Free memory - QPixmap::grabWindow?

[hakermania]

I use this code in order to capture the color of a pixel, compare it with a HTML value and do an action if the comparisono is successful

while(1){
        sleep(3000);
        QPixmap *a = new QPixmap;
        *a = QPixmap::grabWindow(QApplication::desktop()->winId());
        QImage *img = new QImage;
        *img = a->toImage();
        QRgb b = img->pixel(796,554);
        QColor *c = new QColor;
        c->setRgb(b);
        qDebug() << c->name();
        delete a;
        delete c;
        if(c->name() == "#968d82"){
            system("canberra-gtk-play -f ~/Documents/Alert.wav");
        }

while(1){
        sleep(3000);
        QPixmap *a = new QPixmap;
        *a = QPixmap::grabWindow(QApplication::desktop()->winId());
        QImage *img = new QImage;
        *img = a->toImage();
        QRgb b = img->pixel(796,554);
        QColor *c = new QColor;
        c->setRgb(b);
        qDebug() << c->name();
        delete a;
        delete c;
        if(c->name() == "#968d82"){
            system("canberra-gtk-play -f ~/Documents/Alert.wav");
        }

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Every time it goes through the loop the program takes almost 4MB of memory usage
It's probaly because it grubs the whole desktop picture every time it runs...
I tried to free some by deleting 'a' and 'c' but it didn't work. Any suggestion?