How can I get output from a Tk canvas?
The Tk canvas has a postscript method which allows one to create an Encapsulated Postscript file describing the canvas. This works for images as of 8.3. To get better postscript support, as well as a generally enhanced canvas, get the Tk dash patch (http://purl.oclc.org/net/nijtmans/dash.html) by Jan Nijtmans (mailto:j.nijtmans@chello.nl) (part of 8.3+).
