错误：在 Python - OPENCV（Pycharm）中同时打开两个摄像头 - 错误（-215：断言失败）._src:empty() in ZC1C425268E68385D1AB5Z'cv:17cvtColor4'cv:17385D1AB5Z'7

Question

happy day, I am trying to synchronize two cameras (my local computer) and the camera of my cell phone with IP Web cam, however when running the code it generates an error and the two cameras that I have previously opened are closed (see photo ). What would this be due to? Thanks for your help!

ERROR -->

Traceback (most recent call last):
   File "C:\Users\JUCABALL\Desktop\camera_stream_openCV-master\main.py", line 20, in <module>
     cv2.imshow ('cam1', frame1)
cv2.error: OpenCV (4.5.4-dev) D:\a\opencv-python\opencv-python\opencv\modules\imgproc\src\color.cpp: 182:
error: (-215: Assertion failed)! _src .empty () in function 'cv :: cvtColor'

This is the tabs - after fews seconds tabs close

[Tabs, 2 cameras][1]

This is my code

import numpy as np
import cv2


# capture the webcam
vid1 = cv2.VideoCapture(0, cv2.CAP_DSHOW)
vid2 = cv2.VideoCapture(1, cv2.CAP_DSHOW)
vid3 = cv2.VideoCapture(
    "http://192.168.0.11:8080/video", cv2.CAP_DSHOW
)  # ipwebcam address


while True:  # while true, read the camera
    ret, frame = vid1.read()
    ret1, frame1 = vid2.read()
    ret2, frame2 = vid3.read()

    if ret:
        cv2.imshow("cam0", frame)  # frame with name and variable of the camera
        cv2.imshow("cam1", frame1)
        cv2.imshow("cam3", frame2)

    # to break the loop and terminate the program
    if cv2.waitKey(1) & 0xFF == ord("q"):
        break

vid1.release()
vid2.release()
vid3.release()

Answer 1

The problem is you're not checking the value of ret1 and ret2 .

If those are False , the images will not have been captured, and you're still trying to show them, and OpenCV crashes because there's no way to show an image that doesn't exist.

Try

if ret:
    cv2.imshow("cam0", frame)
if ret1:
    cv2.imshow("cam1", frame1)
if ret2:
    cv2.imshow("cam3", frame2)  

instead.

You could also store all of the capture devices in a list, and all the captured images equally so, to make the code a little simpler to work with:

import numpy as np
import cv2

captures = [
    cv2.VideoCapture(0, cv2.CAP_DSHOW),
    cv2.VideoCapture(1, cv2.CAP_DSHOW),
    cv2.VideoCapture("http://192.168.0.11:8080/video", cv2.CAP_DSHOW),  # ipwebcam address
]


while True:  # while true, read the camera
    frames = []
    for cap in captures:
        ret, frame = cap.read()
        frames.append((frame if ret else None))

    for i, frame in enumerate(frames):
        if frame is not None:  # None if not captured
            cv2.imshow(f"cam{i}", frame)

    # to break the loop and terminate the program
    if cv2.waitKey(1) & 0xFF == ord("q"):
        break

for cap in captures:
    cap.release()