Dot Gain Variation (A Study of the effects of dot gain variation to improve digital workflow for the Xeikon DCP/32D digital printing system)

Xeikon is a digital printing system that sends digital files directly to the press, thus eliminating film and plate processing. Technically, Xeikon is a web-fed press using electrophotographic technology to create information that is trans ferred to the substrate. From a marketing perspective, it is one of the preferred choices for on-demand, variable-data, and short-run printing because it has been proven to be an economical process than traditional offset. In the current printing process, the digital file is prepared as a postscript file and transferred to the Xeikon server and Xeikon Raster Image Processor (RIP) respectively. The computer section at the Xeikon RIP will RIP the file and image the information on the photoconductor drum. The information is then trans ferred to the substrate. Conventionally, the digital file can be changed to improve the tone reproduction in order to make the image suitable for each job. However, the file will be transferred back to the prepress workstation and sent back through the RIPping process. Another possible way to improve the tone reproduction of the image is the adjustment of the dot gain setting in the RIPping process without changing the native digital file. The benefits of this process could include: - Reducing the bottleneck in prepress - Minimizing prepress variables - Protecting customer file integrity Subsequently, this study examined how varying the dot gain setting in the RIPping process can improve the workflow of the Xeikon digital printing sys tem. The printed targets, produced from varying the dot gain setting at the pre press workstation (conventional workflow) and at the Xeikon RIP (proposed workflow), were compared the tone reproduction, dot gain, solid ink density, and gray balance. The time usage of each workflow was also measured. And the sample images were evaluated by a group of 20 observers. The results indicated that varying the dot gain setting at the Xeikon RIP saved the production time. Meanwhile, they showed the different output qualities in terms of tone reproduction, dot gain, and gray balance but the same in terms of solid ink density. However, the image evaluation result showed that the observers accepted images from proposed workflow rather than those from con ventional workflow

Printer Modeling for Document Imaging

The microscopic details of printing often are unnoticed by humans, but can make differences that affect machine recognition of printed text. Models of the defects introduced into images by printing can be used to improve machine recognition. A probabilistic model used to generate images showing toner placement bears similarities to actual printed images. An equation derived for the average coverage of paper by toner particles having probabilistic placement is developed using geometric probability. Simulations show that averages of ‘printed images’ do have the same average coverage as the derived average coverage equations

A File preparation tutorial to digital printing for graphic designers

Background and Significance New technologies within the printing industry open new challenges, enable innovative ways of reaching prospective clients and bring ever more stringent demands to both graphic designers and printers. Printers must implement the emerging technologies that best suit their customers and the evolving needs of the marketplace; designers must acquaint themselves with new technologies and learn to design with respect to the output device to make best use of the equipment. A short step beyond desktop technology are digital printing systems, the culmination of many technologies that have been in various stages of development for over 20 years and have finally caught up with each other. 1 Digital printers are capable of printing directly from digital information residing in an electronic file on a computer, 2 bypassing the multiple and time-consuming steps of film output, proofing, imposition and plate-making required by traditional methods. 3 As of today, digital printing is targeted to the short-run and on-demand segments of the industry. Eventually, digital approaches will apply to just every facet of graphic communication, whether it has to a run of 1,000,000 or just one. 4 Statement of The Problem The all-time myth roaming in pressrooms that designers know nothing about printing is not entirely untrue. Often, a design is finished and approved in a studio without the minimal consideration for printing and finishing. The consolidation of a digital workflow today in the printing industry increases the need for designers to acknowledge printing in their brainstorming sessions to create designs that can be produced through emerging technologies. By doing so, they can reduce problems associated with file transfer and output such as missing images and typefaces. The ease of operation of digital presses that can receive a file and print much as a desktop printer does makes them highly attractive to designers and entrepreneurs, providing these a means for printing without all the makeready procedures associated with traditional printing processes. Statement of The Project Goals The purpose of this thesis project is to evaluate the color reproduction of digital printing systems most common in industry through the creation of a universal test instrument with respect to which all the systems will be compared. The results of the test will be used to assess the capabilities of the equipment and determine their ideal applications within the graphic communications industry. A file preparation and specification guide for each of the devices tested will be compiled. The audience at which this study is targeted is graphic designers, who could benefit by learning about the advantages and disadvantages of the various systems and learning to design with these in mind. As a result, particular attention will be paid to the impact these emerging technologies have in designers\u27 approach to producing their work. This thesis project does not suggest the equipment to be tested is the best in the market place. Its results, however, may be used in determining which system is most suitable for implementation. Methodology This thesis project will provide a color reproduction evaluation and comprehensive guides for designers to prepare and expedite files to the following digital presses: Xeikon DCP-32D Indigo E-Print 1000 Xerox DocuColor 40 Heidelberg Quickmaster-DI The criterium defining the color reproduction evaluation and the elements used in the test instrument is the following: Graphic designers, the audience at which this thesis project is targeted, think in terms of memory colors; red, green, and blue. As a result, the elements comprising the test instrument will be those which designers deal with: text and images. The printed samples will be measured with a X-Rite 938 spectrodensitometer, and the results will be complemented with a visual evaluation done under standard lighting conditions. Test Instrument The test instrument will be comprised of the following: CMYK patches and bars 4-color black patches Images of different sources and resolutions Line art Type Overprinting circles Color bars RIT Neutral Balance Target for SWOP RIT 4-Color Spokes Target Evaluation Tone reproduction Solid ink density Total ink density Gray balance Dot gain Resolution Ghosting The second part to this thesis project will involve the compilation of guides to expedite files to each output device. In addition, specifications will be collected to determine the requirements for preparing variable data printing documents

Subjective Image Quality Assessment of Digitally Printed Images

Smartphones have become ingrained in our daily activities, driving their cameras to become better with every generation. As more and more images are being taken by cell phones it has become increasingly important to assess the quality of the images taken by different phones. While many cell phone images are only viewed electronically, many images also get transformed into printed images, especially photo-books, as digital printing gets better and cheaper compared to traditional printing processes. The gap between electronic image and printed image in shrinking rapidly and it becomes important to study the transition of images from screen to paper. The main goal of this research was to perform a rank order experiment for assessing cell phone image capture quality that translates to printed images via several different digital printers. It was of interest to investigate whether the overall image quality on displays correlates well with printed image quality. The important aspect was to study was to observe if there is a loss of image quality due to different digital printers

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

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

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

Potential air contaminants and noise levels generated by the Kodak Nexpress 2500 Digital Production Color press: A Study of its emissions of respirable dust, ultrafine particulates, volatile organic compounds, ozone, and occupational noise exposure

The printing industry is beginning to get acquainted with the environmental impact of digital printing technologies. This study addressed issues related to the electrophotographic dry toner printing technology used in the Kodak NexPress 2500 Digital Production Color Press. The importance of these topics will grow as high-speed variable data printing becomes pervasive, because these printed products will become widespread, and a greater number of operators will be exposed to these technologies. Indoor air quality and noise levels generated by the NexPress under normal operating conditions were studied: ventilation, dust, volatile organic compounds, ozone, and noise. The results of this study were then compared to a previous study that examined the environmental impacts of HP Indigo 3000 versus the Heidelberg Speedmaster 74. All the test results were below the permissible exposure limits of the Occupational Safety and Health Administration. The NexPress proved environmentally friendlier than the HP Indigo 3000 and the Heidelberg Speedmaster 74 in all aspects under scrutiny except for average noise exposure. The results also show that the NexPress emitted similar gas, aerosol, and noise levels regardless of print run length. This study highlights the need to develop regulations for ultrafine particulates, demonstrates how to compare environmental aspects between asymmetric printing platforms, and delivers a methodology to conduct indoor air quality and noise tests in a prominent branch of the digital printing industry

The role of paper and process technologies for mechanisms and image quality in digital electrophotography

Image quality and the mechanisms involved in digital dry toner electrophotography are influenced by the interactions between the printing machine, toner and paper in the last two steps where the paper is involved, i.e., in transferring the developed image toner to the paper, and in fusing the image to be fixed permanently on the paper surface. This study discusses the role of paper in these two steps in different technologies and its effect on the printing mechanisms and image quality. The control of optical, electrostatic and mass and heat transfer phenomena in the printing process are affected by the unevenness of the properties of paper due to its heterogeneous structure and its sensitivity to humidity conditions and printing process parameters. In this research, a set of experiments was conducted to understand the electrostatic behaviour of paper in toner transfer and thermal behaviour in toner fusing. The results show that not only image quality is affected by the variability of paper properties, but also the mechanisms of toner transfer and fusing. Accordingly, the research suggests that the paper should be included as part of the printing mechanism, performance (printability and runnability), and image quality. Consequently, if there is a change in paper properties due to a change in ambient conditions or the use of another grade for a specific application, the process parameters can be adjusted to compensate for these changes in order to meet the requirements for image quality. It was found that the variability in image quality in terms of colours (the requirement for different toner layers), grey scale (halftone structure) and the location of the image in the xy-plane is affected when rendered through the electrophotographic process. The fast mechanical speed in printing machine direction drives the toner transfer and fusing mechanisms differently from the cross machine direction. As a result, a certain image element such as a line will have different quality in these two printing directions, or if the line is placed in the length or width direction of the page. The conclusion was that the electrophotographic process should be designed to reduce or even to neglect the effect of paper when printing a high-quality colour image in a high-speed process. This can be achieved by eliminating the contact with paper from the image side in both transfer and fusing by adopting the technologies of toner jumping transfer and non-contact flash fusing. These technologies have special requirements for chemical and physical toner properties, such as modification for equal absorbance of the flash radiation by CMYK colours, a suitable melting viscosity and surface energy, and a small and narrow toner particle size and shape distribution to unify the charge-to-mass ratio of the toner, which is important for transfer quality and efficiency. To ensure high print quality for different applications, some of the transfer and fusing parameters need to be automatically adjusted according to substrate specific properties and levels of image coverage