How to scale QImage to a small size with good quality

Question

I have eight different videos. And I am trying to show these videos in a split window. My video quality is 720p. But I need to fit in small frame. When I resize the video with p = convert_to_Qt_format.scaled(256, 450, Qt.KeepAspectRatio) as a 256x450 I couldn't get good quality of video. How can I resize as a good quality. What is your suggestion to me?

@pyqtSlot(list)
    def update_image(self, cv_img = []):
        """Updates the image_label with a new opencv image"""
        qt_img = []
        for i in range(0,8):
            # qt_img.append(0)
            qt_img.append(self.convert_cv_qt(cv_img[i]))
        self.ui.video1.setPixmap(qt_img[0])
        self.ui.video2.setPixmap(qt_img[1])
        self.ui.video3.setPixmap(qt_img[2])
        self.ui.video4.setPixmap(qt_img[3])
        self.ui.video5.setPixmap(qt_img[4])
        self.ui.video6.setPixmap(qt_img[5])
        self.ui.video7.setPixmap(qt_img[6])
        self.ui.video8.setPixmap(qt_img[7])

    def convert_cv_qt(self, cv_img):
        """Convert from an opencv image to QPixmap"""
        rgb_image = cv2.cvtColor(cv_img, cv2.COLOR_BGR2RGB)
        h, w, ch = rgb_image.shape
        bytes_per_line = ch * w
        convert_to_Qt_format = QtGui.QImage(rgb_image.data, w, h, bytes_per_line, QtGui.QImage.Format_RGB888)
        p = convert_to_Qt_format.scaled(256, 450, Qt.KeepAspectRatio)
        return QPixmap.fromImage(p)

Answer 1

Note that QImage::scaled() has an optional parameter transformMode that defaults to Qt::FastTransformation. If you pass Qt::SmoothTransformation the results should be better, because bilinear filtering is used.