 given height are very fast as
 the pre-computed templates are used and no display/screen capture is
 needed.

 USAGE
  masks = char2img( strings, h, [pad] )

 INPUTS
  strings  - {1xn} text string or cell array of text strings to convert
  h        - font height in pixels
  pad      - [0] amount of extra padding between chars

 OUTPUTS
  masks    - {1xn} binary image masks of height h for each string

 EXAMPLE
  mask=char2img('hello world',50); im(mask{1})
  mask=char2img(num2str(pi),35); im(mask{1})

 See