Ultrasonic C-Scan Image Processing Using Multilevel Thresholding for Damage Evaluation in Aircraft Vertical Stabilizer

In this paper, two shadow reduction algorithms have been proposed and implemented using CIE Lab color space.The task of performing shadow reduction is done by executing shadow detection, shadow removal and lastly shadow edge correction in a sequential order.The first proposed algorithm is implemented based on pixel illumination and color information meanwhile the second algorithm is carried out via thresholding of one or more CIE Lab color space channels.The outputs from both proposed algorithms are compared in terms of shadow detection accuracy and required processing period.The proposed methods shown some promising results.