Combined dust protection and dark calibration slide for a flat-bed scanner

A scanner for scanning an original document to obtain a digitized representation of said original document, said scanner comprising:

• a stationary reflective object focal plane for supporting a reflective original document;
• a stationary transmissive object focal plane, disposed substantially parallel to and at a vertical distance below said stationary reflective object focal plane, for supporting a transmissive original document;
• means for selecting between said stationary reflective object focal plane and said stationary transmissive object focal plane;
• a scan carriage movably disposed for linear motion along a scanning axis, said scan carriage including an illumination source disposed between said stationary reflective object focal plane and said stationary transmissive object focal plane for illuminating a scan line of said original document located in said selected object focal plane, said scan carriage further including an enclosure disposed below said stationary transmissive object focal plane including optical imaging and sensor means for obtaining a digitized representation of said scan line;
• means for moving said scan carriage along said scanning axis to obtain digitized representations of successive scan lines of said original document in said selected object focal plane, said digitized representations of said successive scan lines together comprising said digital representation of said original document;
• and means for selectively sealing said enclosure.