Python3.x 有没有办法使用 python opencv 计算与图像的白色距离

As you can see in the image, the size of the image is 2000*2000. We have to find the distance of the image from all the 4 coordinates. I am trying with opencv contours but on some other image it is not working.

image = cv2.imread(image_full_path)
ori_h, ori_w, _ = image.shape
print("Original height, width-->", ori_h, ori_w)
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)  # grayscale
_, thresh = cv2.threshold(gray, 150, 255, cv2.THRESH_BINARY_INV)  # threshold
kernel = cv2.getStructuringElement(cv2.MORPH_CROSS, (3, 3))
dilated = cv2.dilate(thresh, kernel, iterations=13)  # dilate
contours, hierarchy = cv2.findContours(dilated, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)  # get contours

idx = 0
# for each contour found, draw a rectangle around it on original image
# print('length', len(contours))
for contour in contours:
    idx += 1

    # get rectangle bounding contour
    [x, y, w, h] = cv2.boundingRect(contour)
    remaining_height_bottom = ori_h - (y + h)
    remaining_width_right_side = ori_w - (x + w)

    print("Upper Height, Right Width-->", y, x)
    print("Bottom Height, Left Width-->", remaining_height_bottom, remaining_width_right_side)
    print("Image Height, Image Width-->", h, w)

提前谢谢.如果有人认为提问的方式是错误的，请忽略.我真的需要帮助.