Signals obtained from a sensor array that includes a plurality of energy transducers are processed. A converter used in this processing generates a plurality of converted signals by applying processing to signals from the energy transducers on a block by block basis, wherein the block is a sensor block comprising a prescribed number of neighboring energy transducers. The plurality of converted signals generated by the converter include a first converted signal, which includes a local mean and is generated by adding signals obtained from the sensor block, and a second converted signal, which includes difference between signals obtained from the sensor block. The converted signals produced by the converter are output simultaneously or sequentially.