PNG to 3d object for 3d printing

convert.sh

#!/bin/sh
for f in *.png
do
	filename=${f%.*}
	echo "Processing $filename"

	# png -> bmp
	convert $filename.png -normalize -fx 'a==0 ? white : u' $filename.bmp
	
	# trace bitmap to eps
	potrace $filename.bmp -o $filename.eps

	# eps -> dxf
	pstoedit -dt -f "dxf: -polyaslines -mm" $filename.eps $filename.dxf

	# extrude vector image to 3d model with openscad
	openscad -o $filename.stl -D "image=\"$filename.dxf\"" generate.scad
done

generate.scad

linear_extrude(height = 2, center = true, convexity = 10)
	import(file = image);

This basically works, but my dimensions are wrong. Do I need to scale the input files to a specific resolution for this to work correctly?