I want to digitize the roads of a raster map to vector format using QGIS and GDAL preferably. By using the Raster Calculator I have been able to extract the roads and contour-lines from the raster to another raster by selecting pixels of the right color. The problem now is that I don't want the contour-lines, just the roads. The difference here is that the contour-lines are much thinner than the roads.
I have been trying to use Sieve and Proximity without much luck. I think I want something similar to Shrink in ArcGIS or maybe use different settings. Here is my start image which has gone through Raster calculation and a Proximity filter.