Why is OpenCV ROI not working?

Question

Python

I'm trying to select a region of interest in an image, but an empty array is returned. What am I doing wrong, and what values ​​should be specified to determine the region?
Here is the code:

import numpy as np
import cv2

img = cv2.imread("circ.jpg")
img = cv2.resize(img, (500, 500))

roi = img[100:100, 200:200]

print(roi)

Picture:

Answer 1

Because the image was cut from 100 to 100 pixels in y and from 200 to 200 in x
img[y:y+h, x:x+w]