From mainwindow i'm opening a dialog writing:
SplashScreenDialog *splScrDlg = new SplashScreenDialog(this);
splScrDlg->show();

I'm opening and showing an image [for splash screen] writing
QPalette palette;
QPixmap pixMap("army.jpg");
QSize size(this->height(), this->width());
QPixmap pixMapScaled(pixMap.scaled(size));
palette.setBrush(QPalette::Background, pixMapScaled);
this->setPalette(palette);

Now i want to control the opacity[or transparency] of this image, i wan to make it transparent as time goes by[an splash screen behaviour].

How to do it ?