如何使用OpenCV为画面中所有蓝色物体绘制外接矩形？

架构老林

2026-9-24

问题原因

现有代码仅能标注最大蓝色物体，是因为代码使用max(bluecnts, key=cv2.contourArea)仅提取了所有蓝色轮廓中面积最大的单个轮廓进行处理。要实现所有蓝色物体的外接矩形标注，只需遍历全部检测到的轮廓即可。

修改后的完整代码

import numpy as np
import cv2  

cap = cv2.VideoCapture(0)

while True:
    _, frame = cap.read()
    # Convert BGR to HSV
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
    # define range of blue color in HSV
    lower_blue = np.array([100,50,50])
    upper_blue = np.array([130,255,255])
    # Threshold the HSV image to get only blue colors
    mask = cv2.inRange (hsv, lower_blue, upper_blue)
    bluecnts = cv2.findContours(mask.copy(),
                              cv2.RETR_EXTERNAL,
                              cv2.CHAIN_APPROX_SIMPLE)[-2]


    if len(bluecnts)>0:
        # 遍历所有检测到的蓝色轮廓
        for cnt in bluecnts:
            # 过滤面积过小的噪点，阈值可根据实际需求调整
            if cv2.contourArea(cnt) < 10:
                continue
            (xg,yg,wg,hg) = cv2.boundingRect(cnt)
            cv2.rectangle(frame,(xg,yg),(xg+wg, yg+hg),(0,255,0),2)

    result = cv2.bitwise_and(frame, frame, mask=mask)

    cv2.imshow('frame',frame)
    cv2.imshow('mask',mask)
    cv2.imshow('blue', result)

    if cv2.waitKey(1) == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()