229 research outputs found

    Digital Color Imaging

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    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

    Pushing the Limits of 3D Color Printing: Error Diffusion with Translucent Materials

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    Accurate color reproduction is important in many applications of 3D printing, from design prototypes to 3D color copies or portraits. Although full color is available via other technologies, multi-jet printers have greater potential for graphical 3D printing, in terms of reproducing complex appearance properties. However, to date these printers cannot produce full color, and doing so poses substantial technical challenges, from the shear amount of data to the translucency of the available color materials. In this paper, we propose an error diffusion halftoning approach to achieve full color with multi-jet printers, which operates on multiple isosurfaces or layers within the object. We propose a novel traversal algorithm for voxel surfaces, which allows the transfer of existing error diffusion algorithms from 2D printing. The resulting prints faithfully reproduce colors, color gradients and fine-scale details.Comment: 15 pages, 14 figures; includes supplemental figure

    The development of the toner density sensor for closed-loop feedback laser printer calibration

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    A new infrared (IR) sensor was developed for application in closed-loop feedback printer calibration as it relates to monochrome (black toner only) laser printers. The toner density IR sensor (TDS) was introduced in the early 1980’s; however, due to cost and limitation of technologies at the time, implementation was not accomplished until within the past decade. Existing IR sensor designs do not discuss/address: • EMI (electromagnetic interference) effects on the sensor due to EP (electrophotography) components • Design considerations for environmental conditions • Sensor response time as it affects printer process speed The toner density sensor (TDS) implemented in the Lexmark E series printer reduces these problems and eliminates the use of the current traditional “open-loop” (meaning feedback are parameters not directly affecting print darkness such as page count, toner level, etc.) calibration process where print darkness is adjusted using previously calculated and stored EP process parameters. The historical process does not have the ability to capture cartridge component variation and environmental changes which affect print darkness variation. The TDS captures real time data which is used to calculate EP process parameters for the adjustment of print darkness; as a result, greatly reducing variations uncontrolled by historical printer calibration. Specifically, the first and primary purpose of this research is to reduce print darkness variation using the TDS. The second goal is to mitigate the TDS EMI implementation issue for reliable data accuracy

    Laser scanner jitter characterization, page content analysis for optimal rendering, and understanding image graininess

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    In Chapter 1, the electrophotographic (EP) process is widely used in imaging systems such as laser printers and office copiers. In the EP process, laser scanner jitter is a common artifact that mainly appears along the scan direction due to the condition of polygon facets. Prior studies have not focused on the periodic characteristic of laser scanner jitter in terms of the modeling and analysis. This chapter addresses the periodic characteristic of laser scanner jitter in the mathematical model. In the Fourier domain, we derive an analytic expression for laser scanner jitter in general, and extend the expression assuming a sinusoidal displacement. This leads to a simple closed-form expression in terms of Bessel functions of the first kind. We further examine the relationship between the continuous-space halftone image and the periodic laser scanner jitter. The simulation results show that our proposed mathematical model predicts the phenomenon of laser scanner jitter effectively, when compared to the characterization using a test pattern, which consists of a flat field with 25% dot coverage However, there is some mismatches between the analytical spectrum and spectrum of the processed scanned test target. We improve experimental results by directly estimating the displacement instead of assuming a sinusoidal displacement. This gives a better prediction of the phenomenon of laser scanner jitter. ^ In Chapter 2, we describe a segmentation-based object map correction algorithm, which can be integrated in a new imaging pipeline for laser electrophotographic (EP) printers. This new imaging pipeline incorporates the idea of object-oriented halftoning, which applies different halftone screens to different regions of the page, to improve the overall print quality. In particular, smooth areas are halftoned with a low-frequency screen to provide more stable printing; whereas detail areas are halftoned with a high-frequency screen, since this will better reproduce the object detail. In this case, the object detail also serves to mask any print defects that arise from the use of a high frequency screen. These regions are defined by the initial object map, which is translated from the page description language (PDL). However, the information of object type obtained from the PDL may be incorrect. Some smooth areas may be labeled as raster causing them to be halftoned with a high frequency screen, rather than being labeled as vector, which would result in them being rendered with a low frequency screen. To correct the misclassification, we propose an object map correction algorithm that combines information from the incorrect object map with information obtained by segmentation of the continuous-tone RGB rasterized page image. Finally, the rendered image can be halftoned by the object-oriented halftoning approach, based on the corrected object map. Preliminary experimental results indicate the benefits of our algorithm combined with the new imaging pipeline, in terms of correction of misclassification errors. ^ In Chapter 3, we describe a study to understand image graininess. With the emergence of the high-end digital printing technologies, it is of interest to analyze the nature and causes of image graininess in order to understand the factors that prevent high-end digital presses from achieving the same print quality as commercial offset presses. We want to understand how image graininess relates to the halftoning technology and marking technology. This chapter provides three different approaches to understand image graininess. First, we perform a Fourier-based analysis of regular and irregular periodic, clustered-dot halftone textures. With high-end digital printing technology, irregular screens can be considered since they can achieve a better approximation to the screen sets used for commercial offset presses. This is due to the fact that the elements of the periodicity matrix of an irregular screen are rational numbers, rather than integers, which would be the case for a regular screen. From the analytical results, we show that irregular halftone textures generate new frequency components near the spectrum origin; and these frequency components are low enough to be visible to the human viewer. However, regular halftone textures do not have these frequency components. In addition, we provide a metric to measure the nonuniformity of a given halftone texture. The metric indicates that the nonuniformity of irregular halftone textures is higher than the nonuniformity of regular halftone textures. Furthermore, a method to visualize the nonuniformity of given halftone textures is described. The analysis shows that irregular halftone textures are grainier than regular halftone textures. Second, we analyze the regular and irregular periodic, clustered-dot halftone textures by calculating three spatial statistics. First, the disparity between lattice points generated by the periodicity matrix, and centroids of dot clusters are considered. Next, the area of dot clusters in regular and irregular halftone textures is considered. Third, the compactness of dot clusters in the regular and irregular halftone textures is calculated. The disparity of between centroids of irregular dot clusters and lattices points generated by the irregular screen is larger than the disparity of between centroids of regular dot clusters and lattices points generated by the regular screen. Irregular halftone textures have higher variance in the histogram of dot-cluster area. In addition, the compactness measurement shows that irregular dot clusters are less compact than regular dot clusters. But, a clustered-dot halftone algorithm wants to produce clustered-dot as compact as possible. Lastly, we exam the current marking technology by printing the same halftone pattern on different substrates, glossy and polyester media. The experimental results show that the current marking technology provides better print quality on glossy media than on polyester media. With above three different approaches, we conclude that the current halftoning technology introduces image graininess in the spatial domain because of the non-integer elements in the periodicity matrix of the irregular screen and the finite addressability of the marking engine. In addition, the geometric characteristics of irregular dot clusters is more irregular than the geometric characteristics of regular dot clusters. Finally, the marking technology provides inconsistency of print quality between substrates

    A New framework for an electrophotographic printer model

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    Digital halftoning is a printing technology that creates the illusion of continuous tone images for printing devices such as electrophotographic printers that can only produce a limited number of tone levels. Digital halftoning works because the human visual system has limited spatial resolution which blurs the printed dots of the halftone image, creating the gray sensation of a continuous tone image. Because the printing process is imperfect it introduces distortions to the halftone image. The quality of the printed image depends, among other factors, on the complex interactions between the halftone image, the printer characteristics, the colorant, and the printing substrate. Printer models are used to assist in the development of new types of halftone algorithms that are designed to withstand the effects of printer distortions. For example, model-based halftone algorithms optimize the halftone image through an iterative process that integrates a printer model within the algorithm. The two main goals of a printer model are to provide accurate estimates of the tone and of the spatial characteristics of the printed halftone pattern. Various classes of printer models, from simple tone calibrations, to complex mechanistic models, have been reported in the literature. Existing models have one or more of the following limiting factors: they only predict tone reproduction, they depend on the halftone pattern, they require complex calibrations or complex calculations, they are printer specific, they reproduce unrealistic dot structures, and they are unable to adapt responses to new data. The two research objectives of this dissertation are (1) to introduce a new framework for printer modeling and (2) to demonstrate the feasibility of such a framework in building an electrophotographic printer model. The proposed framework introduces the concept of modeling a printer as a texture transformation machine. The basic premise is that modeling the texture differences between the output printed images and the input images encompasses all printing distortions. The feasibility of the framework was tested with a case study modeling a monotone electrophotographic printer. The printer model was implemented as a bank of feed-forward neural networks, each one specialized in modeling a group of textural features of the printed halftone pattern. The textural features were obtained using a parametric representation of texture developed from a multiresolution decomposition proposed by other researchers. The textural properties of halftone patterns were analyzed and the key texture parameters to be modeled by the bank were identified. Guidelines for the multiresolution texture decomposition and the model operational parameters and operational limits were established. A method for the selection of training sets based on the morphological properties of the halftone patterns was also developed. The model is fast and has the capability to continue to learn with additional training. The model can be easily implemented because it only requires a calibrated scanner. The model was tested with halftone patterns representing a range of spatial characteristics found in halftoning. Results show that the model provides accurate predictions for the tone and the spatial characteristics when modeling halftone patterns individually and it provides close approximations when modeling multiple halftone patterns simultaneously. The success of the model justifies continued research of this new printer model framework

    A Designer\u27s guide to the evaluation of digital proofs

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    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

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

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    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

    The effect of screen ruling on the saturation of pastel gamut colors

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    Reproduction of pastel colors by offset lithography produces images that have less color saturation than their continuous tone counterparts. This problem is primarily attributable to the halftone structure which approximates continuous tone pastels with large amounts of white paper and small amounts of chromatic ink. This thesis investigates the effect of screen frequency upon pastel color saturation. Single and two color overprint tints of nominal five, 10, and 15 percent printing dot areas were printed in 85, 100, 120, 133, 150, and 200 lines screen rulings. The reflectances of these colors were measured with a colorimeter and converted to CIEL*a*b* color notation to provide metric lightness and the chromatic co-ordinates from which chroma was calculated. Physical dot area was calculated by the Yule- Nielson equation for each single color patch. A more complicated graphical technique was used to find this data for the overprint colors of the same physical dot areas. For both single and overprint colors, as screen ruling becomes progressively finer, pastel saturation increased with physical dot area held constant. For this experiment, the average chroma difference at the 10 percent physical dot area between the coarsest and finest line screen ruling is 2 chroma units. This difference could also be achieved by changing physical dot area by one percent. The amount of saturation increase is dot area and hue dependent. The yellow printer showed the greatest saturation increase. The saturation increase increased with dot area for a given screen frequency. 2 Lightness decreased whenever saturation increased. When the saturation associated with the different screen rulings were compared at equal darknesses, an increase in saturation could not be statistically determined. The saturation increase from increased screen ruling at equal physical dot areas occurs because of the increased ink/light/paper interaction. Optical dot area is calculated by the Murray·Davies equation which does not compensate for this change in optical interaction. The experiment shows that at equal optical dot areas, chroma will be the same regardless of screen ruling

    Virtual electro-photographic printer model

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    A halftone image in the computer is a bitmap matrix that contains either 0 or 1 , where 0 means the printer will not deposit any toner onto a paper and 1 means the printer will deposit some amount of toner onto a paper. The amount of toner that is put by the printer onto a paper for a given input signal pattern is characterized. The hypothesis was that the distribution of toner mass on the paper for a given input matrix pattern can be modeled with a toner point spread function, a toner transfer efficiency function, and a noise function. In order to study toner mass distribution printed on paper, it is necessary to develop an analytical technique for measuring the distribution of toner mass. The analytical technique used in this thesis is an optical analysis based on light transmitted through the printed sample. This analytical technique was calibrated against a gravimetric analysis. Linear relation between the optical analysis and gravimetric analysis indicates that the technique can be used for measuring spatial distribution of printed toner mass on a micro-scale. Guided by experimental measurements of toner mass distribution, a quantitative model of the three printer functions, the spread function, the toner delivery function, and the noise function, were characterized. These functions were used to construct a printer function that was used to compare the efficiency of different halftone patterns. The result of the printer model was extended to include the optical point spread function of the paper. This provided a complete printing model that simulated both physical and optical dot gain
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