convert --> mkbitmap --> potrace

text.sh

for file in ./Layers\ PNG/*.png; do
    filename=$(basename -- "$file")
    filename=${filename%.*}
    convert $file ./Layers\ BMP/"${filename}.bmp"
done

for file in ./Layers\ BMP/*.bmp; do
    filename=$(basename -- "$file")
    filename=${filename%.*}
    mkbitmap -o ./Layers\ PBM/"${filename}.pbm"  -x -t 0.9 -i -b 20  $file
done

for file in ./Layers\ PBM/*.pbm; do
    filename=$(basename -- "$file")
    filename=${filename%.*}
    potrace --eps --flat -C '#0000FF'  --opaque --width 11.5in --height 11.5in -r 600 $file -o ./Layers\ EPS/"${filename}".eps 
done