Homebrew PCBs

Cristian,
Are you looking to use a CNC to do milling, or are you looking to 
minimize chemical use?  The reason I ask is that the algorithm for the 
minimizing chemical use is easier to implement than the one for the CNC 
milling.  If you take the 'round' bmp and erode the white one pixel 
width at a time until the minimum width you want (say 2 pixels wide) is 
achieved, that will work for chemical etching, but will not optimize for 
mechanical.  To do that, you have to get into graph theory, minimum 
spanning trees, TSP,  and the like.
I could probably do the image one for you, if you are interested.
Richard