Font metrics. The only way to generate accurate images in any format that contain text is to know the font metrics. Specifically, we need to know the width of every character and the maximum height (since we want all characters to fit within same line height). I used ttf2tfm to dump the font metrics from Mac TrueType fonts and then converted that to a Java class for use in a PostScript generator for trees. Commands:

	 $ ttf2tfm /Library/Fonts/Arial\ Black.ttf > metrics
 

Then run metrics into python code after stripping header/footer:

	 #
	 # Process lines from ttf2tfm that look like this:
	 # Glyph  Code   Glyph Name                Width  llx    lly      urx    ury
	 # ------------------------------------------------------------------------
	 #     3  00020  space                       333  0,     0 --     0,     0
	 #
	 lines = open("metrics").read().split('\n')
	 print "public class FontName {"
	 print "    {"
	 maxh = 0;
	 for line in lines[4:]: # skip header 0..3
			 all = line.split(' ')
			 words = [x for x in all if len(x)>0]
			 ascii = int(words[1], 16)
			 height = int(words[8])
			 if height>maxh: maxh = height
			 if ascii>=128: break
			 print "        widths[%d] = %s; // %s" % (ascii, words[3], words[2])

	 print "        maxCharHeight = "+str(maxh)+";"
	 print "    }"
	 print "}"
 

Units are 1000th of an 'em'.