private boolean isNeighbourOfMarkedPixel(int aX, int aY)
    {
        return (      pixelIsMarked(aX - 1, aY)
                  ||  pixelIsMarked(aX + 1, aY)
                  ||  pixelIsMarked(aX, aY - 1)
                  ||  pixelIsMarked(aX, aY + 1)
                  ||  pixelIsMarked(aX - 1, aY - 1)
                  ||  pixelIsMarked(aX + 1, aY - 1)
                  ||  pixelIsMarked(aX + 1, aY + 1)
                  ||  pixelIsMarked(aX - 1, aY + 1) );
    }