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In the detection of small and weak defect targets in ink area of planar glass element of a mobile phone，using linear array camera with dark field illumination and line-by-line scanning imaging system will result in the size of image (30720 *16384) much larger than the size of small defect targets (3 pixels) . At the same time, because the stains are located in the ink area, the contrast between the defect target and the background of the ink area could be very low. This will lead to the weak defect targets in the ink area could not be detected quickly and effectively using the common target detection method. In order to solve this problem, a detection method of small and weak defects in the ink area of planar glass element based on self-correlation template matching and one-dimensional maximum entropy is proposed in this paper. Firstly, the large-scale image is first clipped, and the character information in the ink area is recognized and fixed position using the self-correlation template matching algorithm. The character and Logo information in the ink area are clipped according to the positioning results. Secondly, the processed image is clipped twice and binarized by the OTSU method. BLOB technology is used to select the largest white area as the ink area in the second clipping image. Thirdly, Sobel operator is used to detect the edge of the ink area, and the transitional area with the width of 100 pixels on the edge of the ink area is clipped, so the clipping image of the ink area which only contained valid small and weak defect targets is obtained. Finally, One-dimensional maximum entropy algorithm is used to separate the defect targets from real ink area, and the weak and small defect targets are recognized and detected by BLOB technology. The experimental results show that the method solves the problem of detecting the small and weak defects in the ink area of the planar glass element with fast recognition speed and high detection accuracy. It can be applied in the process of detecting the quality and cleanliness of planar glass element, and has great significance for improving the quality and efficiency of mobile phone production and assembly.
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