Syncing matplotlib imshow coordinates

I'm trying to create an image using networkx, save that image to use later, and then overlay a plot over top of it later. However, when I try to load the image in and make new points, the scale seems off. I've tried everything I can find to make them sync, and I'm not sure what else to try at this point. Here's a simple example:

import networkx as nx
import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure()
G = nx.dodecahedral_graph()
pos = nx.spring_layout(G)
plt.box(False)
nx.draw_networkx_edges(G, pos=pos)
fig.canvas.draw()

data = np.array(plt.gcf().canvas.get_renderer().buffer_rgba(), dtype=np.uint8)
extent = list(plt.xlim() + plt.ylim())

So now I have a graph and have saved that image to data, and have saved the range of that graph to extent. I then want to replot that graph from data and overlay the nodes of the graph, in the positions stored in pos.

plt.imshow(data, extent=extent)
plt.box(False)
nx.draw_networkx_nodes(G, pos=pos, node_color='green')

For some reason, the scale of the original image is shrunk, so the nodes end up being at a larger scale and not matching the edges. Is it something in the way I'm saving the image?

It seems that matplotlib adds padding to the sides of the image when saving the data from the plot. You can remove this padding by adding fig.tight_layout(pad=0) to the code like so:

import networkx as nx
import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure()
G = nx.dodecahedral_graph()
pos = nx.spring_layout(G)
plt.box(False)
nx.draw_networkx_edges(G, pos=pos)
fig.tight_layout(pad=0)
fig.canvas.draw()

data = np.array(plt.gcf().canvas.get_renderer().buffer_rgba(), dtype=np.uint8)
extent = list(plt.xlim() + plt.ylim())