How to change saturation and value using slider qcolor?

Question

Can someone help me make two sliders named brightness and saturation for changing both brightness and saturation, I set up a dialog with QLabel for displaying image and two sliders below. I tried converting my image to HSV then change S and V. But that does not work.

void Dialog::sliderchange(QLabel *label,int value){
QImage image=label->pixmap()->toImage();
for(int i=0;i<image.width();i++){
    for(int j=0;j<image.height();j++){
        QColor color=image.pixelColor(i,j);
        color.convertTo(QColor::Hsv);
        value=color.value();
        color.setHsv(color.hue(),color.saturation(),value);

    }
}
}

void Dialog::on_brightness_valueChanged(int value){
  sliderchange(ui->label,value);
}