial variance reduction for the currently rendered image. Our method achieves better photon densities with fewer light paths (and thus photons) than emission guiding approaches based on visual importance. In addition, we automatically determine an appropriate number of photons for a given scene, and the algorithm gracefully degenerates to pure path tracing for scenes that do not benefit from photon mapping.     

Coherent Photon Mapping on the Intel MIC Architecture

Photon mapping is a global illumination algorithm which is composed of two steps: photon tracing and photon searching. During photon searching step, each shading point needs to search the photon-tree t...     

The Beam Radiance Estimate for Volumetric Photon Mapping

We present a new method for efficiently simulating the scattering of light within participating media. Using a theoretical reformulation of volumetric photon mapping, we develop a novel photon gathering technique for participating media. Traditional volumetric photon mapping samples the in‐scattered radiance at numerous points along the length of a single ray by performing costly range queries within the photon map. Our technique replaces these multiple point‐queries with a single beam‐query, which explicitly gathers all photons along the length of an entire ray. These photons are used to estimate the accumulated in‐scattered radiance arriving from a particular direction and need to be gathered only once per ray. Our method handles both fixed and adaptive kernels, is faster than regular volumetric photon mapping, and produces images with less noise.     

Hierarchical SLAM: Real-Time Accurate Mapping of Large Environments

In this paper, we present a hierarchical mapping method that allows us to obtain accurate metric maps of large environments in real time. The lower (or local) map level is composed of a set of local maps that are guaranteed to be statistically independent. The upper (or global) level is an adjacency graph whose arcs are labeled with the relative location between local maps. An estimation of these relative locations is maintained at this level in a relative stochastic map. We propose a close to optimal loop closing method that, while maintaining independence at the local level, imposes consistency at the global level at a computational cost that is linear with the size of the loop. Experimental results demonstrate the efficiency and precision of the proposed method by mapping the Ada Byron building at our campus. We also analyze, using simulations, the precision and convergence of our method for larger loops.     

Hierarchical relaxation

In this paper we discuss a hierarchical relaxation method for solving a system of equations. The method proceeds by adjoining to a given system of equations whose solution is sought, an auxiliary hierarchy of systems. The relaxation procedure consists of a judicious mixing of relaxation steps in the different members of the hierarchy. When the choice of the hierarchy and the mixing of relaxation steps are appropriate, the entire procedure provides an acceleration of the relaxation process toward a determination of the solution of the original system. The procedure lends itself to parallel implementation, even in an asynchronous mode. We discuss these aspects of hierarchical relaxation as well.     

Hierarchical textures

Rich, interesting patterns create an oasis of aesthetic pleasure between the arid lands of complete randomness and complete order. In addition to their inherent beauty, patterns prove useful in graphics when we use them as textures. Textures were originally used to add color detail to shapes. Today, textures control everything from shape details to the placement of extras in digital crowd scenes. Though not appropriate for everything, such patterns can be used for applications from ornamentation to creating complex 3D structures and motion. One easy and powerful way to create rich textures is to start with something simple, and then use that seed along with some rules to “grow” something more complicated. Lots of growing schemes produce both repeating and non-repeating patterns. One of the simplest techniques is called “tiling”, where you place down multiple copies of a single starting shape, or tile, according to some (usually simple) rules. You can create rich tilings in surprisingly many ways. I look at a tiling technique based on using a set of simple symmetry operations     

Hierarchical Estimator

In this paper, a new machine learning solution for function approximation is presented. It combines many simple and relatively inaccurate estimators to achieve high accuracy. It creates – in incremental manner – hierarchical, tree-like structure, adapting it to the specific problem being solved. As most variants use the errors of already constructed parts to direct further construction, it may be viewed as example of boosting – as understood in general sense. The influence of particular constituent estimator on the whole solution’s output is not constant, but depends on the feature vector being evaluated.Provided in this paper are: general form of the metaalgorithm, a few specific, detailed solutions, theoretical basis and experimental results with one week power load prediction for country-wide power distribution grid and on simple test datasets.     

Hierarchical monitors

A technique is presented for constructing an operating system as a hierarchical set of monitors. The hierarchy reflects and reinforces the system structure, and extends down to the system nucleus itself. The nucleus is in fact treated as a specialized monitor for handling the central processor. The technique has been used to write a small pilot system for a DEC PDP-15, and experience with the system is reported. The mutual exclusion problem for monitor procedures is discussed, and a viable solution suggested.     

Hierarchical constraints

Constrained clustering received a lot of attention in the last years. However, the widely used pairwise constraints are not generally applicable for hierarchical clustering, where the goal is to derive a cluster hierarchy instead of a flat partition. Therefore, we propose for the hierarchical setting—based on the ideas of pairwise constraints—the use of must-link-before (MLB) constraints. In this paper, we discuss their properties and present an algorithm that is able to create a hierarchy by considering these constraints directly. Furthermore, we propose an efficient data structure for its implementation and evaluate its effectiveness with different datasets in a text clustering scenario.     

Hierarchical deduction

This paper describes an hierarchical deduction proof procedure. This procedure proves a theorem by searching for a proof acceptable to an hierarchical deduction structire; those derivations which are irrelevant to this proof are limited by means of a set of completeness-preserving refinements of the basic procedure, such as constraints on framed literals and on common tails, a proper reduction refinement, a global subsumption constraint, and a level subgoal reordering refinement, etc. In addition to this basic algorithm, we will present a partial set of support strategy and a semantically guided hierarchical deduction for the incorporation of semantics and human factors. The paper concludes with proofs concerning the completeness of the basic algorithm and the results of a computer implementation applied to some nontrivial problems.This work was supported in part by NSF grant MCS-8313499.     

Hierarchical fuzzy control

In a conventional rule based fuzzy control system, the rules are of the following form: if (condition) then (action), and all rules are essentially in a random order. The number of rules increases exponentially as the number of the system variables, on which the fuzzy rules are based, is increased. In this paper, the rules are structured in a hierarchical way so that the total number of rules will be a linear function of the system variables. The hierarchical fuzzy control algorithm developed in this paper is applied to control the feedwater flow to a steam generator of a power plant. The simulation results show that the hierarchical fuzzy controller yields superior performance over the conventional PID controller.     

Hierarchical Layout Verification

This article presents a hierarchical cell structure that has been Used successfully to improve the performance of Intel's connectivity verifier and design rule checker. A unique algorithm for performing design rule checks efficiently in a hierarchical environment is discussed in detail. To undersize and oversize in a hierarchical environment without disrupting the cell structure, the definition of sizing must be changed so that geometries inside a cell and touching the cell boundaries do not pull away and geometries outside the cell do not extend inside. There are also a few Pathologies?caused mostly by looking at only a small portion of the layout, outside of the context where it is used. Nevertheless, careful use of hierarchical design can deliver order-of-magnitude improvements in layout checking runtime.     

Hierarchical image fusion

A hierarchical image fusion scheme is presented that preserves those details from the input images that are most relevant to visual perception. Results show that fused images present a more detailed representation of the scene and provide information that cannot be obtained by viewing the input images separately. Detection, recognition, and search tasks may therefore benefit from this fused image representation.