Python functions that return the dpi of the main screen, and the x/y size of the image in inch in order to resize the plot automatically.

matplotlib_auto_image_size.py

import ctypes
import tkinter

def get_dpi():
    ctypes.windll.shcore.SetProcessDpiAwareness(1)
    root = tkinter.Tk()
    dpi = ctypes.windll.user32.GetDpiForWindow(root.winfo_id())
    root.destroy()
    return dpi

def get_inches_plot(array):
    dpi = get_dpi()
    return array.shape[1]/dpi, array.shape[0]/dpi

Example

quality:float = 2
fig = plt.figure()
fig.set_size_inches(get_inches_plot(img))             <---
plt.axis('off')
plt.imshow(img)
plt.savefig(filepath, dpi=get_dpi()*quality)          <---
plt.show()

quality is the detail of the image