iface.mapCanvas().setExtent(QgsRectangle(xmin, ymin, xmax, ymax))
time.sleep(5)
iface.mapCanvas().refresh()
time.sleep(5)
iface.mapCanvas().saveAsImage("D:/GE"+str(i)+"to"+str(j)+"img.png" )

for layer in qgis.utils.iface.mapCanvas().layers():
    layer.triggerRepaint()