python opencv with docker: Matplotlib.show Matplotlib is currently using agg, which is a non-GUI backend

Question

I need to run opencv + python in docker.

This code should show a GUI popup with an image:

import cv2
from matplotlib import pyplot as plt
img = cv2.imread("image.jpg")
img_gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
img_rgb = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
plt.subplot(1, 1, 1)
plt.imshow(img_rgb)
plt.show()

It works fine on a ubuntu desktop but the problem is with docker. I got this error:

UserWarning: Matplotlib is currently using agg, 
which is a non-GUI backend, so cannot show the figure.
  plt.show()

Following some post, if I add this

import matplotlib
matplotlib.use('TkAgg')

I got another similar error:

ImportError: Cannot load backend 'TkAgg' which 
requires the 'tk' interactive framework, as 
'headless' is currently running

attempts

• I installed tinker
• I launched the container with .Xauthority && /tmp/.X11-unix/X0
• I tried almost all the answers of
  • "UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure." when plotting figure with pyplot on Pycharm
  • How can I use matplotlib.pyplot in a docker container?
  • Tails - Package 'python3-tk' has no installation candidate
• Almost every answer is for os with desktop, not for docker

workaround

I know that runs GUI applications is not the goal of docker, but I want to use docker to have my operative system clean while I developing on python.

If I change the show() by plt.savefig("mygraph.png") , the image is created instead the gui popup.

steps to replicate the issue with ubuntu

• docker run

docker run -it  \
--workdir=/app \
-v /your/workspace:/app \
-v /tmp/.X11-unix/X0:$XSOCK -e DISPLAY=0  \
jjanzic/docker-python3-opencv  bash

• install matplotlib

pip install matplotlib

• add the python code and run it with: python main.py