Simple PyQt4/OpenCV2 script which uses the Webcam

webcam_preview.py

import sys
import numpy
import cv2
from PyQt4.QtGui import QApplication, QWidget, QLabel, QGroupBox, QVBoxLayout, QImage, QPixmap
from PyQt4.QtCore import QSize, QTimer

# GUI code

app = QApplication(sys.argv)
window = QWidget()

videoPreviewGroupBox = QGroupBox("Look at your face !", window)
videoPreviewLabel = QLabel(videoPreviewGroupBox)
videoPreviewLabel.setMinimumSize(QSize(600, 480))

internLayout = QVBoxLayout(videoPreviewGroupBox)
videoPreviewGroupBox.setLayout(internLayout)
internLayout.addWidget(videoPreviewLabel)

layout = QVBoxLayout(window)
window.setLayout(layout)
layout.addWidget(videoPreviewGroupBox)
window.setWindowTitle('Webcam preview')

window.move(app.desktop().availableGeometry().center() - window.rect().center())  # Center the window
window.show()

# Webcam reading code

webcam = cv2.VideoCapture(0)  # Webcam is the first video capture device


def showCapture():
    success, frame = webcam.read()  # Get a picture from the webcam
    if success:
        rgb_frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)  # Convert (Blue,Green,Red) to (Red,Green,Blue)
        assert isinstance(rgb_frame, numpy.ndarray)  # An image is just a NumPy array
        image = QImage(rgb_frame.tobytes(),  # The content of the image
                       rgb_frame.shape[1],  # The width (number of columns)
                       rgb_frame.shape[0],  # The height (number of rows)
                       QImage.Format_RGB888)  # The image is stored in 3*8-bit format
        videoPreviewLabel.setPixmap(QPixmap.fromImage(image))  # Show the image


# Timer code

timer = QTimer(window)
timer.timeout.connect(showCapture)  # When timeout is reached, call showCapture
timer.start(40)  # Updates image every 40 milliseconds

sys.exit(app.exec())