Digital Image Segmentation and On–line Print Quality Diagnostics

During the electrophotographic (EP) process for a modern laser printer, object-oriented halftoning is sometimes used which renders an input raster page with different halftone screen frequencies according to an object map; this approach can reduce the print artifacts for the smooth areas as well as preserve the fine details of a page. Object map can be directly extracted from the page description language (PDL), but most of the time, it is not correctly generated. For the first part of this thesis, we introduce a new object generation algorithm that generates an object map from scratch purely based on a raster image. The algorithm is intended for ASIC application. To achieve hardware friendliness and memory efficiency, the algorithm only buffers two strips of an image at a time for processing. A novel two-pass connected component algorithm is designed that runs through all the pixels in raster order, collect features and classify components on the fly, and recycle unused components to save memories for future strips. The algorithm is finally implemented as a C program. For 10 test pages, with the similar quality of object maps generated, the number of connected components used can be reduced by over 97% on average compared to the classic two-pass connected component which buffers a whole page of pixels. The novelty of the connected component algorithm used here for document segmentation can also be potentially used for wide variety of other applications. The second part of the thesis proposes a new way to diagnose print quality. Compared to the traditional diagnostics of print quality which prints a specially designed test page to be examined by an expert or against a user manual, our proposed system could automatically diagnose a customer’s printer without any human interference. The system relies on scanning printouts from user’s printer. Print defects such as banding, streaking, etc. will be reflected on its scanned page and can be captured by comparing to its master image; the master image is the digitally generated original from which the page is printed. Once the print quality drops below a specified acceptance criteria level, the system can notify a user of the presence of print quality issues. Among so many print defects, color fading – caused by the low toner in the cartridge – is the focus of this work. Our image processing pipeline first uses a feature based image registration algorithm to align the scanned page with the master page spatially and then calculates the color difference of different color clusters between the scanned page and the master page. At last, it will predict which cartridge is depleted

Development of a Acrylonitrile Butadiene Styrene toner for an electrophotography based additive manufacturing process

Research in to utilising electrophotography for Additive Manufacturing has been under investigation for over a decade. However, the research has been primarily focused on resolving the height limitations caused by charge accumulation and also the development of toners from tough engineering polymers. The aim of this study is to develop a suitable negatively charging engineering polymer for the Selective Laser Printing process and a more efficient method of generating toners with a suitable particle range and to assess the mechanical properties of parts produced using the toner developed through this route. The study is comprised for two parts; Chemical and Mechanical toner production. The chemical production method utilises a process, Evaporative Limited Coalescence, to produce an engineering toner in the desired 20-50μm range. It was found that during the chemical production process the negatively charging polymer was converted to charge positive. Analytical assessment of the toner was carried out to explain the change in polarity. Mechanical milling trials were also conducted under both ambient and cryogenic conditions, as well as a novel method to reduce the feed-stock material to the desired particle size range. The results suggest a significant increase in efficiency compared to prior research. Printing trials were conducted using the mechanically milled toner to assess the mechanical properties for different heating, pressure and stand-off distance conditions. It was found that, due to insufficient heating and applied pressure the final samples suffered from high porosity and poor tensile strength

Test Targets 6.0: A Collaborative effort exploring the use of scientific methods for color imaging and process control

Test Targets is a collection of scholarly papers contributed by faculty, students, and alumni of Rochester Institute of Technology. We realize the importance of having faculty set examples as authors for students to follow. We have a three-course sequence over a time span of a year to prepare students to publish their first articles when completing Tone and Color Analysis, Printing Process Control, and Advanced Color Management. In this instance, Test Targets 6.0 is a part of the course content in the Advanced Color Management course

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 Analysis of the factors influencing paper selection for books of reproduced fine art

Toner-based digital presses are now capable of matching offset lithographic presses in image and print quality. Current trends show increased interest in printing fine art books on digital presses. It is necessary to understand the extent to which digital printing systems are capable of accurately rendering fine-art reproductions. This research analyzed paper properties that maximize image quality and preference for digitally printed fine art reproductions. Four images, representing four art media, were printed on twelve papers using two digital presses. The twelve papers represented different combinations of color, print-show-through, roughness and gloss. A psychophysical experiment was conducted in which observers ranked the twelve papers for each image on the basis of image quality, color rendering quality, and surface appearance quality. The results were analyzed and a model was developed to predict the probability that a paper was ranked in the top three. Paper color (coolness), basis weight, roughness, and gloss were model parameters. Unlike gloss, roughness, and print-show-through, there was no previous metric for quantifying coolness. Therefore, an additional experiment was conducted to develop a model to predict the perception of coolness using colorimetry. An alternative experiment model was also developed that included parameters such as caliper, print gloss, line raggedness, and dot circularity. The resulting models allowed for the optimization of paper parameters that maximize the probability a paper will produce preferred and high quality images. It was concluded that the probability a book was judged as having high image quality was optimized for papers with high coolness, low roughness and low gloss. Neither print show-through, line raggedness, nor mottle were significant factors. An additional lexical analysis was performed for observer descriptions of their ranking behavior. This analysis provided complementary data to the psychophysical results. Observers\u27 descriptions of their ranking strategies did not match the rank data, suggesting a possible disconnect between observers\u27 conscious and subconscious ranking behaviors

Navigating the roadblocks to spectral color reproduction: data-efficient multi-channel imaging and spectral color management

Commercialization of spectral imaging for color reproduction will require the identification and traversal of roadblocks to its success. Among the drawbacks associated with spectral reproduction is a tremendous increase in data capture bandwidth and processing throughput. Methods are proposed for attenuating these increases with data-efficient methods based on adaptive multi-channel visible-spectrum capture and with low-dimensional approaches to spectral color management. First, concepts of adaptive spectral capture are explored. Current spectral imaging approaches require tens of camera channels although previous research has shown that five to nine channels can be sufficient for scenes limited to pre-characterized spectra. New camera systems are proposed and evaluated that incorporate adaptive features reducing capture demands to a similar few channels with the advantage that a priori information about expected scenes is not needed at the time of system design. Second, proposals are made to address problems arising from the significant increase in dimensionality within the image processing stage of a spectral image workflow. An Interim Connection Space (ICS) is proposed as a reduced dimensionality bottleneck in the processing workflow allowing support of spectral color management. In combination these investigations into data-efficient approaches improve two critical points in the spectral reproduction workflow: capture and processing. The progress reported here should help the color reproduction community appreciate that the route to data-efficient multi-channel visible spectrum imaging is passable and can be considered for many imaging modalities