The script pgf2bitmap.sh takes an pgf formatted image and converts it into a bitmap file (png,jpg,..).
-d, --density
Dpi, either for horizontal and vertical direction seperately (e.g. "300x400") or for both directions (e.g. "400").
Defaults to "300"
See also man page for convert
-t, --type
Type of output so e.g. "jpg"
Defaults to png
All other unrecognized given arguments are used as "output-options" for the convert command.
I had to comment out the line <policy domain="delegate" rights="none" pattern="gs" /> in the policy file of ImageMagick in /etc/ImageMagick-7/policy.xml. See here.