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23
Global Illumination using Photon Maps
, 1996
"... This paper presents a two pass global illumination method based on the concept of photon maps. It represents a significant improvement of a previously described approach both with respect to speed, accuracy and versatility. In the first pass two photon maps are created by emitting packets of energy ..."
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Cited by 217 (9 self)
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This paper presents a two pass global illumination method based on the concept of photon maps. It represents a significant improvement of a previously described approach both with respect to speed, accuracy and versatility. In the first pass two photon maps are created by emitting packets of energy (photons) from the light sources and storing these as they hit surfaces within the scene. We use one high resolution caustics photon map to render caustics that are visualized directly and one low resolution photon map that is used during the rendering step. The scene is rendered using a distribution ray tracing algorithm optimized by using the information in the photon maps. Shadow photons are used to render shadows more efficiently and the directional information in the photon map is used to generate optimized sampling directions and to limit the recursion in the distribution ray tracer by providing an estimate of the radiance on all surfaces with the exception of specular...
A general imaging model and a method for finding its parameters
 In Proc. ICCV
, 2001
"... Linear perspective projection has served as the dominant imaging model in computer vision. Recent developments in image sensing make the perspective model highly restrictive. This paper presents a general imaging model that can be used to represent an arbitrary imaging system. It is observed that al ..."
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Cited by 95 (2 self)
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Linear perspective projection has served as the dominant imaging model in computer vision. Recent developments in image sensing make the perspective model highly restrictive. This paper presents a general imaging model that can be used to represent an arbitrary imaging system. It is observed that all imaging systems perform a mapping from incoming scene rays to photosensitive elements on the image detector: This mapping can be conveniently described using a set of virtual sensing elements called raxels. Raxels include geometric, radiometric and optical properties. We present a novel calibration method that uses structured light patterns to extract the raxel parameters of an arbitrary imaging system. Experimental results for perspective as well as nonperspective imaging systems are included. 1
RealTime Caustics
, 2003
"... We present a new algorithm to render caustics. The algorithm discretizes the specular surfaces into sample points. Each of the sample points is treated as a pinhole camera that projects an image of the incoming light onto the diffuse receiver surfaces. Antialiasing is performed by considering the ..."
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Cited by 30 (0 self)
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We present a new algorithm to render caustics. The algorithm discretizes the specular surfaces into sample points. Each of the sample points is treated as a pinhole camera that projects an image of the incoming light onto the diffuse receiver surfaces. Antialiasing is performed by considering the local surface curvature at the sample points to filter the projected images. The algorithm can be implemented using programmable texture mapping hardware. It allows to render caustics in fully dynamic scenes in realtime on current PC hardware.
OpenRT  A Flexible and Scalable Rendering Engine for Interactive 3D Graphics
, 2002
"... Figure 1: Examples of interactively rendering complex and dynamic scenes with a raytracingbased renderer. The scenes show a prelighted theatre, robots moving through a city, large numbers of moving trees with sharp shadows, as well as the integration of volumes, lightfields, and procedural shadin ..."
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Cited by 23 (11 self)
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Figure 1: Examples of interactively rendering complex and dynamic scenes with a raytracingbased renderer. The scenes show a prelighted theatre, robots moving through a city, large numbers of moving trees with sharp shadows, as well as the integration of volumes, lightfields, and procedural shading in an office environment. These examples run interactively at a resolution of 640 × 480 using four to eight dual PCs. Raytracing is wellknown as a general and flexible rendering algorithm that generates highquality images. But in the past, raytracing implementations were too slow to be used in an interactive context. Recently, the performance of raytracing has been increased by over an order of magnitude, making it interesting as an alternative to rasterizationbased rendering. We present a new rendering engine for interactive 3D graphics based on a fast, scalable, and distributed raytracer. It offers an extended OpenGLlike API, supports interactive modifications of the scene, handles complex scenes with millions of polygons, and scales efficiently to many client machines. We demonstrate that the new renderer provides more flexibility, more rendering features, and higher performance for complex scenes than current rasterization hardware. Its flexibility enables new types of applications including a system for interactive global illumination.
Efficient Importance Sampling Techniques for the Photon Map
, 2000
"... In global illumination computations the photon map is a powerful tool for approximating the irradiance, which is stored independent from scene geometry. By presenting a new algorithm, which uses novel importance sampling techniques, we improve the memory footprint of the photon map, simplify the cau ..."
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Cited by 19 (4 self)
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In global illumination computations the photon map is a powerful tool for approximating the irradiance, which is stored independent from scene geometry. By presenting a new algorithm, which uses novel importance sampling techniques, we improve the memory footprint of the photon map, simplify the caustic generation, and allow for a much faster sampling of direct illumination in complicated models as they arise in a production environment.
Density Control for Photon Maps
 In Rendering Techniques 2000: 11th Eurographics Workshop on Rendering
, 2000
"... The photon map method allows efficient computation of global illumination in general scenes. Individual photon hits, generated using Monte Carlo particle tracing, are stored in the maps and form a geometry independent representation of the illumination. Two important issues with the photon map ar ..."
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Cited by 18 (0 self)
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The photon map method allows efficient computation of global illumination in general scenes. Individual photon hits, generated using Monte Carlo particle tracing, are stored in the maps and form a geometry independent representation of the illumination. Two important issues with the photon map are memory requirements to store the photons and the question how many photons are needed for an accurate representation of illumination in a certain scene. In this paper we introduce a method to control the density of photon maps by storing photons selectively based on a local required density criterion. This reduces memory usage significantly since in unimportant or overdense regions less photons are stored. Results for caustic photon maps and global photon maps representing full illumination show a decrease in number of photons of a factor of 2 to 5. The required density states how accurate the photon map should be at a certain location and determines how many photons are needed in total. We also derive such a criterion based on a novel pathimportancebased first pass, taking some steps towards solving the difficult 'how many photons' question.
The Raxel Imaging Model and RayBased Calibration
, 2005
"... An imaging model provides a mathematical description of correspondence between points in a scene and in an image. The dominant imaging model, perspective projection, has long been used to describe traditional cameras as well as the human eye. We propose an imaging model which is flexible enough to r ..."
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Cited by 18 (3 self)
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An imaging model provides a mathematical description of correspondence between points in a scene and in an image. The dominant imaging model, perspective projection, has long been used to describe traditional cameras as well as the human eye. We propose an imaging model which is flexible enough to represent an arbitrary imaging system. For example using this model we can describe systems using fisheye lenses or compound insect eyes, which violate the assumptions of perspective projection. By relaxing the requirements of perspective projection, we give imaging system designers greater freedom to explore systems which meet other requirements such as compact size and wide field of view. We formulate our model by noting that all imaging systems perform a mapping from incoming scene rays to photosensitive elements on the image detector. This mapping can be conveniently described using a set of virtual sensing elements called raxels. Raxels include geometric, radiometric and optical properties. We present a novel ray based calibration method that uses structured light patterns to extract the raxel parameters of an arbitrary imaging system. Experimental results for perspective as well as nonperspective imaging systems are included.
Interactive ScreenSpace Accurate Photon Tracing on GPUs
 EUROGRAPHICS SYMPOSIUM ON RENDERING, TOMAS AKENINEMÖLLER AND WOLFGANG HEIDRICH (EDITORS)
, 2006
"... Recent advances in algorithms and graphics hardware have opened the possibility to render caustics at interactive rates on commodity PCs. This paper extends on this work in that it presents a new method to directly render caustics on complex objects, to compute one or several refractions at such obj ..."
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Cited by 16 (2 self)
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Recent advances in algorithms and graphics hardware have opened the possibility to render caustics at interactive rates on commodity PCs. This paper extends on this work in that it presents a new method to directly render caustics on complex objects, to compute one or several refractions at such objects and to simulate caustics shadowing. At the core of our method is the idea to avoid the construction of photon maps by tracing photons in screenspace on programmable graphics hardware. Our algorithm is based on the rasterization of photon paths into texture maps. Intersection events are then resolved on a perfragment basis using layered depth images. To correctly spread photon energy in screenspace we render aligned point sprites at the diffuse receivers where photons terminate. As our method does neither require any preprocessing nor an intermediate radiance representation it can efficiently deal with dynamic scenery and scenery that is modified, or even created on the GPU.
Simulating the Flow of Liquid Droplets
, 1998
"... The everchanging nature of liquids makes them very difficult to model and animate. This paper addresses the simulation of one aspect of liquids, i.e. droplets running down surfaces. We present a model oriented towards a visuallysatisfying simulation and efficiency. The efficiency results ..."
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Cited by 12 (0 self)
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The everchanging nature of liquids makes them very difficult to model and animate. This paper addresses the simulation of one aspect of liquids, i.e. droplets running down surfaces. We present a model oriented towards a visuallysatisfying simulation and efficiency. The efficiency results
Balancing Considered Harmful  Faster Photon Mapping using the Voxel Volume Heuristic 
 Computer Graphics Forum
, 2004
"... Photon mapping is one of the most important algorithms for computing global illumination. Especially for efficiently producing convincing caustics, there are no real alternatives to photon mapping. On the other hand, photon mapping is also quite costly: Each radiance lookup requires to find the k ne ..."
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Cited by 11 (1 self)
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Photon mapping is one of the most important algorithms for computing global illumination. Especially for efficiently producing convincing caustics, there are no real alternatives to photon mapping. On the other hand, photon mapping is also quite costly: Each radiance lookup requires to find the k nearest neighbors in a kdtree, which can be more costly than shooting several rays. Therefore, the nearestneighbor queries often dominate the rendering time of a photon map based renderer. In this paper, we present a method that reorganizes  i.e. unbalances  the kdtree for storing the photons in a way that allows for finding the knearest neighbors much more efficiently, thereby accelerating the radiance estimates by a factor of 1.23.4. Most importantly, our method still finds exactly the same knearestneighbors as the original method, without introducing any approximations or loss of accuracy. The impact of our method is demonstrated with several practical examples.