21 research outputs found

    Application of EMD in fringe analysis: new developments

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    Empirical mode decomposition (EMD) based methods have been widely used in fringe pattern analysis, including denoising, detrending, normalization, etc. The common problem of using EMD and Bi-dimensional EMD is the mode mixing problem, which is generally caused by uneven distribution of extrema. In recent years, we have proposed some algorithms to solve the mode mixing problem and further applied these methods in fringe analysis. In this paper, we introduce the development of these methods and show the successful results of two most recent algorithms.NRF (Natl Research Foundation, S’pore)Published versio

    A Novel Camera Calibration Method Based on Polar Coordinate

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    <div><p>A novel calibration method based on polar coordinate is proposed. The world coordinates are expressed in the form of polar coordinates, which are converted to world coordinates in the calibration process. In the beginning, the calibration points are obtained in polar coordinates. By transformation between polar coordinates and rectangular coordinates, the points turn into form of rectangular coordinates. Then, the points are matched with the corresponding image coordinates. At last, the parameters are obtained by objective function optimization. By the proposed method, the relationships between objects and cameras are expressed in polar coordinates easily. It is suitable for multi-camera calibration. Cameras can be calibrated with fewer points. The calibration images can be positioned according to the location of cameras. The experiment results demonstrate that the proposed method is an efficient calibration method. By the method, cameras are calibrated conveniently with high accuracy.</p></div

    Average of intrinsic parameters under different noise levels.

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    <p>Average of intrinsic parameters under different noise levels.</p

    Multi-camera calibration board based on cameras’ positions.

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    <p>Multi-camera calibration board based on cameras’ positions.</p

    Standard deviations for parameters <i>α</i>,<i>β</i>,<i>γ</i>.

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    <p>Standard deviations for parameters <i>α</i>,<i>β</i>,<i>γ</i>.</p

    the standard deviations of <i>u</i><sub>0</sub> with 3 and 10 pictures.

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    <p>the standard deviations of <i>u</i><sub>0</sub> with 3 and 10 pictures.</p

    Real Pictures—the accurate calibration board is at the top, the polar coordinates calibration board is at the bottom.

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    <p>Real Pictures—the accurate calibration board is at the top, the polar coordinates calibration board is at the bottom.</p

    Standard deviations for parameters <i>u</i><sub>0</sub>, <i>v</i><sub>0.</sub>

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    <p>Standard deviations for parameters <i>u</i><sub>0</sub>, <i>v</i><sub>0.</sub></p

    Multi-camera calibration board with known positions of centers.

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    <p>Multi-camera calibration board with known positions of centers.</p

    Multiple-camera calibration board.

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    <p>Multiple-camera calibration board.</p
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