Visual defect inspection of touch screens using multi-angle filtering in curvelet domain

Abstract

Touch screens are widely used in smartphones and tablets. These screens exhibit a pattern of directional, regular lines on their surface. The intricate texture of this background, which quickly causes interference, poses a significant challenge in detecting surface defects. Surface defects can be mainly classified into two types: linear and planar. Existing methods cannot effectively detect both types of defects. This study proposes a curvelet transform-based multi-angle filtering method. It can effectively attenuate regular patterns from panel images with textural backgrounds and preserve fine linear and planar defects in the reconstructed image. Curvelet transform is a multi-scale directional transformation that can capture the curved edges of objects well. The filtered curvelet coefficients are then reconstructed into the spatial domain and binarized using a threshold based on the interval estimation skill. The results of the trial show that the suggested approach can precisely locate and identify defects in touch panels. The rate of defect detection (1-β) stands at 93.33 %. The rate of defect misjudgment (α) is at a low of 1.26 %. The correct classification rate (CR) is impressively high at 98.69 %, indicating that the proposed method provides fine-grained segmentation results over existing methods for detecting surface defects on touch panels.