Generate a PostScript (Encapsulated PostScript, version 3.0) representation of part or all of the canvas. If the file or channel option is given, the PostScript is written there and an empty string is returned; otherwise it is returned as a string. By default only the area currently visible in the window is generated, so it is usually necessary either to call update() first or to use the width and height options. Supported options include colormap, colormode, file, fontmap, height, pageanchor, pageheight, pagewidth, pagex, pagey, rotate, width, x and y.