[Python] Can't show Cv2 frame in pyqt6 QLabel pixmap

I am trying to show a video feed from a camera captured using cv2 in a PyQt6 window. I have done some experimenting and followed a few guides to create the code included below. It creates the window in question and includes the camera text label but nothing shows up in the label with the pixmap applied.

import cv2
import numpy as np
from PyQt6.QtCore import Qt, QThread, pyqtSignal, pyqtSlot
from PyQt6.QtGui import QImage, QPixmap
from PyQt6.QtWidgets import QGridLayout, QLabel, QWidget


#Creates Thread to hold video updating to ensure other GUI operations can still run
class VideoThread(QThread):
#Declares Signal linked to ndarray
update_frame_signal = pyqtSignal(np.ndarray)

def __init__(self, index:int = 0):
#Adds Camera Index for use in later steps
super().__init__()
self.index = index

#When Thread is run loads a video feed from specified index and then if there is a new frame emits the above signal with the frame associated
def run(self):
self.is_running=True
camera = cv2.VideoCapture(self.index)
while self.is_running:
has_new_frame, frame = camera.read()
if has_new_frame:
self.update_frame_signal.emit(frame)

def stop(self):
self.is_running=False
self.quit()
self.terminate()

class CameraFeed(QWidget):
def __init__(self, index:int):
super().__init__()
self.image_width = 640
self.image_height = 480
self.index = index
label = "Camera " + str(index)
self.camera_frame = QLabel(self)
self.camera_label = QLabel(label)

#Adds the camera feed and the index number to the layout one above the other.
layout = QGridLayout()
layout.addWidget(self.camera_frame,0,0)
layout.addWidget(self.camera_label,1,0)
self.setLayout(layout)

#Create the instance of the thread, connect it to the update image function below and then start it
self.thread = VideoThread(self.index)
self.thread.update_frame_signal.connect(self.updateFrame)
self.thread.start()

def closeEvent(self, event):
#Ensures that the camera properly closes when the app exits
self.thread.stop()
event.accept()

@pyqtSlot(np.ndarray)
def updateFrame(self, cv2_img):
#This updates the frame shown on the QLabel with a new one from the cv2 camera after first converting it into an appropriate format for pyqt
qt_img = self.convertCv2Qt(cv2_img)
self.camera_frame.setPixmap(qt_img)


def convertCv2Qt(self, cv2_img):
#Converts the image from cv2 format to qt format
rgb_img = cv2.cvtColor(cv2_img, cv2.COLOR_BGR2RGB)
height, width, channels = rgb_img.shape #Gets Array properties
bytes_per_line = channels * width
qt_format = QImage(rgb_img.data, width, height, bytes_per_line, QImage.Format.Format_RGB888) #Formats as QImage
pixmap = qt_format.scaled(self.image_width, self.image_height, Qt.AspectRatioMode.KeepAspectRatio) #Scales to the specified size
return QPixmap.fromImage(pixmap) #Creates pixmap to apply to label





if __name__ == "__main__":
import sys

from PyQt6.QtWidgets import QApplication, QMainWindow

app = QApplication(sys.argv)

window = QMainWindow()
window.setWindowTitle("Camera Test")
window.setCentralWidget(CameraFeed(0))
window.show()

sys.exit(app.exec())



I have used a simpler block of code that excludes pyqt6 to just load the camera into a cv2 window to verify that the camera works and have successfully seen the image and confirmed that the camera works. However for the rest of the project I am planning I need it to display in my qt application.

Continue reading...