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Preview USB Camera Image

This section explains how to preview live images from a USB camera using OpenCV in Python.

Previewing a USB camera stream is commonly used for: - Camera validation and debugging - Live image inspection - Verifying camera device indexing on Linux systems

1. Implementation Principle​

Use the cv2.VideoCapture() function to capture video streams from a USB camera device.

cv2.VideoCapture(device_index)
  • device_index is usually 0 for /dev/video0
  • Use 1, 2, etc. for additional connected cameras

2. Implementation Effect​

Navigate to the OpenCV working directory:

cd ~/opencv

Run the USB camera preview script:

python3 17.camera_preview_usb.py
note

The program opens video0 by default. To open other cameras, modify the device index in the code.

Select the camera preview window and press q to exit the program.

USB Camera Preview Result

3. Implementation Code​

import cv2

def preview_usb_camera():
    cap = cv2.VideoCapture(0)

    if not cap.isOpened():
        print("Error: Could not open USB camera.")
        return

    while True:
        ret, frame = cap.read()
        if not ret:
            break

        cv2.imshow(
            'USB Camera Preview',
            cv2.resize(frame, (640, 480))
        )

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

    cap.release()
    cv2.destroyAllWindows()

preview_usb_camera()

4. Code Explanation​

  • cv2.VideoCapture(0) opens /dev/video0
  • cap.read() captures a frame
  • cv2.imshow() displays the live stream
  • cv2.waitKey(1) listens for keyboard input
  • cap.release() releases the camera

Maintained by HemiHex for OpenCV-based image processing workflows.