Raster-to-vector conversion by line fitting based on contours and skeletons

A new raster-to-vector conversion method is proposed for capturing high-quality vectors from line drawing images in which the lines are overlapped by characters, symbols, or other lines. Conventionally, two raster-to-vector conversion methods have generally been used. One is a thinning method. The other is a medial line extraction method based on parallel pairs of contours. The thinning method tends to distort extructed lines, especially of intersections and corners. On the other hand, the medial line extraction method has poor capabilities as regards capturing correct lines at intersections. In contrast, the method proposed can extract precise lines from both contours and skeletons. Contours are able to hold edge shapes well, while skeletons preserve topological features; thus, a combination of these features effectively leads to the best fitting line. In the proposed method, the line which best fits the original image is selected from among various candidate lines. The candidates are created from several merged short skeleton fragments located between pairs of short contour fragments. The method is also extended to circular arc fitting. Experimental results show that the method is effective