A. Halim, M., N. Ruhaiyem, E. Fauzi, M. Jamil, and A. Mohamed. “Automatic Laser Welding Defect Detection and Classification Using Sobel-Contour Shape Detection”. Journal of Telecommunication, Electronic and Computer Engineering (JTEC), vol. 8, no. 6, Sept. 2016, pp. 157-60, https://jtec.utem.edu.my/jtec/article/view/1266.