Energy subtraction processing method and apparatus

An energy subtraction processing apparatus, comprising:

• i) a storage means for storing frequency signals, each of which is of one of a plurality of different frequency bands and which have been obtained by transforming each of a plurality of image signals into a multi-resolution space, each of the plurality of the image signals representing one of a plurality of radiation images of a single object and being made up of a series of image signal components, the plurality of the radiation images of the single object having been formed respectively with a plurality of kinds of radiation having different energy distributions, different images of at least part of the object being embedded in the plurality of the radiation images,
• ii) a subtraction processing means for weighting the signal components of the frequency signals, which are of an identical frequency band and correspond to different image signals among the plurality of the image signals, with weight factors, which are set in accordance with the frequency band, said signal components of said frequency signals representing corresponding picture elements in frequency images represented by said frequency signals,
• said subtraction processing means subtracting the weighted signal components of said frequency signals from one another, which signal components represent corresponding picture elements in said frequency images represented by said frequency signals, a difference signal being thereby obtained for said identical frequency band,
• said subtraction processing means carrying out said weighting and subtracting operations for each of the plurality of the different frequency bands, a plurality of difference signals being thereby obtained, and
• iii) an inverse transform means for carrying out an inverse transform on said difference signals having been obtained for the plurality of the different frequency bands, an energy subtraction signal being thereby obtained.