In many applications a very accurate color needs to be achieved in print. In industrial printing this applies often to product colors which have to be consistent across printing sessions of the same product and across printing technologies (e.g. packages, labels, banners, and adds of the same product). In Enterprise printing this can apply to company logos. Currently few solutions are possible: One solution is using special inks. However, the design of the ink is not always feasible, and may be very expensive. The most common is the use of special color conversion tables. However, in most cases the accuracy of these tables is not perfect over the whole color gamut and further tweaking must be performed in order to achieve better accuracy, which increases the setup time for each job.We propose a method for spot color printing using the set of available inks on the press. Our method is an iterative scheme that contains a feedback from a simple In-Line Densitometer (ILD) located in the paper path of many industrial presses after the printing engine (all our experiments have been conducted on HP Indigo presses). Required colors are specified by their Lab values. In each iteration a new coverage is printed and measured by the ILD, the algorithm calculates the change in coverage that is estimated to provide an output that is likely closest to the target Lab values required by the user. Initial results show the achieved mean accuracy for in-gamut colors is less than 1 ΔE. This accuracy is achieved for various paper types without any need to pre-define the paper type or other parameters.
Michal Aharon, Eyal Shelef, Doron Shaked, Shlomo Harush, Tsafrir Yedid-Am, Gregory Braverman, Pavel Blinchuk, "Automatic Spot Color Matching Using In-line Densitometric Measurements" in Proc. IS&T 18th Color and Imaging Conf., 2010, pp 291 - 294, https://doi.org/10.2352/CIC.2010.18.1.art00051