Generalized Image Acquisition and Analysis

Time-resolved 3D Capture of Non-stationary Gas Flows

Fluid simulation is one of the most active research areas in computer graphics. However, it remains difficult to obtain measurements of real fluid flows for validation of the simulated data. In this paper, we take a step in the direction of capturing flow data for such purposes. Specifically, we present the first time-resolved Schlieren tomography system for capturing full 3D, non-stationary gas flows on a dense volumetric grid. Schlieren tomography uses 2D ray deflection measurements to reconstruct a time-varying grid of 3D refractive index values, which directly correspond to physical properties of the flow. We derive a new solution for this reconstruction problem that lends itself to efficient algorithms to robustly work with relatively small numbers of cameras. Our physical system is easy to set up, and consists of an array of relatively low cost rolling-shutter camcorders that are synchronized with a new approach. We demonstrate our method with real measurements, and analyze precision with synthetic data for which ground truth information is available.

Projects

Acquisition and Analysis of Bispectral Bidirectional Reflectance and Reradiation Distribution Functions

Matthias Hullin, Johannes Hanika, Boris Ajdin, Hans-Peter Seidel, Jan Kautz, Hendrik P. A. Lensch
In: Proceedings of SIGGRAPH 2010.



Abstract

In fluorescent materials, light from a certain band of incident wavelengths is reradiated at longer wavelengths, i.e., with a reduced per-photon energy. While fluorescent materials are common in everyday life, they have received little attention in computer graphics. Especially, no bidirectional reradiation measurements of fluorescent materials have been available so far. In this paper, we extend the well-known concept of the bidirectional reflectance distribution function (BRDF) to account for energy transfer between wavelengths, resulting in a Bispectral Bidirectional Reflectance and Reradiation Distribution Function (bispectral BRRDF). Using a bidirectional and bispectral measurement setup, we acquire reflectance and reradiation data of a variety of fluorescent materials, including vehicle paints, paper and fabric, and compare their renderings with RGB, RGB×RGB, and spectral BRDFs. Our acquisition is guided by a principal component analysis on complete bispectral data taken under a sparse set of angles. We show that in order to faithfully reproduce the full bispectral information for all other angles, only a very small number of wavelength pairs needs to be measured at a high angular resolution.

Bibtex

@article{hullin2010acquisition,
title={{Acquisition and analysis of bispectral bidirectional reflectance and reradiation distribution functions}},
author={Hullin, M.B. and Hanika, J. and Ajdin, B. and Seidel, H.P. and Kautz, J. and Lensch, H.},
journal={ACM Transactions on Graphics (TOG)},
volume={29},
number={4},
pages={1--7},
issn={0730-0301},
year={2010},
publisher={ACM}
}
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