There is disclosed a process and apparatus for scanning imaged storage photo-stimuable phosphor plates including automatic gain capabilities once scanning of the thus imaged plate is initiated permitting preliminary reading of a portion of the storage foil or photo-stimuable phosphor imaging plate to determine pixel values for evaluation within a predetermined range, and adjusting the gain if such pixel value is outside the predetermined range by modifying the high voltage supply setting and thence to complete generation of a computer stored image having maximum depth of field.