Estimating printer misregistration from color shifts: A new paradigm

Inherent to most multi-color printing systems is the inability to achieve perfect registration between the primary separations. Because of this, dot-on-dot or dot-off-dot halftone screen sets are generally not used, due to the significant color shift observed in the presence of even the slightest misregistration. Much previous work has focused on characterizing these effects, and it is well known that dot-off-dot printed patterns result in a higher chroma (C*) relative to dot-on-dot. Rotated dot sets are used instead for these systems, as they exhibit a much greater robustness against misregistration. In this paper, we make the crucial observation that while previous work has used color shifts caused by misregistration to design robust screens, we can infact exploit these color shifts to obtain estimates of misregistration. In particular, we go on to demonstrate that even low resolution macroscopic color measurements of a carefully designed test patch can yield misregistration estimates that are accurate up-to the sub-pixel level. The contributions of our work are as follows: 1.) a simple methodology to construct test patches that may be measured to obtain misregistration estimates, 2.) derivation of a reflectance printer model for the test patch so that color deviations in the spectral or reflectance space can be mapped to misregistration estimates, and 3.) a practical method to estimate misregistration via scanner RGB measurements. Experimental results show that our method achieves accuracy comparable to the state-of-the art but expensive geometric methods that are currently used by high-end color printing devices to estimate misregistration.