Line defect detection in Tft-Lcd using directional filter bank and adaptive multilevel thresholding

This paper uses a Directional Filter Bank (DFB) and adaptive multilevel thresholding for TFT-LCD panel inspection. Line-scan and area-scan cameras are used to acquire images of TFT-LCD panels with different resolutions. Thereafter, a DFB is used to find line defects in low-resolution images, while adaptive multilevel thresholding is employed to detect line defects on the LCD panels. LCD panel defects can be defined as the pixels that have a non-uniform bright region compared to the background region. However, the intensities of LCD panels are inherently non-uniform, the pattern-variation different even within the same model, and defects usually faint and hard to discern, making the detection problem all the more difficult. Accordingly, the present study detects line-type defects by using a DFB and multilevel threshold to extract features. In a low-resolution image, a DFB that can find directional information is used to identify a line-shape abnormal region. Meanwhile, in a high-resolution image, a multilevel thresholding technique based on statistical approach is employed to detect abnormal line defects that are brighter or darker than the surrounding pixels. The effectiveness of the proposed DFB and multilevel thresholding technique is tested through the experiments using real LCD panels.