Patent ID: 6771807
Filing Date: 2004-08-03
Classification: G06T

Abstract:
A method for detecting surface defects on a Printed Circuit Board (PCB) having at least one layer including components, said method comprising:providing a digital image of the PCB; identifying edges on the PCB image; providing a computer model for each component on the at least one layer of the PCB, the computer model of each component on the at least one layer including segments; detecting anomalies on the PCB image by comparing identified edges to the computer model; and for each detected anomaly, determining if the detected anomaly corresponds to a surface defect; wherein said edges identifying step includes: computing a numerical gradient on the PCB image to yield a gradient image; thresholding the gradient image to yield a thresholded image; skeletting the thresholded image; and finding edges on the skeletted image; thereby yielding at least one chain of pixels, and wherein said edges identifying step further includes: saving each of the at least one chain of pixels of the skeletted image as a vector of pixel co-ordinates; using the pixel co-ordinates to estimate a second derivative of the at least one chain of pixels; and estimating co-ordinates of a passage by zero of the second derivatives; whereby, the passage by zero corresponds to edges.