I am trying to run this face tracking program provided here, but running the python program returns;

Traceback (most recent call last):
  File "C:\Users\User\Desktop\Projects\Face Tracking\servo\face.py", line 27, in <module>
    cv2.resizeWindow('img', 500,500)
cv2.error: OpenCV(4.5.5) D:\a\opencv-python\opencv-python\opencv\modules\highgui\src\window_w32.cpp:1473: error: (-27:Null pointer) NULL window: 'img' in function 'cvResizeWindow'

I installed OpenCV with this command: python3 -m pip install opencv-python.

Here is the full code.

"""
   *Face Tracking System Using Arduino - Python Code*
    Close the Arduino IDE before running this code to avoid Serial conflicts.
    Replace 'COM5' with the name of port where you arduino is connected.
    To find the port check Arduino IDE >> Tools >> port.
    Upload the Arduino code before executing this code.

    # Code by Harsh Dethe, 09 Sep 2018 #
"""
import numpy as np
import serial
import time
import sys
import cv2

arduino = serial.Serial('COM3', 9600)
time.sleep(2)
print("Connection to arduino...")


face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')

cap = cv2.VideoCapture(0)

while 1:
    ret, img = cap.read()
    cv2.resizeWindow('img', 500,500)
    cv2.line(img,(500,250),(0,250),(0,255,0),1)
    cv2.line(img,(250,0),(250,500),(0,255,0),1)
    cv2.circle(img, (250, 250), 5, (255, 255, 255), -1)
    gray  = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    faces = face_cascade.detectMultiScale(gray, 1.3)

    for (x,y,w,h) in faces:
        cv2.rectangle(img,(x,y),(x w,y h),(0,255,0),5)
        roi_gray  = gray[y:y h, x:x w]
        roi_color = img[y:y h, x:x w]

        arr = {y:y h, x:x w}
        print (arr)
        
        print ('X :'  str(x))
        print ('Y :' str(y))
        print ('x w :'  str(x w))
        print ('y h :'  str(y h))

        xx = int(x (x h))/2
        yy = int(y (y w))/2

        print (xx)
        print (yy)

        center = (xx,yy)

        print("Center of Rectangle is :", center)
        data = "X{0:d}Y{1:d}Z".format(xx, yy)
        print ("output = '"  data  "'")
        arduino.write(data)
    

    cv2.imshow('img',img)
   
    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break

CodePudding user response：

Check this one hope it will work !

   """
   *Face Tracking System Using Arduino - Python Code*
    Close the Arduino IDE before running this code to avoid Serial conflicts.
    Replace 'COM5' with the name of port where you arduino is connected.
    To find the port check Arduino IDE >> Tools >> port.
    Upload the Arduino code before executing this code.

    # Code by Harsh Dethe, 09 Sep 2018 #
"""
import numpy as np
import serial
import time
import sys
import cv2

arduino = serial.Serial('COM3', 9600)
time.sleep(2)
print("Connection to arduino...")


face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')

cap = cv2.VideoCapture(0)

while 1:
    ret, img = cap.read()
    if ret == True:
        cv2.namedWindow("img", cv2.WINDOW_NORMAL)
        cv2.resizeWindow('img', 500, 500)
        cv2.line(img, (500, 250), (0, 250), (0, 255, 0), 1)
        cv2.line(img, (250, 0), (250, 500), (0, 255, 0), 1)
        cv2.circle(img, (250, 250), 5, (255, 255, 255), -1)
        gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
        faces = face_cascade.detectMultiScale(gray, 1.3)

        for (x, y, w, h) in faces:
            cv2.rectangle(img, (x, y), (x w, y h), (0, 255, 0), 5)
            roi_gray = gray[y:y h, x:x w]
            roi_color = img[y:y h, x:x w]

            arr = {y: y h, x: x w}
            print(arr)

            print('X :'   str(x))
            print('Y :' str(y))
            print('x w :'   str(x w))
            print('y h :'   str(y h))

            xx = int(x (x h))/2
            yy = int(y (y w))/2

            print(xx)
            print(yy)

            center = (xx, yy)

            print("Center of Rectangle is :", center)
            data = "X{0:d}Y{1:d}Z".format(xx, yy)
            print("output = '"   data   "'")
            arduino.write(data)

        cv2.imshow('img', img)

        k = cv2.waitKey(30) & 0xff
        if k == 27:
            break
    else:
        break

CodePudding user response：

The error is:

error: (-27:Null pointer) NULL window: 'img' in function 'cvResizeWindow'

And that means the given window doesn't exist (yet).

You should have created that window first, using createWindow or imshow.

A window isn't an image. A string containing the name of something ("img") isn't the thing (img). If you wanted to resize() an image, you used the wrong function.

CodePudding user response：

Easier way to do this. Always used nameWindowbefore while condition block. It is practical way, to prevent an error.

# Naming a window
cv2.namedWindow("img", cv2.WINDOW_NORMAL)
while 1:
    ret, img = cap.read()
    cv2.resizeWindow('img', 500,500)