Find point coordinates on image

Question

I've created random points and added a list these points double. Then I've drawn graphic and save as a image.

I'm able to draw a line from one point to another point with this code :

cv2.line(img=result,pt1=,pt2=,color=(0,255,255),thickness=5)

I'have a problem there . If I use plt.show() for graphic, I have all points coordinates in list. But when I save this graphic as a image and show with cv2 lib, then all points coordinates changes.

• How can I find these points coordinates on image ?

• For exapmle: On this graphic you can see (1,4) point. If I save this graphic as a image then this point gets a (104, 305) coordinates on image.

import numpy as np
import random
import matplotlib.pyplot as plt
import cv2

points = np.random.randint(0, 9, size=(18,2))
print(points)
plt.plot(points[:,0], points[:,1], '.',color='k')

plt.savefig("graphic.png",bbox_inches="tight")
result = cv2.imread("graphic.png")

cv2.imshow("Graphic",result)

Answer 1

I think you are confusing yourself.

• Your x,y coordinates start at bottom-left corner of image, have x coordinate first and assume the image is 9 pixels wide.

• OpenCV stores points relative to the top-left corner, have the y coordinate first and refer to an image hundreds of pixels wide.