Enhancement of synthetic schlieren image resolution using total variation optical flow: application to thermal experiments in a Hele-Shaw cell

Letelier, Juvenal A.; Herrera, Paulo; Mujica, Nicolás; Ortega, Juan‐Pablo

doi:10.1007/s00348-015-2109-1

Cited by 16 publications

(13 citation statements)

References 48 publications

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“…Smith et al [62] found the Horn-Schunck algorithm to yield robust, higher-quality flow results quicker than correlation processing when applied to wind tunnel and flight-test BOS data. Letelier et al [63] demonstrated improved BOS resolution using a total variation optical flow approach applied to thermal convection in a Hele-Shaw cell. For processing PIV image pairs, Liu et al [64] found improved accuracy and much better resolution using optical flow, provided the parameters of the computation are properly selected and there are no significant illumination changes between frames.…”

Section: Bos Softwarementioning

confidence: 99%

A review of recent developments in schlieren and shadowgraph techniques

Settles¹,

Hargather

2017

Meas. Sci. Technol.

315

154

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Schlieren and shadowgraph techniques are used around the world for imaging and measuring phenomena in transparent media. These optical methods originated long ago in parallel with telescopes and microscopes, and although it might seem that little new could be expected of them on the timescale of 15 years, in fact several important things have happened that are reviewed here. The digital revolution has had a transformative effect, replacing clumsy photographic film methods with excellent-though expensive-high-speed video cameras, making digital correlation and processing of shadow and schlieren images routine, and providing an entirely-new synthetic schlieren technique that has attracted a lot of attention: background-oriented schlieren or BOS. Several aspects of modern schlieren and shadowgraphy depend upon laptop-scale computer processing of images using an imagecapable language such as MATLAB ™. BOS, shock-wave tracking, schlieren velocimetry, synthetic streak-schlieren, and straightforward quantitative density measurements in 2D flows are all recent developments empowered by this digital and computational capability.

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Section: Bos Softwarementioning

confidence: 99%

A review of recent developments in schlieren and shadowgraph techniques

Settles¹,

Hargather

2017

Meas. Sci. Technol.

315

154

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“…Finally, Fig. 2(c) shows the displacement field obtained after transforming the filtered signals back to the spatial domain, applying equations (7) and (8) and solving for u(r). As demonstrated in Figs.…”

Section: Fourier Demodulation Of Arbitrary 2d Periodic Patternsmentioning

confidence: 99%

“…Over the last few decades, with the advent of high-resolution digital cameras and cheaply available computing power, synthetic Schlieren imaging (SSI) [1,2], also known as background-oriented Schlieren (BOS) [3], has proven to be a versatile tool for the full-field measurement of optical inhomogeneities (Schlieren) in transparent media [4,5,6,7,8,9]. The optical setup, proposed well before the digital era [10,11], is extremely simple and low-cost, requiring only a digital camera and a suitable backdrop (see Fig.…”

Section: Introductionmentioning

confidence: 99%

Real-time quantitative Schlieren imaging by fast Fourier demodulation of a checkered backdrop

Wildeman

2018

Exp Fluids

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A quantitative synthetic Schlieren imaging (SSI) method based on fast Fourier demodulation is presented. Instead of a random dot pattern (as usually employed in SSI), a 2D periodic pattern (such as a checkerboard) is used as a backdrop to the refractive object of interest. The range of validity and accuracy of this "Fast Checkerboard Demodulation" (FCD) method are assessed using both synthetic data and experimental recordings of patterns optically distorted by small waves on a water surface. It is found that the FCD method is at least as accurate as sophisticated, multi-stage, digital image correlation (DIC) or optical flow (OF) techniques used with random dot patterns, and it is significantly faster. Efficient, fully vectorized, implementations of both the FCD and DIC/OF schemes developed for this study are made available as open source Matlab scripts.

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“…Various modifications of Schlieren techniques [1][2][3] have been used for flow visualization over a hundred year. With the rise of digital sensing technology, Background Oriented Schlieren (BOS) techniques are emerging [4][5][6]. BOS is an optical flow diagnostic technique used to measure density gradients in a flow field by tracking the apparent distortion of a target dot pattern.…”

Section: Introductionmentioning

confidence: 99%

Quantitative Schlieren imaging based on fringe projection

Psota

Stašík²,

Kredba³

et al. 2022

EPJ Web Conf.

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An effective yet simple quantitative synthetic Schlieren imaging technique is presented in this paper. A multiplexed fringe pattern displayed on a common laptop screen is observed through a disturbed medium resulting in a change of the fringe pattern. Fourier analysis of such pattern provides high-resolution and almost real time measurement of rays’ deflection due to the medium refractive index variation. The developed technique was applied for measurement of a compressible fluid discharge from a narrow channel in a wind tunnel.

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Enhancement of synthetic schlieren image resolution using total variation optical flow: application to thermal experiments in a Hele-Shaw cell

Cited by 16 publications

References 48 publications

A review of recent developments in schlieren and shadowgraph techniques

A review of recent developments in schlieren and shadowgraph techniques

Real-time quantitative Schlieren imaging by fast Fourier demodulation of a checkered backdrop

Quantitative Schlieren imaging based on fringe projection

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