Display QImage with QtGui

Question

I am new to Qt, and I am trying to create a simple GUI Application that displays an image once a button has been clicked on.

I can read the image in a QImage object, but is there any simple way to call a Qt function that takes the QImage as an input, and displays it?

Answer 1

Simple, but complete example showing how to display QImage might look like this:

#include <QtGui/QApplication>
#include <QLabel>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QImage myImage;
    myImage.load("test.png");

    QLabel myLabel;
    myLabel.setPixmap(QPixmap::fromImage(myImage));

    myLabel.show();

    return a.exec();
}

Answer 2

Drawing an image using a QLabel seems like a bit of a kludge to me. With newer versions of Qt you can use a QGraphicsView widget. In Qt Creator, drag a Graphics View widget onto your UI and name it something (it is named mainImage in the code below). In mainwindow.h , add something like the following as private variables to your MainWindow class:

QGraphicsScene *scene;
QPixmap image;

Then just edit mainwindow.cpp and make the constructor something like this:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    image.load("myimage.png");
    scene = new QGraphicsScene(this);
    scene->addPixmap(image);
    scene->setSceneRect(image.rect());

    ui->mainImage->setScene(scene);
}

Answer 3

One common way is to add the image to a QLabel widget using QLabel::setPixmap() , and then display the QLabel as you would any other widget. Example:

#include <QtGui>

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  QPixmap pm("your-image.jpg");
  QLabel lbl;
  lbl.setPixmap(pm);
  lbl.show();
  return app.exec();
}

Answer 4

Thanks All, I found how to do it, which is the same as Dave and Sergey:

I am using QT Creator:

In the main GUI window create using the drag drop GUI and create label (eg "myLabel")

In the callback of the button (clicked) do the following using the (*ui) pointer to the user interface window:

void MainWindow::on_pushButton_clicked()
{
     QImage imageObject;
     imageObject.load(imagePath);
     ui->myLabel->setPixmap(QPixmap::fromImage(imageObject));

     //OR use the other way by setting the Pixmap directly

     QPixmap pixmapObject(imagePath");
     ui->myLabel2->setPixmap(pixmapObject);
}

Answer 5

As far as I know, QPixmap is used for displaying images and QImage for reading them. There are QPixmap::convertFromImage() and QPixmap::fromImage() functions to convert from QImage .