Hyperspectral imaging system

A printer, comprising:

• I.) a first light source;
• II.) an image bearing surface positioned to receive light from the first light source and to form output light from the light incident thereon, the image bearing surface disposed on a drum or a belt to move the image bearing surface in a process direction;
• III.) a hyperspectral imaging system comprising:
• an input polarizer disposed within a device housing including an aperture arranged to receive and polarize the output light received via the aperture;
• a liquid crystal variable retarder disposed within the device housing and arranged after the input polarizer along a path of the output light to change polarization of the output light in a wavelength-dependent manner;
• an output polarizer disposed within the device housing and arranged to receive the wavelength-dependent polarized output light and to convert polarization state information of the output light into a form detectable as light intensity;
• a voltage source electrically connected to the liquid crystal variable retarder;
• a controller connected to the voltage source, the controller configured to control voltages applied to the liquid crystal variable retarder to control a retardance of the output light;
• a linear image sensor disposed within the device housing and having a length extending in a direction to obtain images of the output light in a cross-process direction, the linear image sensor synchronized with the controller to collect the images as a function of retardance of the liquid crystal variable retarder after the output light passes through the output polarizer, for generation of an output signal corresponding to a portion of the linear image sensor;
• an internal light source disposed within the device housing, which internal light source is separate and distinct from the first light source, arranged to output internal light emitted from within the housing to directly illuminate the input polarizer and the linear image sensor such that internal light emitted by the internal light source from within the housing is received by the linear image sensor;
• and
• IV.) a processor to perform transformations of the output signal into spectral information.