Cannot save an indexed image from binary data as JPEG

#include <QtCore>
#include <QtGui>

int main(int argc, char **argv)
{
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
    QGuiApplication app(argc, argv);
#else
    QApplication app(argc, argv);
#endif

    QFile file("data.bin");

    if(!file.open(QFile::ReadOnly))
        qFatal("Cannot open file: %s", qPrintable(file.errorString()));

    QByteArray ba = file.readAll();

    QImage::Format format = QImage::Format_Indexed8;
    QVector<QRgb> table;

    for(int i = 0;i < 255;i++)
        table.append(qRgb(i, i, i));

    QImage image(reinterpret_cast<const uchar *>(ba.constData()),
                850,
                1400,
                850,
                format);

    if(image.isNull())
        qFatal("Image is null");

    image.setColorTable(table);

    //
    // Workaround:
    //
    // if(!image.convertToFormat(QImage::Format_RGB32).save("qt.jpg"))
    //    qFatal("Cannot save JPEG");
    //

    if(!image.save("qt.jpg"))
        qFatal("Cannot save JPEG");

    if(!image.save("qt.png"))
        qFatal("Cannot save PNG");

    qDebug("Success");

    return 0;
}