Showing continuous stream of QImages - qt

Question

I have a set of QImages which come to a function (after a fixed interval of 4 seconds) and the function's job is to update the QLabel to show the new image.
While doing this, I can see a very obvious delay in the image rendering.
I had also followed the suggestions on the link:
Efficient way of displaying a continuous stream of QImages
But, even with using ImageDisplay in the link above, I can see a delay in image rendering.
Can anyone please suggest the best way to do this?
Below is the code.. The images required for the code to run are located at:
https://www.dropbox.com/sh/jiqdfqoiimjs7ei/AAAXezUeeCFyZXjNNOTmWZVga?dl=0
#include <QDialog>
#include <QtGui>
#include <QtCore>
#include <QApplication>
#include <QWidget>
#include <QImage>
class imageDisplay : public QWidget
{
public:
imageDisplay(QWidget*);
~imageDisplay();
void setImage(QImage* img);
private:
QImage* m_image;
protected:
void paintEvent(QPaintEvent* evt);
};
imageDisplay::imageDisplay(QWidget* parent) : QWidget(parent)
{
m_image = 0;
setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
}
imageDisplay::~imageDisplay()
{
}
void imageDisplay::setImage(QImage* img)
{
m_image = img;
repaint();
}
void imageDisplay::paintEvent(QPaintEvent*)
{
if(!m_image) return;
QPainter painter(this);
painter.drawImage(rect(), *m_image, m_image->rect());
}
////////////////////////////////////
//
int main(int arc, char ** argv)
{
QApplication theApp(arc, argv, true);
QDialog* dlg = new QDialog();
imageDisplay* wgt = new imageDisplay(dlg);
wgt->resize(600,400);
dlg->show();
for(int i = 0 ; i <= 19; ++i)
{
sleep(1);
QString fileName = "aaa" + QString::number(i) + ".png";
QImage* img = new QImage(fileName);
wgt->setImage(img);
}
return theApp.exec();
}