Channel-separable halftone independent methods for color drift correction

Color printer calibration is the process of deriving correction functions for device signals (e.g., CMYK), so that the device can be maintained with a fixed known characteristic color response. Since the colorimetric response of the printer can be a strong function of the halftone, the calibration process must be repeated for every halftone supported by the printer. The effort involved in the calibration process thus increases linearly with the number of halftoning methods. In the past few years, it has become common for high-end digital color printers to be equipped with a large number of halftones, thus making the calibration process onerous. We propose a halftone independent method for correcting color (CMY or CMYK) printer drift. Our corrections are derived by measuring a small number of halftone independent fundamental binary patterns based on the 2×2binary printer model by Wang et al. Hence, the required measurements do not increase as more halftoning methods are added. First, we derive a halftone correction factor (HCF) that exploits the knowledge of the relationship between the true printer response and the 2×2-model predicted response for a given halftoning scheme. Therefore, the true color drift can be accurately predicted from halftone-independent measurements and corrected correspondingly. Further, we develop extensions of our proposed color correction framework to the case when the measurements of our fundamental binary patches are acquired by a common desktop scanner. Finally, we exploit the application of the HCF to correct color drift across different media (papers) and for halftoneindependent spatial nonuniformity correction.