A method of imaging a specimen in a Scanning Transmission Charged Particle Microscope, comprising the following steps: Providing the specimen on a specimen holder; Providing a beam of charged particles that is directed from a source through an illuminator so as to irradiate the specimen; Providing a segmented detector for detecting a flux of charged particles traversing the specimen; Causing said beam to scan across a surface of the specimen, and combining signals from different segments of the detector so as to produce a vector output from the detector at each scan position, said vector output having components Dx, Dy along respective X, Y coordinate axes, specifically comprising: Performing a relatively coarse pre-scan of the specimen, along a pre-scan trajectory; At selected positions pi on said pre-scan trajectory, analyzing said components Dx, Dy and also a scalar intensity sensor value Ds; Using said analysis of Dx, Dy and Ds to classify a specimen composition at each position pi into one of a group of composition classes; For a selected composition class, performing a relatively fine scan at positions pi assigned to that class.