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()

Scrutiny

Try putting '1' instead of '0' in VideoCapture. Like, cv2.VideoCapture(1). – Pachyderm

Thanks for the reply. I do not think its an indexing problem, I have tried iterating up to index 500 and none work... – Scrutiny

Is your usb camera working normally with your computer, without trying to access it from python? Like using some default usb option to access it. Just to check if it's compatible and it works fine normally. – Pachyderm

It works using spinview, program provided by the company – Scrutiny

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.

Oxen

Thanks for the reply. I do not think its an indexing problem, I have tried iterating up to index 500 and none work... – Scrutiny

Answer 2

If the cameras you are using are spinnaker cameras, you have to use the PySpin camera API to get images off the device.

Check out this link to get this API installed. No module named 'PySpin'

Longevous