1. A method comprising: performing a thinning process of an image to output a thinned one-pixel-width line drawing using a processor; extracting contour vector sequences that surround each of line elements of the thinned one-pixel-width line drawing, using the processor, wherein the line elements correspond to one-pixel-width lines connecting terminal points and intersections of the thinned one-pixel-width line drawing; and generating skeletonized vector data that surround each of zero-width line elements by shifting positions of the extracted contour vector sequences that surround each of the line elements of the thinned one-pixel-width line drawing, using the processor.