A model for colour prediction of halftoned samples incorporating light scattering and ink spreading

A model for color prediction of halftoned samples incorporating light scattering and ink spreading was presented. The spreading process was modeled by enlarging the drop impact according to the configuration of its neighbors and the state of the surface. The spectra of halftoned samples produced with one ink were predicted with an average prediction error or about δE=1.4 in CIELAB. For two halftoned ink layers, good spectral predictions were achieved with an average error of about δE=2.1 in CIELAB

A Model for Colour Prediction of Halftoned Samples Incorporating Light Scattering and Ink Spreading

This study introduces new models and mathematical formulations describing the light scattering and ink spreading phenomena. Based on these new theoretical tools, the spectra of 100 real paper samples produced by two ink-jet printers were computed with an average prediction error of about in CIELAB. Keywords: spectral colour prediction, light scattering, ink spreading, halftones, ink-jet printing. Introduction Several physical phenomena influence colours reproduced by ink-jet printers. This makes accurate colour prediction very difficult. The dot gain effect is generally considered to have the largest impact on colour deviations. Dot gain is caused by light scattering or by ink spreading or both together. Intensive investigations on optical dot gain (YuleNielsen effect) have been made, 2,10,25 but the resulting prediction models are often very complex. We propose a global approach incorporating all physical contributing phenomena into a single model using a mathematical framework b..

N-colour separation methods for accurate reproduction of spot colours

In packaging, spot colours are used to print key information like brand logos and elements for which the colour accuracy is critical. The present study investigates methods to aid the accurate reproduction of these spot colours with the n-colour printing process. Typical n-colour printing systems consist of supplementary inks in addition to the usual CMYK inks. Adding these inks to the traditional CMYK set increases the attainable colour gamut, but the added complexity creates several challenges in generating suitable colour separations for rendering colour images. In this project, the n-colour separation is achieved by the use of additional sectors for intermediate inks. Each sector contains four inks with the achromatic ink (black) common to all sectors. This allows the extension of the principles of the CMYK printing process to these additional sectors. The methods developed in this study can be generalised to any number of inks. The project explores various aspects of the n-colour printing process including the forward characterisation methods, gamut prediction of the n-colour process and the inverse characterisation to calculate the n-colour separation for target spot colours. The scope of the study covers different printing technologies including lithographic offset, flexographic, thermal sublimation and inkjet printing. A new method is proposed to characterise the printing devices. This method, the spot colour overprint (SCOP) model, was evaluated for the n-colour printing process with different printing technologies. In addition, a set of real-world spot colours were converted to n-colour separations and printed with the 7-colour printing process to evaluate against the original spot colours. The results show that the proposed methods can be effectively used to replace the spot coloured inks with the n-colour printing process. This can save significant material, time and costs in the packaging industry