The color reproducibility of materials printed on a printer may vary due to changes in the installation environment or aging degradation of printer components. Although having provided a unicolor calibration feature to address this issue, Fuji Xerox has developed a unique 3D-calibration technology that enables calibration with higher accuracy. This technology enables the quantity of toner for a single color (single-primary color) and that for a multi-primary color (mixture of two or three primary colors) to be independently calibrated, thus making it possible to calibrate a full gamut of reproducible colors. This feature of our 3D-calibration technology enables the calibration of multi-primary colors (e.g. gray balance, skin color) that are difficult to reproduce with unicolor calibration technology.
A printer reproduces a color by overlaying the toner of C, M, Y, and K. A reproduced color varies depending on the quantity of each toner that is overlaid. However, as shown in Fig. 1, a color may not be correctly reproduced due to a change in the quantity of toner after transfer. Such a case occurs because the quantity of toner to be transferred is changed by a change in properties that affect the quantity of toner transferred onto paper.
In the conventional unicolor calibration method, the density of the reproduced color is compared with that of the target color (to be reproduced) in order to monitor the current reproducibility of a unicolor (single-primary color). Then, the quantity of toner is adjusted to make the current color consistent with the target color. Even if the same quantity of toner as that for the target color is applied, the density of the color after transfer may be different from that of the target color because the quantity of toner changes when toner is transferred onto paper. In such case, the quantity of toner is adjusted to make the density of the color on paper consistent with that of the target color.
With this method, however, the quantity of toner for a single color that constitutes a mixture of two primary colors is concurrently changed when the quantity of toner for the single color is adjusted. Therefore, even if calibration of a mixture of two primary colors is not needed, the color is also calibrated when the quantity of toner for a single color is adjusted (Fig. 2).
Our newly developed technology called 3D calibration solves this issue by comparing a reproduced multi-primary color to the target color with these colors mapped on a 3D table and generating the calibration parameters for adjusting the multi-primary color to the target color. Because each multi-primary color can be independently calibrated, a single-primary color and a mixture of two primary colors can also be adjusted to each target color without affecting the reproducibility of multi-primary colors (Fig. 2).
In order to enable high accuracy color calibration with little data, a patch chart used for 3D calibration has been optimized through a quality engineering-based analysis of the relation between the patch chart and calibration accuracy. The optimization of the color patch contributes to a significant reduction of patches without impairing calibration accuracy, thereby making color measurement with the patch chart more efficient.
In addition, the calibration feedback feature enables stable color reproducibility by improving the accuracy of a color prediction model and calibration accuracy through repetitive color calibration (Fig. 3).