How do I access my USB camera using OpenCV with python?

Question

I am having trouble accessing my USB camera using OpenCV with python.

I get the following error message which I understand means no frame was captured?

error: OpenCV(3.4.1) C:\Miniconda3\conda-bld\opencv-suite_1533128839831\work\modules\highgui\src\window.cpp:356: error: (-215) size.width>0 && size.height>0 in function cv::imshow

My camera is the following: https://www.gophotonics.com/products/scientific-industrial-cameras/point-grey-research-inc/45-571-cm3-u3-50s5m-cs

Simple code as below. Any thoughts? Some help I'll appreciate

import numpy as np
import cv2

cap = cv2.VideoCapture(0)
while(True):
    ret, frame = cap.read()

    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

Answer 1

The camera index most of the time is 0 as default with computers which come with an integrated camera, but if you're plugging a USB camera, its camera index could be 1 or 2, you can try with both of them.

But if you wanna get all camera index available, you can use the following simple script to find out:

import cv2
import numpy as np

all_camera_idx_available = []

for camera_idx in range(10):
    cap = cv2.VideoCapture(camera_idx)
    if cap.isOpened():
        print(f'Camera index available: {camera_idx}')
        all_camera_idx_available.append(camera_idx)
        cap.release()

The result would be a list like: [0,1,2,...] with all camera index available.

But if you're using a USB camera you have to keep in mind that some OpenCV functions won't work, take a look at this.