I do not understand your question.

I have a QPixmap that contains an image. is something like this

image.JPG

and I need to make zoom.

for this reason I put it in a QwtPlot, to use the function:

QwtPlotZoomer* zoomer = new MyZoomer(canvas());
zoomer->setMousePattern(QwtEventPattern::MouseSelect2,
Qt::RightButton, Qt::ControlModifier);
zoomer->setMousePattern(QwtEventPattern::MouseSelect3,
Qt::RightButton);