def onCMapSave(self, event=None, col='int'):
        """save color table image"""
        file_choices = 'PNG (*.png)|*.png'
        ofile = 'Colormap.png'
        dlg = wx.FileDialog(self, message='Save Colormap as...',
                            defaultDir=os.getcwd(),
                            defaultFile=ofile,
                            wildcard=file_choices,
                            style=wx.FD_SAVE|wx.FD_CHANGE_DIR)

        if dlg.ShowModal() == wx.ID_OK:
            self.cmap_panels[0].cmap_canvas.print_figure(dlg.GetPath(), dpi=600)
save color table image