subr tvreadrgb, win, red, green, blue
 x = tvread(win)
 nx = dimen(x,0)   ny = dimen(x,1)
 x = bmap(x)
 redim,x,4,nx,ny
 if $little_endian then {
   red = x(2,*,*)
   green = x(1,*,*)
   blue = x(0,*,*)
 } else {
   red = x(1,*,*)
   green = x(2,*,*)
   blue = x(3,*,*)
 }
 endsubr
 ;========================================================