An active contour algorithm for detecting the circular features in a PCB x-ray image

Detection of circular information including drill holes and inside connection metal rings, plays a key role for the automatic inspection of a multi-layer printed circuit board (PCB). An approach is presented to automatically extract whole circular information from an x-ray image acquired from a multi-layer PCB. By analyzing the x-ray image with a series of some image processing procedures, the basic circular information can be obtained and be treated as an initial contour for further processing. An effective modular active contour is then presented to guide the initial contour to locate the circular information more precisely. Experimental analyses have shown that the proposed approach can reach at the performance of 0.5 pixel average error under 20% random noise added. Experiments on real PCB x-ray images have also confirmed the feasibility of the proposed approach.