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- 저자 : Zhaobing Hao (검색결과 2 건)
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Guan Xu,Lina Sun,Jian Su,Zhaobing Hao,Xue Lu,Xiaotao Li 한국광학회 2014 Current Optics and Photonics Vol.18 No.4
In vision measurement systems based on structured light, the key point of detection precision is to determine accurately the central position of the projected laser line in the image. The purpose of this research is to extract laser line centers based on a decision function generated to distinguish the real centers from candidate points with a high recognition rate. First, preprocessing of an image adopting a difference image method is conducted to realize image segmentation of the laser line. Second, the feature points in an integral pixel level are selected as the initiating light line centers by the eigenvalues of the Hessian matrix. Third, according to the light intensity distribution of a laser line obeying a Gaussian distribution in transverse section and a constant distribution in longitudinal section, a normalized model of Hessian matrix eigenvalues for the candidate centers of the laser line is presented to balance reasonably the two eigenvalues that indicate the variation tendencies of the second-order partial derivatives of the Gaussian function and constant function, respectively. The proposed model integrates a Gaussian recognition function and a sinusoidal recognition function. The Gaussian recognition function estimates the characteristic that one eigenvalue approaches zero, and enhances the sensitivity of the decision function to that characteristic, which corresponds to the longitudinal direction of the laser line. The sinusoidal recognition function evaluates the feature that the other eigenvalue is negative with a large absolute value, making the decision function more sensitive to that feature, which is related to the transverse direction of the laser line. In the proposed model the decision function is weighted for higher values to the real centers synthetically, considering the properties in the longitudinal and transverse directions of the laser line. Moreover, this method provides a decision value from 0 to 1 for arbitrary candidate centers, which yields a normalized measure for different laser lines in different images. The normalized results of pixels close to 1 are determined to be the real centers by progressive scanning of the image columns. Finally, the zero point of a second-order Taylor expansion in the eigenvector’s direction is employed to refine further the extraction results of the central points at the subpixel level. The experimental results show that the method based on this normalization model accurately extracts the coordinates of laser line centers and obtains a higher recognition rate in two group experiments.
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Three Degrees of Freedom Global Calibration Method for Measurement Systems with Binocular Vision
Guan Xu,Xinyuan Zhang,Xiaotao Li,Jian Su,Xue Lu,Huanping Liu,Zhaobing Hao 한국광학회 2016 Current Optics and Photonics Vol.20 No.1
We develop a new method to globally calibrate the feature points that are derived from the binocularsystems at different positions. A three-DOF (degree of freedom) global calibration system is establishedto move and rotate the 3D calibration board to an arbitrary position. A three-DOF global calibration modelis constructed for the binocular systems at different positions. The three-DOF calibration model unifiesthe 3D coordinates of the feature points from different binocular systems into a unique world coordinatesystem that is determined by the initial position of the calibration board. Experiments are conducted onthe binocular systems at the coaxial and diagonal positions. The experimental root-mean-square errorsbetween the true and reconstructed 3D coordinates of the feature points are 0.573 mm, 0.520 mm and0.528 mm at the coaxial positions. The experimental root-mean-square errors between the true andreconstructed 3D coordinates of the feature points are 0.495 mm, 0.556 mm and 0.627 mm at the diagonalpositions. This method provides a global and accurate calibration to unity the measurement points ofdifferent binocular vision systems into the same world coordinate system.
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