docs: def tricolor_white_bg(self, img):
          """transforms image from RGB with (0,0,0)
          showing black to  RGB with 0,0,0 showing white
  
          takes the Red intensity and sets
          the new intensity to go
          from (0, 0.5, 0.5) (for Red=0)  to (0, 0, 0) (for Red=1)
          and so on for the Green and Blue maps.
  
          Thus the image will be transformed from
            old intensity                new intensity
            (0.0, 0.0, 0.0) (black)   (1.0, 1.0, 1.0) (white)
            (1.0, 1.0, 1.0) (white)   (0.0, 0.0, 0.0) (black)
            (1.0, 0.0, 0.0) (red)     (1.0, 0.5, 0.5) (red)
            (0.0, 1.0, 0.0) (green)   (0.5, 1.0, 0.5) (green)
            (0.0, 0.0, 1.0) (blue)    (0.5, 0.5, 1.0) (blue)
  
          """
          tmp = 0.5*(1.0 - (img - img.min())/(img.max() - img.min()))
          out = tmp*0.0
          out[:,:,0] = tmp[:,:,1] + tmp[:,:,2]
          out[:,:,1] = tmp[:,:,0] + tmp[:,:,2]
          out[:,:,2] = tmp[:,:,0] + tmp[:,:,1]
          return out