Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Werner Purgathofer is active.

Publication


Featured researches published by Werner Purgathofer.


eurographics symposium on rendering techniques | 1995

The Stochastic Ray Method for Radiosity

László Neumann; Werner Purgathofer; Robert F. Tobler; Attila Neumann; Pavol Eliás; Martin Feda; Xavier Pueyo

This paper solves the system of radiosity equations with a stochastic numerical approach. Due to the high complexity of the problem for highly complex scenes, a stochastic variation of Jacobi iteration is developed which converges stochastically to the correct solution. The new method, called the Stochastic Ray Method, is a significant improvement of Stochastic Radiosity. A large number of independent rays is chosen stochastically by importance sampling of the patches according to their power after the previous iteration step. They all carry an equal amount of power into random directions, thereby representing together the total energy interreflection of the entire environment in a stochastic manner. Assuming a correctly distributed initial solution, which can be reached easily, the iteration process converges quickly and reduces the error in the result faster than other stochastic radiosity approaches. The new algorithm can easily be extended to treat various phenomena which are normally rather costly to incorporate in radiosity environments, perfect specular reflection and specular transmittance, non-diffuse self-emission and point light sources.


international conference on image processing | 1994

Forced random dithering: improved threshold matrices for ordered dithering

Werner Purgathofer; Robert F. Tobler; Manfred Geiler

This paper examines the possibilities of improving halftoning techniques using dispersed dots. This corresponds to finding micro-dot distributions that approximate the intensity levels that have to be rendered. A widely used halftoning method is ordered dithering, which uses a threshold matrix to decide if a micro-dot should be set in the output image. A way to generate improved threshold matrices for ordered dithering will be introduced that avoids unwanted low-frequency portions without introducing too much random noise into the rendered image. Since the presented method produces images of high quality it is ideally suited for output generation in high-end image processing systems.<<ETX>>


Archive | 1995

A New Stochastic Radiosity Method for Highly Complex Scenes

László Neumann; Martin Feda; Manfred Kopp; Werner Purgathofer

This paper presents a linear-time radiosity algorithm for very complex environments. The new algorithm is based on a progressive refinement iteration process with stochastic instead of deterministic convergence. Each iteration step simulates one interreflection step for all patches similar to Jacobi iteration, but with an approximate interreflection matrix rather than with the exact one. The stochastic shooting method is described, which computes such approximate interreflection matrices at very low computational cost. The efficiency of the algorithm can be further increased by several variance reduction methods.


Archive | 1992

Fast Radiosity by Parallelization

Werner Purgathofer; Michael Zeiller

A parallel solution of the radiosity approach for realistic image rendering is presented. The tremendous costs of computation power and memory of radiosity implementations are met by parallelization on a computer architecture based on transputers. Form-factors are computed in parallel and independently on several processors, thus giving a high acceleration of this most computationally intensive task. Parallel solutions for equation solving and rendering are also introduced. These parallelizations of the radiosity approach leed to an extraordinary speed-up in image generation and can be adapted for different kinds of parallel computer architectures.


eurographics symposium on rendering techniques | 1996

Importance-driven stochastic ray radiosity

Attila Neumann; László Neumann; Philippe Bekaert; Yves D. Willems; Werner Purgathofer

The stochastic ray radiosity method [10] is a radiosity method in which no form-factors are computed explicitly. Because of this, the method is very well-suited to compute the radiance distribution in very complex diffuse environments. In this paper we present an extension of this method which will provide a significant reduction of computational cost in cases where accurate knowledge of the illumination is needed in only a small part of the scene. This is accomplished by computing a second quantity, called importance, during the radiance computation. Importance is then used to modulate the patch sampling probabilities in order to obtain lower variance in relevant regions of the scene.


international conference on image processing | 1994

A comparison of techniques for the transformation of radiosity values to monitor colors

Peter Ferschin; Ingeborg Tastl; Werner Purgathofer

In the rendering process of radiosity scenes, the computed radiosity values have to be converted to color values that can be displayed on a CRT monitor. Usually radiosity calculations as well as various color calculations are performed in the RGB color space. Unfortunately the radiosity values can be outside a monitor gamut, which is a three-dimensional solid surrounding the set of all displayable colors for that device. The radiosity approach can be used either for rendering images with global illumination effects or for accurate physical simulation of light propagation. This paper introduces several techniques to transform radiosity values to monitor colors. These techniques use either clipping or compression, either scene dependent or independent algorithms and work either in the RGB, CIELUV or CIELAB color space. A simple, yet visually appealing, nonlinear color compression technique is introduced to generate smooth intensity gradients on a CRT monitor. The problems of accurate perceptual display of radiosity scenes are discussed as well as some new ideas from color theory are presented that might be helpful for a solution of this task.<<ETX>>


Archive | 1994

Color Spaces and Human Color Perception

Ingeborg Tastl; Werner Purgathofer

This paper is concerned about the definition and features of color spaces in general, about the differences between geometrical and perceptual color spaces and about one possible way to create a colorimetrie system, which is more based on human color perception than color spaces commonly used in computer graphics.


Computer Graphics Forum | 1994

A Median Cut Algorithm for Efficient Sampling of Radiosity Functions

Martin Feda; Werner Purgathofer

This paper presents an efficient method for sampling the illumination functions in higher order radiosity algorithms. In such algorithms, the illumination function is not assumed to be constant across each patch, but it is approximated by a function which is at least C1 continuous. Our median cut sampling algorithm is inspired by the observation that many form factors are computed at higher precision than is necessary. While a high sampling rate is necessary in regions of high illumination, dark areas can be sampled at a much lower rate to compute the received radiosity within a given precision. We adaptively subdivide the emitter into regions of approximately equal influence on the result. Form factors are evaluated by the disk approximation and a ray tracing based test for occlusion detection. The implementation of a higher order radiosity system using B‐splines as radiosity function is described. The median cut algorithm can also be used for radiosity algorithms based on the constant radiosity assumption.


Archive | 1995

Efficient Collision Detection for General CSG Objects

Michael Zeiller; Werner Purgathofer; Michael Gervautz

A complete method to detect collisions among objects modeled with constructive solid geometry within a computer animation system is introduced. In contrast to existing methods the CSG objects may be constructed from arbitrary kinds of primitives, e.g., polyhedral primitives or primitives with curved surfaces. Collision detection is performed in three stages. Bounding volumes and spatial subdivision are used to reduce the complexity of the CSG objects for detailed analysis. In those regions that are partially covered by both objects an exact collision test for those small parts of the CSG objects that are inside the region is performed. To be able to deal with general CSG objects an adaptive collision detection algorithm for CSG objects containing curved primitives is presented.


Displays | 1993

An interactive tool for the visualization of cathode-ray tube monitor gamuts

Ingeborg Tastl; Werner Purgathofer

Abstract The aim of this work was the development of an interactive tool for the visualization and the comparison of cathode-ray tube monitor gamuts.

Collaboration


Dive into the Werner Purgathofer's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Attila Neumann

Vienna University of Technology

View shared research outputs
Top Co-Authors

Avatar

Helwig Löffelmann

Vienna University of Technology

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge