如何在tkinter中实现opencv selectROI？

import tkinter as tk
import cv2

window = tk.Tk()
window.title("OpenCV SelectROI")

canvas = tk.Canvas(window, width=640, height=480)
canvas.pack()

cap = cv2.VideoCapture(0)

def select_roi(event):
    x, y = event.x, event.y
    roi = cv2.selectROI(frame, fromCenter=False, showCrosshair=True)
    cv2.destroyAllWindows()
    cap.release()
    window.destroy()

canvas.bind("<Button 1>", select_roi)

while True:
    ret, frame = cap.read()
    if not ret:
        break
    frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
    img = Image.fromarray(frame)
    img = ImageTk.PhotoImage(image=img)
    canvas.create_image(0, 0, anchor=tk.NW, image=img)
    window.update()

window.mainloop()