Real-time quantitative Schlieren imaging by fast Fourier demodulation of a checkered backdrop
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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.
I am indebted to Antonin Eddi and Emmanuel Fort for their enthusiastic support during the development of the FCD method in their groups. I would also like to thank Guillaume Du Moulinet d’Hardemare and Lucie Domino for testing the method in their experiments and giving the necessary practical feedback.
- Brox T, Bruhn A, Papenberg N, Weickert J (2004) High accuracy optical flow estimation based on a theory for warping. In: Pajdla T, Matas J (eds) Computer Vision—ECCV 2004: 8th European Conference on Computer Vision, Prague, Czech Republic, May 11–14, 2004. Proceedings, Part IV. Springer, Berlin, Heidelberg, pp 25–36. https://doi.org/10.1007/978-3-540-24673-2-3
- Harker M, O’Leary P (2011) Least squares surface reconstruction from gradients: direct algebraic methods with spectral, Tikhonov, and constrained regularization. In: CVPR 2011 (IEEE, 2011), pp 2529–2536. https://doi.org/10.1109/CVPR.2011.5995427
- Karacali B, Snyder W (2002) Partial integrability in surface reconstruction from a given gradient field. In: Proceedings. Int. Conf. Image Process., vol 2 (IEEE, 2002), pp II-525–II-528. https://doi.org/10.1109/ICIP.2002.1040003
- Padfield D (2010) Masked FFT registration. In: Proc. IEEE Comput. Soc. Conf. Comput. Vis. Pattern Recognit, pp 2918–2925. https://doi.org/10.1109/CVPR.2010.5540032
- Schardin H (1942) Die Schlierenverfahren und ihre Anwendungen. In: Ergebnisse der exakten naturwissenschaften. Springer, Berlin, Heidelberg, pp 303–439. https://doi.org/10.1007/BFb0111981