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Ben Spencer, BSc (Wales)
PhD Student
Research Interests: Global illumination. Classical ray tracing and rendering. Image processing. Visualisation.
Supervisor: Dr. Mark W. Jones
Address:
Room 402
Department of Computer Science
Swansea University
Singleton Park
Swansea
SA2 8PP
E-mail:
csbenjamin at swansea dot ac dot uk
Links:
www.igneus.co.uk - Research homepage
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Into the Blue: Better Caustics Through Photon Relaxation
B. Spencer, M. W. Jones
To appear at Eurographics 2009
The photon mapping method is one of the most popular algorithms employed in computer graphics today. However, obtaining good results is dependent on several variables including kernel shape and bandwidth, as well as the properties of the initial photon distribution. While the photon density estimation problem has been the target of extensive research, most algorithms focus on new methods of optimising the kernel to minimise noise and bias. In this paper we break from convention and propose a new approach that directly redistributes the underlying photons. We show that by relaxing the initial distribution into one with a blue noise spectral signature we can dramatically reduce background noise, particularly in areas of uniform illumination. In addition, we propose an efficient heuristic to detect and preserve features and discontinuities. We then go on to demonstrate how reconfiguration also permits the use of very low bandwidth kernels, greatly improving render times whilst reducing bias.
| NEW: Making-of winning Computer Graphics Forum 2009 cover competition image (left) |
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Evenly-Spaced Streamlines for Surfaces: An Image-Based Approach
B. Spencer, R.S. Laramee, E. Zhang, G. Chen
To appear in Computer Graphics Forum
We introduce a novel, automatic streamline seeding algorithm for vector fields defined on surfaces in 3D space. The algorithm generates evenly-spaced streamlines fast, simply, and efficiently for any general surface-based vector field. It is general because it handles large, complex, unstructured, adaptive resolution grids with holes and discontinuities, does not require a parameterisation, and can generate both sparse and dense representations of the flow. It is efficient because streamlines are only integrated for visible portions of the surface. It is simple because the image-based approach removes the need to perform streamline tracing on a triangular mesh, a process which is complicated at best. And it is fast because it makes effective, balanced use of both the CPU and the GPU. The key to the algorithm’s speed, simplicity, and efficiency is its image-based seeding strategy. We demonstrate our algorithm on complex, real-world simulation data sets from computational fluid dynamics and compare it with a object-space streamline visualisations.
• PDF (Pre-print. 15.2MB)
• Movie (35.9MB)
• BibTex (available soon)
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Hierarchical Photon Mapping
B. Spencer and M. W. Jones
IEEE Transactions on Visualization and Computer Graphics, 15(1), 49-61, Jan/Feb 2009.
Photon mapping is an efficient method for producing high-quality, photorealistic images with full global illumination. In this paper we present a more accurate and efficient approach to final gathering using the photon map based upon hierarchical evaluation of the photons over each surface. We use the footprint of each gather ray to calculate the irradiance estimate area rather than deriving it from the local photon density. We then describe an efficient method for computing the irradiance from the photon map given an arbitrary estimate area. Finally, we demonstrate how the technique may be used to reduce variance and increase efficiency when sampling diffuse and glossy-specular BRDFs.