draw a circle over image opencv

Question

Im usign python and opencv to get a image from the webcam, and I want to know how to draw a circle over my image, just a simple green circle with transparent fill

Answer 1

Just an additional information:

The parameter "center" of OpenCV's drawing function cv2.circle() takes a tuple of two integers. The first is the width location and the second is the height location. This ordering is different from the usual array indexing. The following example demonstrates the issue.

import numpy as np
import cv2

height, width = 150, 200
img = np.zeros((height, width, 3), np.uint8)
img[:, :] = [255, 255, 255]

# Pixel position to draw at
row, col = 20, 100

# Draw a square with position 20, 100 as the top left corner
for i in range(row, 30):
    for j in range(col, 110):
        img[i, j] = [0, 0, 255]

# Will the following draw a circle at (20, 100)?
# Ans: No. It will draw at row index 100 and column index 20.
cv2.circle(img,(col, row), 5, (0,255,0), -1)

cv2.imwrite("square_circle_opencv.jpg", img)