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QLabel show Image problem



  • I want to get image from opencv capture and show it on QLabel frame by frame. Now i use a timer to refresh ui

    this->timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(updatePicture()));
    
    void FaceCamera::updatePicture()
    {
    	cap >> this->image;
    	showMatOnQLabel(image, ui.cameraLabel);
    }
    
    void FaceCamera::showMatOnQLabel(cv::Mat mat, QLabel *qlabel)
    {
    	//conversion from Mat to QImage
    	if (mat.empty())
    		return;
    
    	cv::Mat dest;
    	cv::cvtColor(mat, dest, CV_BGR2RGB);
    
    	QImage imageFromMat = QImage((uchar*)dest.data, dest.cols, dest.rows, dest.step, QImage::Format_RGB888);
    	QImage qimage = imageFromMat.scaled(QSize(qlabel->width(), qlabel->height()), Qt::AspectRatioMode::KeepAspectRatio);
    
    	//show QImage using QLabel
    	qlabel->setPixmap(QPixmap::fromImage(qimage));
    }
    

    it can works, but if i directly get frame in main thread one by one and showMatOnQLabel,
    it will not show image util the last frame i get.

    why this happens ? plese help me

    thx : ]

    chen.xu
    from beijing
    2019.9.30



  • Try adding qlabel->repaint(); after qlabel->setPixmap


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    At what speed are you triggering the timer ?


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