I’ve a .png file representing the phase diagram of argon. I need to represent in the graph the point (x,y)=(0.8072,0.7866), where the coordinates are according to the axes in the image, to see what is the corresponding phase. I’ve tried with the open source program plot digitizer (https://web.eecs.utk.edu/~dcostine/personal/PowerDeviceLib/DigiTest/index.html), but it permits only to click on the graph, add a point data and see the corresponding coordinates, not the other way round. I’ve tried with python with the following code:

from PIL import Image

import matplotlib.pyplot as plt
import numpy as np
img = np.asarray(Image.open(r"C:UsersutenteDesktopLJ_PhaseDiagram.png"))
print(repr(img))
%matplotlib
imgplot = plt.imshow(img,extent=[0, 1000, 0, 1000])

But it’s difficult to align the axes.