#### write bitmap from current display ####
-------------------------------------------
funct (left-click): write 24bit TIFF/RGB file
  set rgb <outfile>
  save_rgb
-------------------------------------------
funct (middle-click): write transparent-bg TIFF/RGB
  set black2transparent 1
  set rgb <outfile>
  save_rgb
-------------------------------------------


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

-------------------------------------------
funct (left-click): write 24bit TIFF/RGB file
  set rgb <outfile>
  save_rgb
-------------------------------------------

A default left-click on the "W" button on the
"rgb:" entry line writes out the current surface
view in GL window as a 3-byte/pixel TIFF file
(after name expansion if '~' or '*'-abbreviated).

Must confirm overwrite (tcl funct, save_rgb,
doesn't ask overwrite).  Ignores mouse cursor,
pops window to front, and redraws before saving.

Untick nearby checkbutton ($tiffoutflag) to write
SGI *.rgb file instead.

To save cursor and/or timecourse overlay (cleared
on redraw), use adjoining "WN" button instead.
In that case, be sure there are no overlapping
windows before saving.

-------------------------------------------
Alt funct (left-click): write transparent-background TIFF/RGB
  set black2transparent 1
  set rgb <outfile>
  save_rgb
-------------------------------------------

If the "W" 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.
