Wenyan Tang

Multilevel thresholding selection based on variational mode decomposition for image segmentation

Abstract Multilevel thresholding techniques based on gray histogram are usually computationally expensive for the image segmentation. In this paper, we propose a novel thresholding extraction method based on variational mode decomposition (VMD). The improved VMD is used to decompose the histogram non-recursively into several sub-modes for minimizing Otsus objective function. Then, we can extract the thresholds easily by the minimum point search (MPS) method or the cross point search (CPS) method. The experimental results demonstrate that the proposed MPS scheme exhibits more excellent capability than CPS. Further, compared with other approaches namely particle swarm optimization algorithm (PSO), fuzzy c-means (FCM) algorithm and bacterial foraging (BF) algorithm, the proposed algorithm can get similar performance, but its computing speed is faster than others. Therefore, it could have some advantages in image preprocessing, such as fast target recognition and classification.

A universal precision positioning equipment in coordinate unified for large scale metrology

In this article we describe the design of universal precision positioning equipment and the method to be used in the multi stations coordinate unified of large scale measurements. The system incorporates the concept of distance constrains to control the random error of common points. Measuring each point of the artifacts with the coordinate measuring machine which have higher accurate and obtaining the spatial geometry relationships of them. Used the coordinate data of measurements on site in artifacts to obtain the spatial geometry relationships and compared them with the calibrated relationships. Simultaneously can find the large error of the common points and controlled the error in a set range to achieve the traceability of measurement on site. Then use the common points which satisfied the setting range to transform the coordinate to reference. We get a higher precision coordinate unified with the algorithm of 7 parameters Procrustes. The present method is used in coordinate unified for electronic theodolites and laser tracker. The results show that the accuracy using the artifact is much better than traditional method.

Direct radius compensation and evaluation method for quadric surface at arbitrary position in space

A direct radius compensation and evaluation method for quadric surface at arbitrary position in space with coordinate measuring machining (CMM) is proposed. The radius error is compensated by the optimization model directly based on minimum condition principle with the object function value calculated by angle subdivision approach algorithm. The model is optimized by Improved Particle Swarm Optimization (IPSO) algorithm. Particle Swarm Optimization (PSO) improved by the idea of optimized analytical method, natural selection and crossover with the maximum distance as the object function based on minimum condition principle is proposed. In the experiment, the direct method and the usual method based on B-spline are employed to evaluate the quadric profile error and compare. The direct method result is 0.1811mm, more accurate than the usual method result 0.2522mm. Experimental evidence shows that the direct method is robust and efficient.