Noise Elimination for Image Subtraction in Printed Circuit Board Defect Detection Algorithm

Image subtraction operation has been frequently used for automated visual inspection ofprinted circuit board (PCB) defects. Even though the image subtraction operation able to detect alldefects occurred on PCB, some unwanted noise could be detected as well. Hence, before the imagesubtraction operation can be applied to real images of PCB, image registration operation should bedone to align a defective PCB image against a template PCB image. This study shows how theimage registration operation is incorporated with a thresholding algorithm to eliminate unwantednoise. The results show that all defects occurred on real images of PCB can be correctly detectedwithout interfere by any unwanted noise.