How to make screenshot while showing video from cam?

Question

#Importing necessary libraries, mainly the OpenCV, and PyQt libraries
import cv2
import numpy as np
import sys
from PyQt5 import QtCore
from PyQt5 import QtWidgets
from PyQt5 import QtGui
from PyQt5.QtCore import pyqtSignal

class ShowVideo(QtCore.QObject):

    #initiating the built in camera
    camera_port = -1
    camera = cv2.VideoCapture(camera_port)
    VideoSignal = QtCore.pyqtSignal(QtGui.QImage)

    def __init__(self, parent = None):
        super(ShowVideo, self).__init__(parent)

    @QtCore.pyqtSlot()
    def startVideo(self):
        run_video = True

        while run_video:
            ret, image = self.camera.read()

            color_swapped_image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
            height, width, _ = color_swapped_image.shape

            qt_image = QtGui.QImage(color_swapped_image.data,
                                    width, 
                                    height,
                                    color_swapped_image.strides[0],
                                    QtGui.QImage.Format_RGB888)

            pixmap = QtGui.QPixmap(qt_image)
            qt_image = pixmap.scaled(640, 480, QtCore.Qt.KeepAspectRatio)
            qt_image = QtGui.QImage(qt_image)

            self.VideoSignal.emit(qt_image)

    @QtCore.pyqtSlot()
    def makeScreenshot(self):
        #cv2.imwrite("test.jpg", self.image)
        print("Screenshot saved")
        #self.qt_image.save('test.jpg')

class ImageViewer(QtWidgets.QWidget):
    def __init__(self, parent = None):
        super(ImageViewer, self).__init__(parent)
        self.image = QtGui.QImage()
        self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)



    def paintEvent(self, event):
        painter = QtGui.QPainter(self)
        painter.drawImage(0,0, self.image)
        self.image = QtGui.QImage()

    def initUI(self):
        self.setWindowTitle('Test')


    @QtCore.pyqtSlot(QtGui.QImage)
    def setImage(self, image):
        if image.isNull():
            print("viewer dropped frame!")

        self.image = image
        if image.size() != self.size():
            self.setFixedSize(image.size())
        self.update()


if __name__ == '__main__':

    app = QtWidgets.QApplication(sys.argv)
    thread = QtCore.QThread()
    thread.start()

    vid = ShowVideo()
    vid.moveToThread(thread)
    image_viewer = ImageViewer()
    #image_viewer.resize(200,400)

    vid.VideoSignal.connect(image_viewer.setImage)

    #Button to start the videocapture:

    push_button = QtWidgets.QPushButton('Start')
    push_button.clicked.connect(vid.startVideo)
    push_button2 = QtWidgets.QPushButton('Screenshot')
    push_button2.clicked.connect(vid.makeScreenshot)
    vertical_layout = QtWidgets.QVBoxLayout()

    vertical_layout.addWidget(image_viewer)
    vertical_layout.addWidget(push_button)
    vertical_layout.addWidget(push_button2)

    layout_widget = QtWidgets.QWidget()
    layout_widget.setLayout(vertical_layout)

    main_window = QtWidgets.QMainWindow()
    main_window.setCentralWidget(layout_widget)
    main_window.resize(640,480)
    main_window.show()
    sys.exit(app.exec_())

This code showing video from camera in endless loop using OpenCV and PyQt5. But how to make screenshot and don't stop showing video. I think it needs to be stop loop for a little, make screnshot, and run loop again.

Answer 1

You can use cv2.waitKey() for the same, as shown below:

while run_video:
            ret, image = self.camera.read()

            if(cv2.waitKey(10) & 0xFF == ord('s')):
            cv2.imwrite("screenshot.jpg",image)

(I'm guessing that by the term "screenshot", you mean the camera frame, and not the image of the entire screen.) When you press 's' on the keyboard, it'll perform imwrite. Note that if you wish to save multiple images, you'd have to vary the filename. The above code will overwrite screenshot.jpg to save only the latest frame.