[GRASSLIST:9083] Raster-2-Vector Methodology Sugestions?

[Phillip J. Allen]

Hi all,

I have a scanned color topo map an would like to filter out the brown 
topo lines from blue rivers/grid lines and black writing, then vectorize 
them to have just a contour map.

So far I have not been very happy with the results.  And I was wondering 
if anyone has had any good experience and could share their steps to get 
good results.

I first ran i.cluster & i.maxlik, r.mapcalc to get the group that was 
mainly the contours, r.thin , and then converted them to vector.

thanks,

Phil