Save image without saturation / assign rendered image to python variable directly


I try to get the depth map of an image, not the normalized one but also the real depth.
I’m using the following shader:
Screen Shot 2020-02-23 at 16.15.30

However, I got a saturated image:

(In the rendered, I see that there is different values for each pixel but in the saved image, they are saturated such that all the whole area is 1.0)

I tried also to save it in HDR format but it still saturate the values:
Screen Shot 2020-02-23 at 17.21.19

How can I save it without the saturation?
(without normalization because I want the real value).

Moreover, I prefer the python scripting, so if I can render it and get the image directly without save it and then display it in python platforms, so it would be even better (but if you know only manually, so it’s also helpful)