Two approaches in scanner-printer calibration: colorimetric space-based versus closed-loop

The present paper studies two different table-based approaches for the calibration of electronic imaging systems. The first approach, which is the classical one,uses the device-independent CIE-XYZ colorimetric space as an intermediate standard space. Input and output devices such as scanners, displays and printers are calibrated separately with respect to the objective CIE-XYZ space. The calibration process requires establishing a 3-dimensional mapping between a scanner’s device-dependent RGB space and a device-independent colorimetric space such as CIE-XYZ. Measured samples belonging to the calibration set are used for splitting the colorimetric space into Delaunay tetrahedrons. The second approach, the so-called closed loop approach, calibrates directly scanner-printer pairs, without any reference to an objective colorimetric space. It enables a 3-D mapping to be built between the scanner’s RGB space and the printer’s CMY space without requiring any colorimetric measurement. It offers very accurate calibrated output for input samples having the same characteristics (halftone dot, ink spectral reflectance) as the printed samples used for the calibration process. When the desktop scanners’ RGB sensibilities are not a linear transform of the CIE x, y, z matching curves, an accurate calibration can only be made if input color patches are based on the same primary inks as the patches used for device calibration.