The present invention uses a pattern that enables image quality maintaining control to be performed at a resolution lower than that used for a normal image forming process. The network includes at least one light-trail associated with one of the wavelengths and established between a subset of the nodes in the network. The first porous subsections are formed so as to be photoluminescent and the second subsections are formed so as to be non-photoluminescent. The first characteristic value is characteristic of the deviation between the outlet temperature of a final super heater heating surface of the respective pressure stage on the flow medium side and a predetermined nominal temperature value.