An instrument and method for scanning all or part of a large specimen mounted on a specimen holder takes a plurality of measurements of each pixel in the whole or part of the specimen being scanned at a plurality of exposure values. A computer controls the movement of the specimen holder during scanning and again of the detector to produce a digitized image of all or part of the specimen with larger dynamic range than the dynamic range of the detection system. In a further embodiment, the instrument can scan two successive, identical strips at a different exposure values and combine the images from the two scans into one digitized image having a larger dynamic range than the dynamic range of the detection system.