QImage corrupts with OpenCV [duplicate] - c++

Question

This question already has answers here:
cv::Mat to QImage and back
(2 answers)
Closed 1 year ago.
I have a webcam demo with Qt and OpenCV. Basically it will show the webcam's feed, and when a button gets clicked, it starts a thread with a long (three-five seconds) thread.
The problem is that the QImage gets immediately corrupted as you can see here when I click the button, and I don't see the video feed anymore. The signals & slots work (I see the output in the console), but I cannot spot the problem here.
Can anyone help?
window::window() : QMainWindow(NULL, 0)
{
std::cout << "constructor start" << std::endl;
setWindowTitle("Video");
button = new QPushButton("Long Job");
connect(button, SIGNAL(clicked()), this, SLOT(longjob()));
image = new QLabel();
image->setAlignment(Qt::AlignCenter);
layout = new QVBoxLayout();
layout->addWidget(image);
layout->addWidget(button);
mainwidget = new QWidget();
mainwidget->setLayout(layout);
resize(800, 600);
setCentralWidget(mainwidget);
cap = cv::VideoCapture(0);
timer = new QTimer();
timer->setInterval(100);
timer->start();
connect(timer, SIGNAL(timeout()), this, SLOT(newframe()));
std::cout << "constructor end" << std::endl;
}
void window::newframe()
{
std::cout << "FRAME " << count++ << std::endl;
cv::Mat frame;
cap >> frame;
image->setPixmap(QPixmap::fromImage(showImage(frame))); // converts perfectly
}
void window::longjob()
{
std::cout << "START THREAD" << std::endl;
w = new worker();
connect(w, SIGNAL(resultReady(double)), this, SLOT(detected(double)));
w->start();
return;
}
void window::detected(double d)
{
disconnect(w, SIGNAL(resultReady(double)), this, SLOT(detected(double)));
std::cout << "DETECTED " << d << std::endl;
delete w;
frames.clear();
}
class worker : public QThread
{
Q_OBJECT
public:
worker();
~worker();
void run() Q_DECL_OVERRIDE;
signals:
void resultReady(double d);
};
worker::worker() : QThread()
{
}
worker::~worker()
{
std::cout << "THREAD EXIT" << std::endl;
}
void worker::run()
{
std::cout << "THREAD RUN" << std::endl;
double d = longOpenCVJob();
emit resultReady(d);
}

Answer 1

I would use this code for showImage():
QImage window::showImage(cv::Mat mat)
{
cv::Mat tmp;
mat.convertTo(tmp, CV_8U);
cvtColor(tmp, tmp, CV_BGR2RGB);
QImage img = QImage((const unsigned char *)(tmp.data), tmp.cols, tmp.rows, tmp.step, QImage::Format_RGB888);
return img;
}