Vectorizing Palladio's engravings

Get the image from rarebookroom.org

wget http://www.rarebookroom.org/NewOctavoImages/pldarc/LargePhotos/pldarc0153.jpg

Create a threshold image

convert detail.png -threshold 75% mask.png

Use that as mask to clean up the original image

convert detail.png mask.png    -compose Screen  -composite  detail_mask_screen.png

Vectorize the image

convert detail_mask_screen.png -format pnm pnm:- |potrace -s > detail_mask_screen.svg