Blender python (bpy) rendering incorrect depth

Question

I am new to blender. I am trying to render RGB composite images, albedo and depth map of the context scene in blender. RGB images are rendered well, but the depth image is renderer incorrectly.

I am normalizing the input before passing it to the render layer output node.

def depth(self, normalize=True):
    self.__original(True)
    render = self.tree.nodes['Render Layers']
    composite = self.tree.nodes['Composite']
    norm = self.tree.nodes['Normalize']
    self.__linkNodes(render, norm, out=2)
    self.__linkNodes(norm, composite)

Please help me identify and fix the issue with depth rendering. Thanks