#### write bitmap from current display ####
-------------------------------------------
funct (left-click): write 24bit TIFF/RGB file
  [no redraw]
  set rgb <outfile>
  save_rgb
-------------------------------------------
funct (middle-click): write transparent-bg TIFF/RGB
  [no redraw]
  set black2transparent 1
  set rgb <outfile>
  save_rgb
-------------------------------------------


Detailed Description of "rgb:" line "WN" Button Actions

-------------------------------------------
funct (left-click): write 24bit TIFF/RGB file
  [no redraw]
  set rgb <outfile>
  save_rgb
-------------------------------------------

A default left-click on the "WN" button (write,
no redraw) is the same as left-clicking the "W"
button, except there is no pop/redraw, so tmp
overlays (e.g., cyan cursors, rawdata time
courses) will also be saved into bitmap.

N.B.: any overlapping window will be saved into
bitmap so first manually unoverlap the image
window.

-------------------------------------------
Alt funct (left-click): write transparent-background TIFF/RGB
  [no redraw]
  set black2transparent 1
  set rgb <outfile>
  save_rgb
-------------------------------------------

If the "WN" button is middle-clicked, a
4-byte/pixel tiff with the black background
converted to transparent is written.  This is
useful for making figures with overlapping
images.
