Scanner Color Chart Making and its Application in Printing Color Conversion

Digitizing a color image with a scanner means to represent the image´s colorimetric values with its RGB response signals. For one scanner, there always exists a determinate transform relation between the two set of values under a certain scanning condition. And the transform derivation process is called as scanner characterization. In ICC color management system, color chart generally used for characterizing scanners is the ANSI IT8 chart, i.e., IT8.7/2. But the IT8 chart is not well suitable for printing color conversion application, typically due to the fact that its colors have not covered the ordinarily printing color gamut. In this study, a proof printer, which could offer colors in a bigger color space than offset printing gamut, was used to output a new color chart throughout effectively controlled. The made new color chart contains 425 colors that more evenly space in CIELAB color space. Based on the new target, a color transform relation was derived by adopting a space-divided polynomial modeling method for an experimental scanner. The resulting average and maximal transformation color-differences within all the reference colors, in CIELAB unit, were 0.98 and 5.22 respectively, lower than 1.17 and 16.98 based on the profile transform, which was obtained by using the IT8 target and profile-making software.