C++ (Qt5.5) expend image Viewer example by save function

Question

I expanded the Qt Imageviewer example by some functionality. I basically want to add a save function. In this example there are two functions of the same class handling the picture open process:

void ImageViewer::open()
{
    QStringList mimeTypeFilters;
    foreach (const QByteArray &mimeTypeName, QImageReader::supportedMimeTypes())
        mimeTypeFilters.append(mimeTypeName);
    mimeTypeFilters.sort();
    const QStringList picturesLocations = QStandardPaths::standardLocations(QStandardPaths::PicturesLocation);
    QFileDialog dialog(this, tr("Open File"),
                       picturesLocations.isEmpty() ? QDir::currentPath() : picturesLocations.last());
    dialog.setAcceptMode(QFileDialog::AcceptOpen);
    dialog.setMimeTypeFilters(mimeTypeFilters);
    dialog.selectMimeTypeFilter("image/jpeg");

    while (dialog.exec() == QDialog::Accepted && !loadFile(dialog.selectedFiles().first())) {}
}

and

bool ImageViewer::loadFile(const QString &fileName)
{
    QImageReader reader(fileName);
    reader.setAutoTransform(true);
    const QImage image = reader.read();
    if (image.isNull()) {
        QMessageBox::information(this, QGuiApplication::applicationDisplayName(),
                                 tr("Cannot load %1.").arg(QDir::toNativeSeparators(fileName)));
        setWindowFilePath(QString());
        imageLabel->setPixmap(QPixmap());
        imageLabel->adjustSize();
        return false;
}
    imageLabel->setPixmap(QPixmap::fromImage(image));
    scaleFactor = 1.0;

    printAct->setEnabled(true);
    fitToWindowAct->setEnabled(true);
    convAct->setEnabled(true); // so the image can be converted if it was loaded ...
    updateActions();

    if (!fitToWindowAct->isChecked()) {
        imageLabel->adjustSize();
    }
    setWindowFilePath(fileName);
    return true;
    }

So I added a save button in the menus, and in the ImageViewer.h class:

class ImageViewer : public QMainWindow
{
    Q_OBJECT

public:
    ImageViewer();
    bool loadFile(const QString &);

private slots:
    void open();
    void print();
    void save();  // <--- 

Everything is fine, but I don't know how to get my Image in the new function, besides the fact, that I obviously make a wrong conversion from QPixmap to QImage - but I also tried replacing it with QPixmap test = imageLabel->pixmap() without any success.

void ImageViewer::save()
{
    QImage test = imageLabel->pixmap();
    qWarning()<< test;
    QByteArray bytes;
    QBuffer buffer(&bytes);
    buffer.open(QIODevice::WriteOnly);
    image.save(&buffer, "BMP");
    QString monobitmap = QString::fromLatin1(bytes.toBase64().data());
}   

In the end, I want to save it as a monochrome bitmap (no matter what it was before). Sorry for posting a lot of code.

Answer 1

It sounds like your problem is that you have a QPixmap object and you need a QImage object. If that's the case, then you can convert a QPixmap into a QImage by calling the toImage() method on the QPixmap; it will return the resulting QImage object.

As for you converting the QImage to a monochrome bitmap, you should be able to do that by calling convertToFormat(QImage::Format_Mono) on your QImage. That call will return the new (1-bit) version of the QImage.