python - cv2.setMouseCallback() 的参数应该是什么

Question

我一直在研究 opencv 并通过了 cv2.setMouseCallback() 。以下是鼠标点击画圆的代码。
导入cv2 将 numpy 导入为 np

def draw_circle(event,x,y,flags,param):
if event == cv2.EVENT_LBUTTONDBLCLK:
    cv2.circle(image,(x,y),(100,100),(255,0,0),-1)
img = np.zeros((512,512,3), np.uint8)
cv2.namedWindow("image")
cv2.setMouseCallback("image",draw_circle)

while True:
    cv2.imshow("image",image)
    if cv2.waitKey(1) & 0xFF == ord("q"):
        break
cv2.destroyAllWindows()`

请解释

1. 如何在不传递所有参数的情况下调用函数 draw_circle
2. 函数有五个参数，只有两个变量可以赋值
3. 创建 cv2.namedWindow("image") 的目的是什么

谢谢!

Answer 1

1. 你不调用draw_circle , openCV 将在具有适当事件和坐标的鼠标事件上为您调用它，您只需在 setMouseCallback 中指定要为哪个窗口调用哪个函数即可。

2. 如果您需要额外的变量，您可以通过 param 发送它们

3. 您可以有多个窗口，每个窗口具有不同的鼠标操作集

我希望这个例子能对偶然发现的人有所帮助:

import cv2
import numpy as np
from math import sqrt

def calc_distance(p1, p2):
    (x1, y1) = p1
    (x2, y2) = p2
    return round(sqrt((x1-x2)**2 + (y1-y2)**2))

# param contains the center and the color of the circle 
def draw_red_circle(event, x, y, flags, param):
    if event == cv2.EVENT_LBUTTONDBLCLK:
        center = param[0]
        radius = calc_distance((x, y), center)
        cv2.circle(img, center, radius, param[1], 2)


def draw_blue_circle(event, x, y, flags, param):
    if event == cv2.EVENT_LBUTTONDBLCLK:
        center = (100,100)
        radius = calc_distance((x, y), center)     
        cv2.circle(img, center, radius, (255, 0, 0), 2)

img = np.zeros((512,512,3), np.uint8)

# create 2 windows
cv2.namedWindow("img_red")
cv2.namedWindow("img_blue")

# different doubleClick action for each window
# you can send center and color to draw_red_circle via param
param = [(200,200),(0,0,255)]
cv2.setMouseCallback("img_red", draw_red_circle, param)
cv2.setMouseCallback("img_blue", draw_blue_circle) # param = None


while True:
    # both windows are displaying the same img
    cv2.imshow("img_red", img)
    cv2.imshow("img_blue", img)
    if cv2.waitKey(1) & 0xFF == ord("q"):
        break
cv2.destroyAllWindows()