##
from tkinter import *
tk = Tk()
canvas = Canvas(tk, width=700, height=789)
canvas.pack()
canvas.create_oval(400,400,700,700, fill="red")
tk.update()
canvas.postscript(file="my_dram.png", colormode="color")
# после создания нашего PS
canvas.postscript(file="my_dram.ps", colormode="color")
# преобразовываем в PNG
from PIL import Image
img = Image.open("my_dram.ps")
img.save("my_dram.png", "png")