Your graph specification should not be wrapped with the .G1 and .G2 macros that normally guard it within groff(1) macros.
The output image will be a black-on-white graphic clipped to the smallest possible bounding box that contains all the black pixels. By specifying command-line options to be passed to convert(1) you can give it a border, set the background transparent, set the image's pixel density, or perform other useful transformations.
This program uses grap(1), pic(1), groff(1), and the ImageMagick convert(1) program. These programs must be installed on your system and accessible on your $PATH for grap2graph to work.
Command-line switches and arguments not listed above are passed to convert(1).