полукруг
import numpy as np
import cv2
my_img = np.zeros((400, 400, 3), dtype = "uint8")
# creating for rectangle
cv2.ellipse(my_img,(256,256),(100,50),0,0,180,255,-1)
cv2.imshow('Window', my_img)
# allows us to see image
# until closed forcefully
cv2.waitKey(0)
cv2.destroyAllWindows()
morancium