Differences between volumes can be assessed by subtracting one volume from the other; the result is a difference map. Such differences provide one way to identify or isolate small masses in 3D reconstructions. The statistics of the volumes may be used to determine the significance of 3-dimensional features (see pages 252-254 in Three-Dimensional Electron Microscopy of Macromolecular Assemblies by J. Frank).
Before subtracting volumes, make sure they are properly aligned.
Source: docs/techs/diffmaps/diffmaps.html Page updated: 09/15/06