Perhaps xdvi is a good start point to understand how to convert dvi to raw images. dvi isn't a ready to display format you have to prepare the missing glyphs (fonts). Knuth has provided a converter to make dvi files human readable and you task is to interpret this output. If you take a viewer as a start point you could store the fineshed rendering in a file instead of saving that. Like ps dvi is also a virtual machine code but much simpler.