当我尝试将图像拆分为多个部分以分别处理并计算每个图像中的白色像素数时出现错误？

Question

I'm not sure how I would go about doing this, here is what I have so far.

def camera_callback(self, rgb_msg):
   

    # Check frame counter
    if( self.frame_count % self.frame_skip != 0 ):
        self.frame_count += 1
        return
    self.frame_count = 1
    
    
    # Get the camera image and make a copy
    img = CvBridge().imgmsg_to_cv2(rgb_msg, "bgr8" )
    img_hsv=cv.cvtColor(img, cv.COLOR_BGR2HSV)
    img_gray=cv.cvtColor(img, cv.COLOR_BGR2GRAY)
    

    hsv_low=np.array([self.H_low,self.S_low,self.V_low], np.uint8)
    hsv_high=np.array([self.H_high,self.S_high,self.V_high], np.uint8)

    mask=cv.inRange(img_hsv, hsv_low, hsv_high)
    res=cv.bitwise_and(img, img, mask=mask)

    self.n1=res[0:480,   0:213]
    self.n2=res[0:480, 214:427]
    self.n3=res[0:480, 428:640]

    
    nnz1=cv.countNonZero(self.n1)
    nnz2=cv.countNonzero(self.n2)
    nnz3=cv.countNonzero(self.n3)

    if(nnz1>nnz2 and nnz1>nnz3):
            self.yaw_rate=.5
    elif(nnz2>nnz1 and nnz2>nnz3):
            self.yaw_rate=0
    elif(nnz3>nnz2 and nnz3>nnz1):
            self.yaw_rate=-.5 
    
    self.msg.angular.x=self.yaw_rate
    self.pub_twist.publish(self.msg)

    #print(mask.shape[0]," ",mask.shape[1])

    #cv.imshow("mask",mask)
    #cv.imshow("res", res)
    self.display_image("mask", mask,True)
    self.display_image("result",res, True)

The error I get when running it is

[ERROR] [1656360138.949456]: bad callback: <bound method LineFollowNode.camera_callback of < main .LineFollowNode object at 0x7f10c61a7b20>> Traceback (most recent call last): File "/opt/ros/noetic/lib/python3/dist-packages/rospy/topics.py", line 750, in _invoke_callback cb(msg) File "/home/student/catkin_ws/src/hw06_freeman/scripts/line_follow.py", line 130, in camera_callback nnz1=cv.countNonZero(self.n1) cv2.error: OpenCV(4.2.0) ../modules/core/src/count_non_zero.dispatch.cpp:124: error: (-215:Assertion failed) cn == 1 in function 'countNonZero'

Answer 1

You're trying to count non-zero pixels on a colored image. You cannot do this as it's only meant to function with greyscale images. You should be using img_gray instead of img with res