Color transformation modeling for printed images using interpolation based on barycentric coordinates

This document is a report on the research of a potentially superior method of color image transformation for producing rapid and accurate printed color output from a digitized color image. The primary objective is to reduce the complexities, inaccuracies, objectionable artifacts, and processing time common to current methods of color modeling. A new method of vector-corrected mathematical modeling combined with improved color space interpolation is studied. This achievement allows for rapid automatic closed-loop color-match calibration between image capture and output devices. Currently, digital image creation or manipulation systems rely on image proof printing which is slow and often of poor color fidelity or proprietary. The ideal system would provide optimum color reproduction fidelity and rapid proof printing at a low cost. Existing systems often rely on mathematical models for image con version for printing. These models are usually a bottleneck in the proofing process and are not accurate enough for many applica tions. Increasing their accuracy rapidly increases processing time to the point of impracticality well before graphic arts quality levels are achieved. A common solution to this problem in larger systems is a massive and tediously generated color look-up table based on actual measured print samples. This method is costly and does not readily accommodate printing process changes such as paper grade or ink color. Attempts to reduce the size of these look-up tables and the large quantity of required sample measurements have been disappointing. In this thesis, new methods will be reported which should allow practical small-system color proof printing with excellent color fidelity and rapid processing. By eliminating common problems associated with color space interpolation, these new methods make closed-loop control practical with a relatively small quantity of sample measurements which can be automatically printed, scanned, and incorporated into conversion processes

Influence of ink sequence on color\u27s hue and saturation in four color halftone screen printing

The screen printing process has been the least understood and studied versus other imaging methods in the graphic arts industry. As equipment configurations improve and a continuous technological development and need for high quality output persists, this fascinating process becomes increasingly popular in several end-use applications. Such as in packaging, labeling, durable graphic films printing and even short run large format halftone graphics. There is a serious need for further deep scientific analysis of the process and its variables. One of the poorly investigated sides of the four color screen printing is the effect that ink placement has to the final color appearance of a halftone print. Several known factors can influence the color result of a screen printed image. Limitations inherent to screen printing allow for a smaller color gamut reproduction compared to other methods, but colors are reproduced vividly due to a uniform and high ink film thickness. The screen - equivalent to a printing plate - consists of a stretched porous fabric mounted on a carrier frame that is coated with a light sensitive emulsion (stencil) and subsequently exposed and hardened at the non image areas. The ink will flow through the screen mesh openings when pressure and hydraulic forces are applied by a squeegee blade system. The ink system can be cured or dried by various methods depending on its chemistry and composition. For the specific system investigated, UV curing units expose the wet ink film to high energy radiation for full polymerization. The different types of equipment configurations in screen printing are designed for various processing speeds, base material formats, ink systems of specific drying and curing characteristics and also for various end use applications. This study utilized a Kammann web screen printer with five color stations and UV curing capability for roll to roll one-pass multi color printing. This type of screen printing press is used for applications such as promotional labelling with high precision type and halftone reproduction. A popular film substrate is the polyolefin construction that delivers printability, water resistance, color strength and good process characteristics through roll to roll printing presses. The polyolefin material used for this study was supplied by Fasson Films and is constructed to give a consistent ink film deposit under the set parameters without any penetration, absorption or permeation of the ink system. The samples printed from the total graphics system were produced under the same conditions using in a period of a full working day the press, screens, ink systems and substrate, but only varying the order of the printed process colors yellow (Y), cyan (C) or process blue, magenta (M) or process red and black (K). The importance of ink sequence is determined by creating these prints under the same arrangement and evaluating the color result as it relates to the sequence followed. The purpose of this study was to determine the effect of the ink sequence to the final color appearance of fully dried /cured ink film as expressed by its hue and saturation characteristics. The ink sequence is treated as the sole variable and all other parameters remain constant. An image was designed specifically for this process containing solids, tints and an actual halftone icon. Data was collected by a densitometer and a spectrophotometer from the individual color patches. The representative sampling consists of selected prints throughout each ink sequence run and the measured mean values of all color patches are recorded, plotted, graphed and statistically analyzed. The Hexagon GATF diagram was used to show changes from run to run, densitometric data was also graphed for comparison critique and the CIE*L*a*b* color coordinates allowed mapping of the prints for comparison analysis and color difference [delta]E* study. The data is statistically analyzed and validated versus the null hypothesis using a single factor analysis of variance (ANOVA) and Scheffe comparisons. The final visual evaluation under standard lighting conditions per ASTM standards helps to support the results and conclusion. Experience from the field supports that the ink sequence affects the final color result assuming that all other system components remain equal. This study shows that the sequences\u27 compared color is different and the ink sequence is a critical factor that should be analyzed further for the screen printing industry in order to help maintain color consistency and control. The hypotheses are supported by the study\u27s results. The ink sequence influences the color\u27s hue and saturation in four color halftone screen printing having distinct differences for every sequence that was produced during the printing run. The UV ink systems used, adhere and transfer better to the substrate instead of the ink layers. The placement of black is important for color control and trapping. If black is printed first down then the other inks trap well and a clean image is produced; if black is last, trapping is poor and consequently the color and image appearance. The target guide Nucleus Pattern Sequence Originator was ideal for color measurements and evaluation in screen printing; it is recommended for similar future research work. Densitometry and use of Hexagon diagrams is not very effective in screen printing. The use of colorimetry can show any color changes more accurately. It was also shown that the midtones are influenced the most form the change in ink sequence; especially important for trapping. Finally, two ( 2) of the ink sequences showed good results as concluded by the final evaluation. The MCYK delivered the best output in data and KMCY printed closest to the original proof

Using the contrast ratio method and achromatic transmission densitometry as a substitute for Status A transmission densitometry with the Photographic Activity Test For Enclosure Materials

The discontinuation of conventional photographic spot-reading transmission densitometers -including the widely adopted X-Rite model 310- due to the rapid decrease in demand for analogic photographic laboratory work has had a broadly felt effect in the conservation community. In the cultural heritage conservation field, instruments like the X-Rite 310 are widely used, specifically in the performance of the Photographic Activity Test (PAT) for the preservation of photographic materials. In the present research, five possible alternate metrics were investigated as substitutes for the increasingly unavailable spot reading transmission densitometers in Status-A readings as mandated by the current PAT. The analyzed metrics were: (1) ratio in reflection using normal illumination geometry and circumferential 45° viewing (0/45:c), (2) contrast ratio in reflection using diffuse illumination and 8° viewing geometry with specular component included (d/8:i), (3) contrast ratio in reflection using diffuse illumination and 8° viewing geometry with specular component excluded (d/8:e), (4) Ortho-transmission densitometry and (5) UV- transmission densitometry. The contrast ratio metric can be obtained with commonly available reflection spectrophotometers, such as the X-Rite 939 and the X-Rite SP64. The use of contrast ratio metric could open up new possibilities for measurement in the field of art reproduction and cultural heritage preservation to analyze changes in density and opacity. The proposed work analyzed the readings obtained by three measurement instruments: (1) X-Rite 361T, (2) X-Rite 939 and (3) X-Rite SP64, in a set of three achromatic transmission step-wedges (15-Step Transmission Stouffer© Graphic Arts T1530CC step-wedge) used as a surrogate for the colloidal silver strip used in the PAT. The goal was to evaluate the performance of the five proposed metrics and geometries as a possible alternative to transmission densitometry measurements when recording data using the Photographic Activity Test. The results indicate that there exists a near-perfect linear relationship between the readings using the X-Rite 361T in Ortho-transmission densitometry channel and the readings from the Status-A transmission density using the X-Rite 310 across the entire densitometric range represented by the Stouffer wedge. The UV channel measurements also exhibit a near seamless linear regression model with the Status-A readings. Both relationships were found to be statistically significant. On the other hand, the measurements with the setups using contrast ratio measurements did not exhibit the same linear relationship when the entire measurement range is considered. However, in readings of less than .95 opacity, the contrast ratio measurements did exhibit a meaningful linear relationship when compared to the Status-A transmission readings with a density value of less than 1.8, albeit still with lower correlation than both readings with the X-Rite 361T

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

The LLAB model for quantifying colour appearance

A reliable colour appearance model is desired by industry to achieve high colour fidelity between images produced using a range of different imaging devices. The aim of this study was to derive a reliable colour appearance model capable of predicting the change of perceived attributes of colour appearance under a wide range of media/viewing conditions. The research was divided into three parts: characterising imaging devices, conducting a psychophysical experiment, and developing a colour appearance model. Various imaging devices were characterised including a graphic art scanner, a Cromalin proofing system, an IRIS ink jet printer, and a Barco Calibrator. For the former three devices, each colour is described by four primaries: cyan (C), magenta (M), yellow (Y), and black (K). Three set of characterisation samples (120 and 31 black printer, and cube data sets) were produced and measured for deriving and testing the printing characterisation models. Four black printer algorithms (BPA), were derived. Each included both forward and reverse processes. A 2nd BPA printing model taking into account additivity failure, grey component replacement (GCR) algorithm gave the most accurate prediction to the characterisation data set than the other BPA models. The PLCC (Piecewise Linear interpolation assuming Constant Chromaticity coordinates) monitor model was also implemented to characterise the Barco monitor. The psychophysical experiment was conducted to compare Cromalin hardcopy images viewed in a viewing cabinet and softcopy images presented on a monitor under a wide range of illuminants (white points) including: D93, D65, D50 and A. Two scaling methods: category judgement and paired comparison, were employed by viewing a pair of images. Three classes of colour models were evaluated: uniform colour spaces, colour appearance models and chromatic adaptation transforms. Six images were selected and processed via each colour model. The results indicated that the BFD chromatic transform gave the most accurate predictions of the visual results. Finally, a colour appearance model, LLAB, was developed. It is a combination of the BFD chromatic transform and a modified version of CIELAB uniform colour space to fit the LUTCRI Colour Appearance Data previously accumulated. The form of the LLAB model is much simpler and its performance is more precise to fit experimental data than those of the other models

Colorimetric tolerances of various digital image displays

Visual experiments on four displays (two LCD, one CRT and hardcopy) were conducted to determine colorimetric tolerances of images systematically altered via three different transfer curves. The curves used were: Sigmoidal compression in L*, linear reduction in C*, and additive rotations in hab. More than 30 observers judged the detectability of these alterations on three pictorial images for each display. Standard probit analysis was then used to determine the detection thresholds for the alterations. It was found that the detection thresholds on LCD\u27s were similar or lower than for the CRT\u27s in this type of experiment. Summarizing pixel-by-pixel image differences using the 90th percentile color difference in E*ab was shown to be more consistent than similar measures in E94 and a prototype E2000. It was also shown that using the 90th percentile difference was more consistent than the average pixel wise difference. Furthermore, SCIELAB pre-filtering was shown to have little to no effect on the results of this experiment since only global color-changes were applied and no spatial alterations were used

Aiding the conservation of two wooden Buddhist sculptures with 3D imaging and spectroscopic techniques

The conservation of Buddhist sculptures that were transferred to Europe at some point during their lifetime raises numerous questions: while these objects historically served a religious, devotional purpose, many of them currently belong to museums or private collections, where they are detached from their original context and often adapted to western taste. A scientific study was carried out to address questions from Museo d'Arte Orientale of Turin curators in terms of whether these artifacts might be forgeries or replicas, and how they may have transformed over time. Several analytical techniques were used for materials identification and to study the production technique, ultimately aiming to discriminate the original materials from those added within later interventions

Proceedings of the 10th International Chemical and Biological Engineering Conference - CHEMPOR 2008

This volume contains full papers presented at the 10th International Chemical and Biological Engineering Conference - CHEMPOR 2008, held in Braga, Portugal, between September 4th and 6th, 2008.FC