import cv2
import numpy as np

import os
os.environ['QT_QPA_PLATFORM_PLUGIN_PATH'] = r'path/to/qt/plugins/platforms'

def  maintain_aspect_ratio_resize(image,  width=None,  height=None,  inter=cv2.INTER_AREA):
     dim =  None
     (h, w)  = image.shape[:2]
     if width is  None  and height is  None:
        return image

     if width is  None:
        r = height /  float(h)
        dim =  (int(w * r), height)
     else:
        r = width /  float(w)
        dim =  (width,  int(h * r))

     return cv2.resize(image, dim,  interpolation=inter)

template = cv2.imread('testimg_circle.jpg')
template = cv2.cvtColor(template, cv2.COLOR_BGR2GRAY)
template = cv2.Canny(template,  50,  200)
(tH, tW)  = template.shape[:2]
cv2.imshow("template", template)

original_image = cv2.imread('test.png')
final = original_image.copy()
gray = cv2.cvtColor(original_image, cv2.COLOR_BGR2GRAY)
found =  None

for scale in np.linspace(0.2,  1.0,  20)[::-1]:
     resized = maintain_aspect_ratio_resize(gray,  width=int(gray.shape[1]  * scale))
     r = gray.shape[1]  /  float(resized.shape[1])

     if resized.shape[0]  < tH or resized.shape[1]  < tW:
        break
     canny = cv2.Canny(resized,  50,  200)
     detected = cv2.matchTemplate(canny, template, cv2.TM_CCOEFF)
     (_, max_val, _, max_loc)  = cv2.minMaxLoc(detected)

     if found is  None  or max_val > found[0]:
        found =  (max_val, max_loc, r)

(_, max_loc, r)  = found
(start_x, start_y)  =  (int(max_loc[0]  * r),  int(max_loc[1]  * r))
(end_x, end_y)  =  (int((max_loc[0]  + tW)  * r),  int((max_loc[1]  + tH)  * r))


cv2.rectangle(original_image,  (start_x, start_y),  (end_x, end_y),  (0,255,0),  2)
cv2.imshow('detected', original_image)

cv2.rectangle(final,  (start_x, start_y),  (end_x, end_y),  (255,255,255),  -1)
cv2.imwrite('final.png', final)
cv2.waitKey(0)