图片坐标和数组下标是相反的，坐标原点位于左上角
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,(row, col), 5, (0,255,0), -1) cv2.imwrite("square_circle_opencv.jpg", img)
