def setHistogram(self, histogram):
super(TrackingHistogramWidget, self).setHistogram(histogram)
if not self.nodeItem:
self.nodeItem = TrackingNodeItem()
self.scene().addItem(self.nodeItem)
self.nodeItem.setHistogramItem(self._histogramItem)
self.nodeItem.setPos(QPoint(0, 0))
self.nodeItem.setZValue(300)
