Das Ungermänner Wiki

nice for i in page*pnm; do
    echo $i
    potrace -g $i;  pgmtopbm -threshold -value 0.5  ${i/pnm/pgm}> ${i/pnm/pbm}
    convert  ${i/pnm/pbm} png:smooth-${i/pnm/png}; img2eps -3 smooth-${i/pnm/png}
done

oder

for i in *pnm; do echo $i; convert $i -rotate 90 -monochrome -resize 35% -monochrome  pnm:${i/pnm/small.pnm}; done
for i in *small.pnm; do echo $i; pnmtotiff -g4 $i > $i.tif; done
for i in *small.pnm.tif; do echo $i; tiff2pdf $i > $i.pdf; done
pdftk image-0*small.pnm.tif.pdf cat out.pdf

oder

for i in out*.pgm; do
    echo $i
    convert $i -sharpen 15 -black-threshold 10000 -white-threshold 20000 -despeckle -type bilevel -monochrome -compress group4 ${i/pgm/tif}
done
tiffcp out*.tif all.tif
tiff2pdf -z -o Document.pdf all.tif