Efficient way of displaying a continuous stream of QImages

Question

I am currently using a QLabel to do this, but this seems to be rather slow:

void Widget::sl_updateLiveStreamLabel(spImageHolder_t _imageHolderShPtr) //slot         


        

Answer 1

QPixmap::fromImage is not the only problem. Using QPixmap::scaled or QImage::scaled also should be avoided. However you can't display QImage directly in QLabel or QGraphicsView. Here is my class that display QImage directly and scales it to the size of the widget:

Header:

class ImageDisplay : public QWidget {
  Q_OBJECT
public:
  ImageDisplay(QWidget* parent = 0);
  void setImage(QImage* image);

private:
  QImage* m_image;

protected:
  void paintEvent(QPaintEvent* event);

};

Source:

ImageDisplay::ImageDisplay(QWidget *parent) : QWidget(parent) {
  m_image = 0;
  setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
}

void ImageDisplay::setImage(QImage *image) {
  m_image = image;
  repaint();
}

void ImageDisplay::paintEvent(QPaintEvent*) {
  if (!m_image) { return; }
  QPainter painter(this);
  painter.drawImage(rect(), *m_image, m_image->rect());
}

I tested it on 3000x3000 image scaled down to 600x600 size. It gives 40 FPS, while QLabel and QGraphicsView (even with fast image transformation enabled) gives 15 FPS.