光电工程, 2016, 43 (3): 7, 网络出版: 2016-09-12   

基于二维 DFT的 TFT-LCD平板表面缺陷检测

Surface Defect Inspection of TFT-LCD Panels Based on 2D DFT
作者单位
合肥工业大学仪器科学与光电工程学院,合肥 230009
摘要
为了检测 TFT-LCD平板表面缺陷,搭建了自动光学检测 (AOI)实验系统,提出了一种基于二维 DFT的缺陷检测算法。通过霍夫变换 (HT)检测到代表线状纹理的高能量频域直线,将位于直线邻域内的频率成分置 0,再经过二维 IDFT进行空间域图像重构,来移除方向性线状纹理背景,最后经过简单的阈值算法将缺陷从背景中提取出来。在对高能量频域直线的斜角计算时,利用数学统计解决了如何自动选取频域中高能量阈值以及如何从斜角直方图中自动提取各个峰值点这两个关键问题。在重构图像时,在以傅里叶频谱中心为圆心的圆环内,设置圆环内的频率成分不变,很好地保护了方向接近方向纹理的缺陷不被移除。实验结果表明,对包含纤维、污点和划痕的 TFT-LCD平板表面缺陷,检测结果完全正确,证明了该检测算法具有良好的实用性与鲁棒性。
Abstract
In order to detect the surface defects of TFT-LCD panel, an Automated Optical Inspection (AOI) experimental system was built and a defect detection algorithm was proposed based on two-dimensional (2D) DFT. The lines associated with high-energy frequency components in the spectrum that represented linear texture could be detected by Hough Transform (HT), and the corresponding neighborhood of high-energy frequency components were set to zero, and then a spatial domain image was reconstructed using the two-dimensional IDFT to remove the background of directional linear texture. Moreover, a simple threshold algorithm was used to discriminate the defects from the background. When calculating the slope-angle of high-energy frequency components in Fourier domain, two key points of how to select the high-energy threshold in frequency domain and how to extract the peaks from the angle histogram automatically were solved by using mathematical statistics. To preserve the defect, whose direction is near to directional-textures in the reconstructed image, all frequency components lying within a small annulus with the DC as the center in Fourier domain must be retained. The experiments on a variety of surface defects such as fibers, stains and scratches in TFT -LCD panel testified the effectiveness and robustness of the proposed method.

张腾达, 卢荣胜, 张书真. 基于二维 DFT的 TFT-LCD平板表面缺陷检测[J]. 光电工程, 2016, 43(3): 7. ZHANG Tengda, LU Rongsheng, ZHANG Shuzhen. Surface Defect Inspection of TFT-LCD Panels Based on 2D DFT[J]. Opto-Electronic Engineering, 2016, 43(3): 7.

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