修改pyqtgraph匯出檢視背景顏色

    def writeImage(self, fileName=None):
        if fileName is None:
            self.fileDialog = FileDialog()
            if PlotItem.lastFileDir is not None:
                self.fileDialog.setDirectory(PlotItem.lastFileDir)
            self.fileDialog.setFileMode(QtGui.QFileDialog.AnyFile)
            self.fileDialog.setAcceptMode(QtGui.QFileDialog.AcceptSave) 
            self.fileDialog.show()
            self.fileDialog.fileSelected.connect(self.writeImage)
            return
        #if fileName is None:
            #fileName = QtGui.QFileDialog.getSaveFileName()
        if isinstance(fileName, tuple):
            raise Exception("Not implemented yet..")
        fileName = str(fileName)
        PlotItem.lastFileDir = os.path.dirname(fileName)
        self.png = QtGui.QImage(int(self.size().width()), int(self.size().height()), QtGui.QImage.Format_ARGB32)
        painter = QtGui.QPainter(self.png)
        painter.setRenderHints(painter.Antialiasing | painter.TextAntialiasing)

        #修改brush
        brush = QtGui.QBrush(QtGui.QColor("white"))
        painter.setBrush(brush)
        self.scene().render(painter, QtCore.QRectF(), self.mapRectToScene(self.boundingRect()))
        painter.end()
        self.png.save(fileName)