A system and method are used to form features on a substrate. The method includes the steps of reading reference information from a memory, measuring the amount of light reflected from a medium on which a target image is printed by applying light to the medium, and calculating the optical density of the target image using the reference information and the measured amount of light reflected from the medium. The power generator is configured to generate power based on an interaction with at least one aspect of the device it is coupled thereto. A shift circuit is provided for the redundant row group and the shift circuit for the redundant row group receives the row select signal for only the adjacent row group. The difference in phase between the measurement and reference areas with the second body not present is subtracted from the difference in phase between the measurement and reference areas with the second body present.