Practical Guide:

plot("filename")....;   // plot something
png::print("file.png","-transparent rgb:ff/ff/ff");
    // print it to a png file named file.png
    // the second argument is the options to beps2png

This is a terminal derived from blopeps: first a blopeps file is created, and then it is transformed to a png file using the beps2png tool of blop. The static print(filename,opts) function of the png terminal can be used to print the current canvas to a file specified by the first argument, the second argument specifies the options to be given to beps2png (see beps2png --help for help)

Source files:
   png.h
   png.cc