1. A signal processing method comprising: inputting plural image data and dividing at least one of the plural image data into plural small areas via a processor controlled system; comparing a plurality of the small areas with other image data and identifying similarity parameters based on the comparison via a processor controlled system; and generating a conversion parameter that is applied to the small areas prior to determination of the similarity parameters; making a similarity determination for at least portions of the plural image data based on the similarity parameters; and wherein individual similarity values indicating the similarity of each divided small area with the other image data are totaled, the totaled value indicating a degree of similarity based on the similarity parameters.