Characterisation of the n-colour printing process using the spot colour overprint model.

Kiran Deshpande,Phil Green,Michael R Pointer

doi:10.1364/oe.22.031786

Abstract

This paper is aimed at reproducing the solid spot colours using the n-colour separation. A simplified numerical method, called as the spot colour overprint (SCOP) model, was used for characterising the n-colour printing process. This model was originally developed for estimating the spot colour overprints. It was extended to be used as a generic forward characterisation model for the n-colour printing process. The inverse printer model based on the look-up table was implemented to obtain the colour separation for n-colour printing process. Finally the real-world spot colours were reproduced using 7-colour separation on lithographic offset printing process. The colours printed with 7 inks were compared against the original spot colours to evaluate the accuracy. The results show good accuracy with the mean CIEDE2000 value between the target colours and the printed colours of 2.06. The proposed method can be used successfully to reproduce the spot colours, which can potentially save significant time and cost in the printing and packaging industry.

Highlights

Colour separation is the process by which an original colour image is decomposed into individual single-colour components for printing using primary inks, for example, cyan, magenta, yellow and black (CMYK)
This avoids hundreds of special inks, saving storage in the pressroom. It allows the combination of several print jobs into one job. This project is mainly focussed on the benefit of replacing the solid spot colours and special inks by using the n-colour printing process
In spite of the spectral printer models available for printer characterisation, they may not be used in the existing workflows owing to their complexities and computational cost

Summary

Introduction

Colour separation is the process by which an original colour image is decomposed into individual single-colour components for printing using primary inks, for example, cyan, magenta, yellow and black (CMYK). The n-colour printing process uses more than four process inks usually with the intermediate hues like orange, green, violet etc. This increases the colour gamut of a traditional four-colour printing process, but makes it more difficult to obtain the colour separation. The spot colours can be broken down into tints of process channels This avoids hundreds of special inks, saving storage in the pressroom. It allows the combination of several print jobs into one job. This project is mainly focussed on the benefit of replacing the solid spot colours and special inks by using the n-colour printing process

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Conclusion