FUNCTION rev_true_image, image
; reform a true-color image of (m x n x 3) to (3 x m x n), conforming to write_png
sz=size(image,/dim)
if sz[2] eq 3 then begin
  r=image[*,*,0]
  g=image[*,*,1]
  b=image[*,*,2]
  
  im=bytarr(3,sz[0],sz[1])
  im[0,*,*]=r
  im[1,*,*]=g
  im[2,*,*]=b
  return,im
endif else begin
  print,'nothing done, as the image dimension does not match.'
  return,0
endelse
END