Spectral modeling of a six-color inkjet printer

After customizing an Epson Stylus Photo 1200 by adding a continuous-feed ink system and a cyan, magenta, yellow, black, orange and green ink set, a series of research tasks were carried out to build a full spectral model of the printers output. First, various forward printer models were tested using the fifteen two color combinations of the printer. Yule- Nielsen-spectral-Neugebauer (YNSN) was selected as the forward model and its accuracy tested throughout the colorant space. It was found to be highly accurate, performing as well as a more complex local, cellular version. Next, the performance of nonlinear optimization-routine algorithms were evaluated for their ability to efficiently invert the YNSN model. A quasi-Newton based algorithm designed by Davidon, Fletcher and Powell (DFP) was found to give the best performance when combined with starting values produced from the non-negative least squares fit of single-constant Kubelka- Munk. The accuracy of the inverse model was tested and different optimization objective functions were evaluated. A multistage objective function based on minimizing spectral RMS error and then colorimetric error was found to give highly accurate matches with low metameric potential. Finally, the relationship between the number of printing inks and the ability to eliminate metamerism was explored

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

Lightfastness of Water-based Inks vs. Latex Water-based Inks

This study focused on the lightfastness properties of non-latex water-based inkjet inks and latex inkjet inks for conventional process colors, i.e., cyan, magenta, yellow, and black. Lightfastness is defined as the property of ink that describes the degree of resistance to fading when exposed to light. Lightfastness varies among inks based on their formulation. The degradation of inks caused by light happens when the light is absorbed by the pigments and reacts with the pigments and molecules in the printed substrate. This research evaluated the lightfastness degree of water-based inkjet inks vs. latex inkjet inks. The experiment used printed samples subjected to equal amounts of light, using established methodologies for accelerated aging. The data gathered from the prints included information on color shift as expressed by L*a*b* and ∆E00. Data analysis was performed to compare the before and after exposures of the two types of ink. It was concluded that the latex inkjet ink formulation improved the lightfastness properties when compared to water-based inkjet inks, particularly with magenta and cyan

A New Anti-Counterfeiting Feature Relying on Invisible Luminescent Full Color Images Printed with Lanthanide-Based Inks

Europium and terbium trisdipicolinate complexes are inkjet printed onto paper with commercially available desktop inkjet printers. Together with a commercial blue luminescent ink, the red-emitting luminescent ink containing europium and the green-emitting luminescent ink containing terbium are used to reproduce accurate full color images that are invisible under white light and appear under a 254 nm UV light. Such invisible luminescent images are attractive anti-counterfeiting security features. The luminescent prints have a color range (gamut) nearly as wide as the gamut of a standard sRGB display. The gamut of the luminescent prints is determined by relying on a simple model predicting the relative spectral radiant emittances of any printed luminescent color halftone. The model is also used to establish the correspondence between the surface coverages of the printed luminescent inks and the emitted color of these luminescent halftones. The accuracy of the spectral prediction model is very good and can be rationalized by the absence of quenching when the luminescent lanthanide complexes are printed in superposition with the other luminescent materials

Digital Color Imaging

This paper surveys current technology and research in the area of digital color imaging. In order to establish the background and lay down terminology, fundamental concepts of color perception and measurement are first presented us-ing vector-space notation and terminology. Present-day color recording and reproduction systems are reviewed along with the common mathematical models used for representing these devices. Algorithms for processing color images for display and communication are surveyed, and a forecast of research trends is attempted. An extensive bibliography is provided

Test Targets 7.0: A Collaborative effort exploring the use of scientific methods for color imaging and process control

Test Targets is a culmination of teaching and learning that reflects quality and analytic aspects of printing systems and their optimization. The creation of the Test Targets publication is a total experience that reflects the innovation, problem solving, and teamwork of the diverse team of faculty, staff, students, and professionals responsible for its contents and production

Test Targets 8.0: A Collaborative effort exploring the use of scientific methods for color imaging and process control

Publishing is both a journey and a destination. In the case of Test Targets, the act of creating and editing content, paginating and managing digital assets, represents the journey. The hard copy is the result or destination that readers can see and touch. Like the space exploration program, everyone saw the spacecraft that landed on the moon. It was the rocket booster that made the journey from the earth to the moon possible. This article portrays the process of capturing ideas in the form of digital data. It also describes the process of managing digital assets that produces the Test Targets publication

Developing a spectral and colorimetric database of artist paint materials

As the project of the author\u27s Master\u27s thesis, the development of a spectral and colorimetric database of artist paint materials for acrylic paints was started. The goal of this research project was to: - provide the academic resource of colorant spectral characteristics - give scientifc explanations on various paint-particular phenomena (paint mixing, gloss effects and color gamut expansion by varnishing) These tasks were planned to satisfy possible interests on paint research from not only conservators in museums but also color educators in schools and color reproduction engineers in imaging companies