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

The development of multi-channel inkjet printing methodologies for fine art applications

This thesis contributes to the defence of the practitioner perspective as a means of undertaking problems addressed predominantly in the field of colour science. Whilst artists have been exploring the use of colour for centuries through their personal practice and education, the rise of industrialised printing processes has generated a shift in focus away from these creative pursuits and into the computational field of colour research. It is argued here that the disposition and knowledge generated by creative practice has significant value to offer developing technologies. While creative practice has limited influence in the development of colour printing, practitioners and users of technology actively engage with the process in ways that extend beyond its intended uses in order to overcome recognised shortcomings. Here consideration is given to this creative engagement as motivation to develop bespoke printing parameters that demonstrate the effects of colour mixing through methods alternative to standard workflows. The research is undertaken incorporating both qualitative and quantitative analysis, collecting data from visual assessments and by examining spectral measurements taken from printed output. Action research is employed to directly access and act upon the constant developments in the art and science disciplines related to inkjet printing, observing and engaging with current methods and techniques employed by practitioners and developers. This method of research has strongly informed the empirical testing that has formed this thesis’s contribution to fine art inkjet printing practice. The research follows a practitioner led approach to designing and testing alternative printing methods and is aimed at expanding the number of discernible colours an inkjet printer can reproduce. The application of this methodology is evidenced through demonstrative prints and a reproduction study undertaken at the National Gallery, London. The experimentation undertaken in partnership with the National Gallery has proven the ability to increase accuracy between colour measured from the original target and reproduction, beyond the capabilities of current inkjet printing workflows

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

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

A Designer\u27s guide to the evaluation of digital proofs

Digital color proofs and pre-proofs are used by graphic artists and commercial printers throughout the prepress process. However the prepress process has undergone radical changes over the past decade due to the introduction of desk top publishing and desktop prepress. Alongside of the desktop publishing revo lution has come a multitude of new digital proofing technologies for use in this ever changing environment. Technologies including, but not limited to, liquid inkjet, dye sublimation, continuous inkjet, color laser, and thermal wax transfer printers have provided an entire range of color accuracy and price suitability to many of their users. However one needs to be able to understand the practical applications and limitations of these technologies to make a suitable choice for a specific prepress operation or design process. Therefore a handbook for the users of digital proofs has been created for their benefit. The underlying structure of this handbook is based on the following six chap ters. The first chapter, entitled Communicating with Prepress and the Attributes of Digital Proofing, contains multiple parts. Firstly, it contains information for the designer in regards to the advantages and disadvantages of all types of digital output devices. It discusses the advantages which digital output devices may or may not have over conventional proofing systems. Additionally, ideas such as the vantages and drawbacks of preproofers and proofers is elaborated upon. Information for this part of the chapter was obtained through questionnaires completed by, and interviews with print buyers, art directors, and production managers from advertising agencies and prepress providers in the Rochester area. More information for this section of the first chapter was obtained through various manufacturer\u27s literature, printing industry reports and various periodi cals. Chapter One also discusses ideas behind the application of color printers (preproofers) and digital proofers. These ideas address issues which pertain to the application of specific printing and proofing processes to specific phases of the creative and production processes. Additionally, discussions regarding proof ing costs, qualities, and production turnaround time may be found in this part of the first chapter. Information for this section of Chapter One was obtained through information found in printing and publishing related periodicals, as well as in manufacturers\u27 literature. Finally, the first chapter develops a system for the correction of digital preproofs and proofs. Multiple groups of ideas pertaining to the correction of digital output are discussed. Some of these include sections entitled Digital File Tracking and Identification, Evaluation of Design Elements, Evaluating Colors, Element Positioning, and Element Dimension Adjustments. Information for this part of the chapter was obtained through the evaluation of previously corrected digital con tract proofs and preproofs, as well as the interviews and questionnaires men tioned above. The second chapter, entitled Proofing Typography, displays the many different ways that printing and proofing technologies affect text type and display typog raphy. Using the CD-Rom included in the back of the book, one may view on screen how the following technologies affect type ranging from 3 points to 72 points in size: liquid inkjet, large format liquid inkjet, phase-change inkjet, ther mal wax transfer, dye sublimation, continuous inkjet, and dye ablation. Information and samples for this chapter were obtained through printing and proofing system manufacturers and advertising agencies in the Rochester area. The Color Primer and Chapter Three: Proofing for Imagery and Color, contain information for the designer which may be applied to proper evaluation of color on color prints and digital proofs. The Color Primer discusses subjects such as color space, the additive and subtractive color theories, and common color mea surement tools. Chapter Three then applies some of this knowledge in its discus sions of proper lighting conditions for viewing prints and proofs, and different human factors which influence the highly subjective evaluation of all digital color output. Information for this chapter was gathered using graphic arts and printing industry related periodicals and industry-wide books related to color and its reproduction. The fourth chapter, entitled Substrates and Digital Output, educates the design er about the effects on text, imagery, and graphics which occur when creating digital prints and proofs on a variety of papers. Various paper surfaces such as gloss, semi-gloss and matte surfaces are addressed. The affects of colored paper on imagery and graphics are also elaborated upon. Additionally, printing and proofing processes are discussed in regards to the substrates that they accept for output. Information for this chapter was gathered through manufacturers\u27 litera ture and various industry related books and periodical articles. The Proofing Process Supplement was created to familiarize the designer with all currently popular forms of digital output technology. The process supplement discusses the imaging processes used by the following digital output technolo gies: liquid inkjet, phase-change inkjet, thermal wax transfer, dye sublimation, continuous inkjet, and dye ablation. Additionally, the supplement contains brief explanations regarding screening technologies. Information for the process sup plement was gathered through manufacturers\u27 literature, interviews with pre press providers in the Rochester area, and interviews with technical representa tives from the manufacturers of devices which use the above digital, color out put technologies. Chapter Five, entitled Image Fidelity, simply illustrates how all of the current ly popular printing and proofing technologies affect graphics and imagery. Using the CD-Rom included with the guidebook, the reader may view magni fied and normal views of printing and proof sample imagery. Information noted by the reader in the proofing process supplement may then be actively applied when viewing these samples. Information and sample prints for the fifth chapter were gathered from several manufacturers and advertising agencies in the Rochester area. The sixth chapter, entitled The Acceptance of Digital Contract Proofing, discusses a new definition of the contract proof in regards to the evolution of digital proof ing. This chapter provides ideas for the designer, art director, and print buyer to realize when considering the use of digital contract proofing. Several questions are raised concerning what requirements a digital contract proof must fulfill depending upon the areas of its application and any agreements between the designer and prepress provider regarding their specific definition of a digital contract proof. Additionally, specific advantages of digital contract proofs, such as their ability to fingerprint a press and/or press run, are discussed. Finally, a discussion pertaining to the education of all users of digital proofing technolo gies is presented to aid the overall acceptance of digital contract proofing. Information for this chapter was obtained through the extensive interviews of leading technical and product oriented representatives from the manufacturers of currently used digital contract proofing systems. Many conclusions have been reached with the completion of this guidebook. In brief, the first and most prominent conclusion which may be reached states that the acceptance of digital contract proofing lies within the education of all designers, art directors and print buyers about digital printing and proofing technologies. As the use of digital contract proofing grows, education and inter est by all creative professionals will orient them towards their use of digital proofing systems. The next conclusion which has been reached is that the proper application of color printers and digital proofers is of major importance for the designer due to the added flexibility and rewards which result from the use of digital color out put devices throughout the creative and production processes. Another conclu sion which may be reached is that the display of proofing and printing process effects on text, graphics, and imagery serves to directly inform the creative pro fessional how these elements may be distorted by the utilized output device. Knowledge gained by the creative professional in regards to these effects helps to answer many questions regarding print or proof quality and proper output device application. Finally, additional knowledge gained by designers which pertains to proper viewing of all color output, color theories, color measurement, and proofing sub strates helps them to better communicate with those prepress and print professionals involved in the production process

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

An Improved Approach To Watercolor Reproduction By Profile Editing

Fine art is usually produced on paper or canvas as a one-of-a-kind artwork. Fine art may be reproduced in limited editions and put up for sale as art. Different printing technologies have been used in fine art reproduction such as lithography, screenprinting, and most recently inkjet. The research aspect of watercolor reproduction has been the question of how good is good enough. In this case, the artists demand the exact match between the original watercolor and its reproduction. While there are difficulties in quantifying the degree of color image match, the initial testing of watercolor reproduction using a colormanaged approach with an inkjet printer showed that there is a need to improve the reproduction quality. The objective of this study is to see if accuracy of watercolor reproduction can be improved by using profile editing tools. The significance of the research is the potential to achieve higher reproduction quality in watercolor by means of profile editing. In addition, we can put control back in the hands of content creators for limited editions. This research begins with a literature review. The review discusses how artworks are being digitized and reproduced by museums. It points out the wide adoption of International Color Consortium (ICC) color management practices in printing and publishing. It also covers how a color image match between an original and its reproduction is assessed quantitatively and qualitatively. The quantitative analyses of Macbeth ColorChecker between a generic ICC profile and a custom ICC profile were used to test first hypothesis, i.e., if there is any significant difference in measured color accuracy of watercolor reproductions between a generic ICC profile and a custom ICC profile. The results indicate that there is a significant difference in color accuracy of watercolor reproduction between using generic ICC profile and the custom ICC profile state findings. To our surprise, the custom ICC profile performed worse than the generic ICC profile. A possible cause of the large color differences was attributed to the accuracy of the scanner profile. A paired comparison method was used to test the second hypothesis, i.e., if there is any significant visual difference in color accuracy of watercolor reproductions between an unedited ICC profile and an edited ICC profile. The results indicate that there is no significant difference in color accuracy of watercolor reproduction between an unedited ICC profile and an edited ICC profile state findings. To our surprise once again, edited profiles did not perform color matching any better than unedited profiles. A major factor is that editing of tone reproduction and gray balance are treated as two separate events in the profile editing process. In fact, tone reproduction and gray balance are dependent on each other

Color Managing for Papers Containing Optical Brightening Agents

The role of a color-managed inkjet proof is to predict and simulate the visual appearance of printed color. The proof-to-print visual match works well under different viewing conditions when the input ICC profile and the output ICC profile, built from characterization datasets, do not contain optical brightening agents (OBA). OBAs influence printed color when measured for characterization and viewed. These brightening agents absorb UV wavelengths in the illuminant and fluoresce in the blue wavelengths. As more and more OBAs are used in printing paper production, the role of color proofing becomes more difficult. The difference in the amount of the UV component of the measuring and viewing light sources cause a problem where the OBA effect, as measured, may not be the same amount of OBA effect that should be proofed under the viewing illuminant. There are two objectives in this research project. The first objective is to show how printed colors, under identical printing conditions on OBA and non-OBA substrates, look different than when they are proofed using current characterization for proofing practices. Both M0 (UV-included) and M2 (UV-cut) measurement data are collected from color patches with selected tonal values and input ICC profiles created from this data are used to proof the brightened reference print. The results show that the UV-cut characterization treatment produces a very poor proof to the reference, while the UV-included proof was ranked as a fairly high match. A third commercially available software designed to improve upon the UV-included treatment, the X-Rite Optical Brightened Compensation module, was also tested and found to be a good match to the reference as well. The second objective is to propose different ways the characterization data can be adjusted for the OBAs in a reference print on brightened paper, by accounting for the influence of UV in the measurement illuminant, and the influence of UV in the viewing illuminant. By means of psychometric analyses, the results show that (1) the proof-to- print match is the worst when OBA in print and UV in the measurement illuminant are not addressed (UV-cut characterization data from M2); (2) although not conclusive, the proof-to-print match improves when OBA in print, UV in the measurement illuminant (characterization data from M0), and UV in the viewing illuminant are addressed

An Investigation into the relationship between contrast and resolution of a printing system using the RIT contrast resolution test target

A problem arises when different printing systems are used to print images. Different systems have considerably different contrast and resolution capabilities while an individual printing system might have a low resolution capability, the system may have the ability to render low contrast detail. Similarly, if a printing system has a high resolution capability, it does not necessarily mean that such a system has the ability to render low contrast detail well. Such contrast and resolution restrictions may be attributed to the capabilities of the PostScript interpreter, the screening method used by the RIP, the image transfer method of the output device, the substrate used, or a combination of these factors. The RIT Contrast Resolution Test Target has been developed to measure the relationship between contrast and resolution of a printing system. The target measures the contrast-resolution capability of the printing system in both the horizontal and vertical print direction of the printing device. A graph can be plotted to show the Contrast Sensitivity (CS) for the printing system. From this distribution, a contrastresolution- volume (CRV) can be calculated to produce a quantitative contrast-resolution measurement for an individual printing system. The hypothesis of this thesis is that the RIT Contrast Resolution Test Target can provide a method of discriminating the CRV of marking engines and screening methods by using analysis methods intended for use with the target. The target was printed on several printing systems. 12 observers were used to measure the target. The observers were given instruction on proper target reading, and their observations were recorded as CRV measurements. The CRV values for all colors from each system were averaged for each observer. The averaged data was entered into a two-way ANOVA test, where the two dimensions in the test were systems and observers. The results of the ANOVA test showed that there was significant variance in the average CRV values from each system, and the hypothesis of this thesis was accepted. In addition, the ANOVA test indicated that there was significant variance between the observers readings. Although each observer used a different judging criteria, it was concluded that the observers evaluated the different systems relative to one and other in almost the same sequence