class ImageViewer(QtWidgets.QMainWindow):
    def __init__(self):
        super(ImageViewer, self).__init__()

        self.scene = QtWidgets.QGraphicsScene()
        self.imageLabel = QtWidgets.QLabel()
        self.cropLabel = QtWidgets.QLabel()
        self.scrollArea = QtWidgets.QScrollArea()
        self.scrollArea.setWidget(self.imageLabel)
        self.setCentralWidget(widget)

        self.scene.addWidget(splitter)
        self.view = QtWidgets.QGraphicsView(self.scene)
        self.view.setMouseTracking(True)
        self.view.setDragMode(QtWidgets.QGraphicsView.RubberBandDrag)

def mousePressEvent(self, eventQMouseEvent):
    print("pressed")
    self.originQPoint = self.view.mapToScene(eventQMouseEvent.pos())
    self.currentQRubberBand = QtWidgets.QRubberBand(QtWidgets.QRubberBand.Rectangle, self)
    self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, QtCore.QSize()))
    self.currentQRubberBand.show()

def mouseMoveEvent(self, eventQMouseEvent):
    self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, eventQMouseEvent.pos()).normalized())

def mouseReleaseEvent (self, eventQMouseEvent):
    #self.currentQRubberBand.hide()
    currentQRect = self.currentQRubberBand.geometry()
    print(currentQRect)
    self.currentQRubberBand.deleteLater()
    cropPixmap = self.pixmap.copy(currentQRect)
    self.cropLabel.setPixmap(cropPixmap)
    cropPixmap.save('output.png')