The line-structured light vision sensor is widely used in 3D reconstruction and scanning, quality inspection and other fields. In this technique, the segmentation of light stripe image is an important preprocessing steps, which separates light stripe and extract ROI from an original image. The segmentation of light stripe is the basis of centerline extraction and also affects the efficiency of centerline extraction. In our work, the 3D reconstruction of wood surface needs to be realized through using line-structured light sensor, and then the 3D defects need to be detected. The measured wood has a curved, rough and scattering surface. The acquired light stripe is relative complex. Several algorithms of image segmentation are studied, and the segmentation performance and operation efficiency are compared and analyzed, so as to help us find the optimum technique.
In the real-time structured light 3D measurement, there are issues such as low throughput and slow measurement speed in the extraction of light stripe centerline by computer software and hardware processors like ARM. This paper designs a real-time system for extracting the light stripe centerline based on the ZYNQ-7000. Firstly, the thresholding segmentation of light stripe image is implemented by using the Otsu’s method. Secondly, the Gaussian filter is used to remove the effect of noise. Finally, the centerline of light stripe is extracted by using the grayscale gravity method. The image processing algorithm is converted from C++ to Verilog language and packaged into an IP core using the Xilinx HLS tool. This paper successfully processes the input video signal with the spatial resolution of 1920×1080 pixels and displays the extracted centerline of light stripe on the HDMI display at the frame rate of 30 fps. The test results show that the system can meet the real-time requirement for light stripe centerline extraction in the engineering application.
The ice cream stick is a kind of wood product with a plane surface. For the qualified stick it has the nearly flat surface. However, due to slender and thin shape the bend defect is prone to occur during machining of ice cream stick. At present, manual technique is often used to identify the bend defect in the industrial fields, which holds many problems such as low efficiency, low automation and unreliable detection result. In the paper, the PCA-based bend feature selection method is proposed which is applied in defect detection of ice cream stick. At first, the 3D data of object surface is obtained based on the three-dimensional (3D) measurement principle of line structured light. Then four kinds of bend features are designed according to the shape characteristics of the light stripe, which include variation coefficient, correlation coefficient, determination coefficient and straightness metric. At last, the bend feature selection is operated based on the PCA-based method. The research results provide valuable reference for the engineering application in the intelligent defect detection.
In the accuracy measurement of phase from interferometers with adjustable fringe contrast, it needs to estimate the contrast of experimental patterns so as to obtain the interference patterns with the maximum contrast. We develop the Fourier-polar transform and combine the directional projection to estimate the global contrast of carrier fringe pattern. The technique is especially used for low-quality fringe pattern such as low contrast and low signal to noise ratio (SNR) that often appear in the interferometric experiment. An illustrative experiment based on the radial shearing interferometer is given. Results generated from this technique are compared with the derived values from theoretical model, and exemplary agreement between both is demonstrated.
In the 3D phase measurement with large view field, when the number of fringes is not too many, the period broadening problem of projection fringes will seriously affect the accuracy of measurement. In this paper, an accurate and convenient 3D shape measurement method based on phase shifting fringe projection is prop osed. Firstly, in the fringe projection measurement system based on the triangulation principle, the fringe position coordinates are taken as the input and output parameters of the system, and the linear mathematical model of fringe period correction is de rived. Secondly, the model parameters are obtained by simple calibration process. Through using the idea of reverse fringe projection, the new fringe to be projected is calculated from the correction model, and then periodic four-step phase shifting projection fringes can be produced. Finally, a four-step phase shifting method is used to restore the 3D shape of object. The experiments of fringe period correction and 3D profile measurement show that the proposed method can easily generate the phase-shifting projection fringes with equal period distribution and hence improve the measurement accuracy of phase-shifting method.
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