'Get the edge image for the outer contour (no inner holes)'

def getEdgeImage(self):

    retVal = cv.CreateImage((self.width(), self.height()), cv.IPL_DEPTH_8U, 3)
    cv.Zero(retVal)
    tl = self.topLeftCorner()
    translate = [((cs[0] - tl[0]), (cs[1] - tl[1])) for cs in self.mContour]
    cv.PolyLine(retVal, [translate], 1, (255, 255, 255))
    return Image(retVal)
