In some cases, I needed to process a raster-to-vector conversion. There are at least 2 ways to do that: the hard way and the lazy way.
In short, the hard way is to open original image in vector drawing software and redraw all the paths by hand: boring, painfull, not for me.
The conversion process is to convert from PNG to PNM then from PNM to SVG.
First step done with ImageMagick:
convert image.png image.pnm
Second step done with Potrace:
potrace -s -o image.svg image.pnm
And finally you can remove temp pnm file.