Automatic blemish detection in liquid crystal flat panel displays

Visual defects sometimes occur during the manufacturing of flat panel liquid crystal displays (LCDs). One class of defects includes a variety of blemishes variously called stain (English), mura (Japanese) or alluk (Korean). These blemishes appear as low contrast, non-uniform brightness regions, typically larger than single pixels. They are caused by a variety of factors such as non-uniformity distributed liquid crystal material and foreign particles within the panel. Such blemishes cannot be repaired. Automatic inspection systems, designed for pixel and line defect detection, have had difficulty accurately detecting and quantifying LCD blemishes. At present, most blemish detection is performed by human inspectors. This paper describes a recently developed automatic inspection system, which reliably detects, quantifies and classifies LCD blemishes in the presence of single pixel and line pixel defects that tend to obscure the subtle blemishes. The algorithm underlying this system, called MuraLookTM, uses conventional image processing operators such as convolutional filtering, morphological filtering and blob shape analysis under region-of-interest control in a novel combination to systematically separate each of over twenty different blemish patterns. Strength measures for each class of blemish are used under human operator control to grade each blemish as pass or fail. The paper discusses various types of defects in LCD panels and relates them to the MuraLook system defect class patterns. The architecture of the MuraLook defect detection system is described.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.