Как превратить картинку в черно-белую в qt?

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QPixmap pixmap("original_image.jpg");

QGraphicsScene scene;
QGraphicsPixmapItem item(pixmap);

QGraphicsPixmapItem *bw_item = scene.addPixmap(pixmap);
QGraphicsBlurEffect *filter = new QGraphicsBlurEffect();
filter->setBlurRadius(0);
filter->setEnabled(true);
bw_item->setGraphicsEffect(filter);

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QPixmap pixmap("original_image.jpg");

QImage image = pixmap.toImage();

for(int y=0; y<image.height(); y++)
{
    for(int x=0; x<image.width(); x++)
    {
        QRgb pixel = image.pixel(x,y);
        int gray = qGray(pixel);
        image.setPixel(x,y,qRgb(gray,gray,gray));
    }
}

QPixmap blackWhitePixmap = QPixmap::fromImage(image);

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QPixmap pixmap("original_image.jpg");

QImage image = pixmap.toImage();

for(int y=0; y<image.height(); y++)
{
    for(int x=0; x<image.width(); x++)
    {
        QRgb pixel = image.pixel(x,y);
        int gray = ((qRed(pixel)*0.3) + (qGreen(pixel)*0.59) + (qBlue(pixel)*0.11));
        image.setPixel(x,y,qRgb(gray,gray,gray));
    }
}

QPixmap blackWhitePixmap = QPixmap::fromImage(image);