QLabel show Image problem

[chen.xu]

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

[VRonin]

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

[SGaist]

Hi and welcome to devnet,

At what speed are you triggering the timer ?