Generalized Image Acquisition and Analysis

An evaluation of optical flow algorithms for background oriented schlieren imaging

The background oriented schlieren method (BOS) allows for accurate flow measurements with a simple experimental configuration. To estimate per-pixel displacement vectors between two images, BOS systems traditionally borrow window-based algorithms from particle image velocimetry. In this paper, we evaluate the performance of more recent optical flow methods in BOS settings. We also analyze the impact of different background patterns, suggesting the use of a pattern with detail at many scales. Experiments with both synthetic and real datasets show that the performance of BOS systems can be significantly improved through a combination of optical flow algorithms and multiscale background.

Projects

From Capture to Simulation - Connecting Forward and Inverse Problems in Fluids

James Gregson, Ivo Ihrke, Nils Thuerey, Wolfgang Heidrich
SIGGRAPH 2014



Abstract

We explore the connection between fluid capture, simulation and proximal methods, a class of algorithms commonly used for inverse problems in image processing and computer vision. Our key finding is that the proximal operator constraining fluid velocities to be divergence-free is directly equivalent to the pressure-projection methods commonly used in incompressible flow solvers. This observation lets us treat the inverse problem of fluid tracking as a constrained flow problem all while working in an efficient, modular framework. In addition it lets us tightly couple fluid simulation into flow tracking, providing a global prior that significantly increases tracking accuracy and temporal coherence as compared to previous techniques. We demonstrate how we can use these improved results for a variety of applications, such as re-simulation, detail enhancement, and domain modification. We furthermore give an outlook of the applications beyond fluid tracking that our proximal operator framework could enable by exploring the connection of deblurring and fluid guiding.
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Bibtex

@article{Gregson:14,
author = {James Gregson and Ivo Ihrke and Nils Thuerey and Wolfgang Heidrich},
title = {From Capture to Simulation - Connecting Forward and Inverse Problems in Fluids},
journal = {ACM Trans. on Graphics (SIGGRAPH'14)},
volume = 33, number = 4, year = 2014,
pages = {xx--yy},
}
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