Modeling and Halftoning for Multichannel Printers: A Spectral Approach

Printing has been has been the major communication medium for many centuries. In the last twenty years, multichannel printing has brought new opportunities and challenges. Beside of extended colour gamut of the multichannel printer, the opportunity was presented to use a multichannel printer for ‘spectral printing’. The aim of spectral printing is typically the same as for colour printing; that is, to match input signal with printing specific ink combinations. In order to control printers so that the combination or mixture of inks results in specific colour or spectra requires a spectral reflectance printer model that estimates reflectance spectra from nominal dot coverage. The printer models have one of the key roles in accurate communication of colour to the printed media. Accordingly, this has been one of the most active research areas in printing. The research direction was toward improvement of the model accuracy, model simplicity and toward minimal resources used by the model in terms of computational power and usage of material. The contribution of the work included in the thesis is also directed toward improvement of the printer models but for the multichannel printing. The thesis is focused primarily on improving existing spectral printer models and developing a new model. In addition, the aim was to develop and implement a multichannel halftoning method which should provide with high image quality. Therefore, the research goals of the thesis were: maximal accuracy of printer models, optimal resource usage and maximal image quality of halftoning and whole spectral reproduction system. Maximal colour accuracy of a model but with the least resources used is achieved by optimizing printer model calibration process. First, estimation of the physical and optical dot gain is performed with newly proposed method and model. Second, a custom training target is estimated using the proposed new method. These two proposed methods and one proposed model were at the same time the means of optimal resource usage, both in computational time and material. The third goal was satisfied with newly proposed halftoning method for multichannel printing. This method also satisfies the goal of optimal computational time but with maintaining high image quality. When applied in spectral reproduction workflow, this halftoning reduces noise induced in an inversion of the printer model. Finally, a case study was conducted on the practical use of multichannel printers and spectral reproduction workflow. In addition to a gamut comparison in colour space, it is shown that otherwise limited reach of spectral printing could potentially be used to simulate spectra and colour of textile fabrics

Printing Beyond Color: Spectral and Specular Reproduction

For accurate printing (reproduction), two important appearance attributes to consider are color and gloss. These attributes are related to two topics focused on in this dissertation: spectral reproduction and specular (gloss) printing. In the conventional printing workflow known as the metameric printing workflow, which we use mostly nowadays, high-quality prints -- in terms of colorimetric accuracy -- can be achieved only under a predefined illuminant (i.e. an illuminant that the printing pipeline is adjusted to; e.g. daylight). While this printing workflow is useful and sufficient for many everyday purposes, in some special cases, such as artwork (e.g. painting) reproduction, security printing, accurate industrial color communication and so on, in which accurate reproduction of an original image under a variety of illumination conditions (e.g. daylight, tungsten light, museum light, etc.) is required, metameric reproduction may produce satisfactory results only with luck. Therefore, in these cases, another printing workflow, known as spectral printing pipeline must be used, with the ideal aim of illuminant-invariant match between the original image and the reproduction. In this workflow, the reproduction of spectral raw data (i.e. reflectances in the visible wavelength range), rather than reproduction of colorimetric values (colors) alone (under a predefined illuminant) is taken into account. Due to the limitations of printing systems extant, the reproduction of all reflectances is not possible even with multi-channel (multi-colorant) printers. Therefore, practical strategies are required in order to map non-reproducible reflectances into reproducible spectra and to choose appropriate combinations of printer colorants for the reproduction of the mapped reflectances. For this purpose, an approach called Spatio-Spectral Gamut Mapping and Separation, SSGMS, was proposed, which results in almost artifact-free spectral reproduction under a set of various illuminants. The quality control stage is usually the last stage in any printing pipeline. Nowadays, the quality of the printout is usually controlled only in terms of colorimetric accuracy and common printing artifacts. However, some gloss-related artifacts, such as gloss-differential (inconsistent gloss appearance across an image, caused mostly by variations in deposited ink area coverage on different spots), are ignored, because no strategy to avoid them exists. In order to avoid such gloss-related artifacts and to control the glossiness of the printout locally, three printing strategies were proposed. In general, for perceptually accurate reproduction of color and gloss appearance attributes, understanding the relationship between measured values and perceived magnitudes of these attributes is essential. There has been much research into reproduction of colors within perceptually meaningful color spaces, but little research from the gloss perspective has been carried out. Most of these studies are based on simulated display-based images (mostly with neutral colors) and do not take real objects into account. In this dissertation, three psychophysical experiments were conducted in order to investigate the relationship between measured gloss values (objective quantities) and perceived gloss magnitudes (subjective quantities) using real colored samples printed by the aforementioned proposed printing strategies. These experiments revealed that the relationship mentioned can be explained by a Power function according to Stevens' Power Law, considering almost the entire gloss range. Another psychophysical experiment was also conducted in order to investigate the interrelation between perceived surface gloss and texture, using 2.5D samples printed in two different texture types and with various gloss levels and texture elevations. According to the results of this experiment, different macroscopic texture types and levels (in terms of texture elevation) were found to influence the perceived surface gloss level slightly. No noticeable influence of surface gloss on the perceived texture level was observed, indicating texture constancy regardless of the gloss level printed. The SSGMS approach proposed for the spectral reproduction, the three printing strategies presented for gloss printing, and the results of the psychophysical experiments conducted on gloss printing and appearance can be used to improve the overall print quality in terms of color and gloss reproduction

Credulous Spectatorship from Zeuxis to Barthes

This dissertation explores intersections between trompe l\u27oeil painting and photography. It began as an interest in contemporary photographers, such as Thomas Demand, whose photographs of constructed paper models encourage viewers to discover the nature of his interventions. His strategy resonates with a centuries-old strategy in trompe l\u27oeil painting, but now in the terms of photographic, rather than pictorial presence. That is, most of Demand\u27s photographs do not compel the viewer\u27s belief in the tangible presence of the object represented; instead, they exploit photography\u27s indexical promise of delivering the world as it once appeared, in order to temporarily trick viewers about the terms of that indexical delivery. Beyond intersections in artistic strategies, I track reception accounts of trompe l\u27oeil painting and photography for their reliance on a credulous spectator. Pliny\u27s Zeuxis, who is tricked by Parrhasius\u27s painting of a curtain, remains the model for this errant credulity. In their efforts to reveal the manipulation of photographs, historians and theorists assume that the natural attitude for viewing photographs is wholly credulous and recast postmodern viewers as contemporary Zeuxises. Instead of admonishing spectators for such credulity, I argue that trompe l\u27oeil facilitates a pleasurable experience of oscillation between belief and disbelief. I also suggest that these trompe l’oeil deployments of oscillation tend to coincide with historical moments of perceived change in visual technologies—changes due to digitalization, as well as mechanical or other forms of reproduction. Trompe l\u27oeil artists play upon our supposed willingness to accept reproductions for the objects they represent. The inclusion of photographs and/or engravings in these trompe l’oeil paintings simultaneously stages and reprimands our desire for the aura of the actual object. Finally, I suggest that a contemporary renewal of trompe l\u27oeil in the medium of photography reveals an interest in recuperating belief in photographs—a belief not unlike that which Roland Barthes narrates in Camera Lucida. Just as Barthes can discover something of photography\u27s indexical promise, even after decades of his own scholarly efforts to unveil photography\u27s rhetoric of construction, so might we, even while heeding the postmodernist lessons of disbelief, recuperate a moment of belief in a skeptical age

Credulous Spectatorship from Zeuxis to Barthes

This dissertation explores intersections between trompe l\u27oeil painting and photography. It began as an interest in contemporary photographers, such as Thomas Demand, whose photographs of constructed paper models encourage viewers to discover the nature of his interventions. His strategy resonates with a centuries-old strategy in trompe l\u27oeil painting, but now in the terms of photographic, rather than pictorial presence. That is, most of Demand\u27s photographs do not compel the viewer\u27s belief in the tangible presence of the object represented; instead, they exploit photography\u27s indexical promise of delivering the world as it once appeared, in order to temporarily trick viewers about the terms of that indexical delivery. Beyond intersections in artistic strategies, I track reception accounts of trompe l\u27oeil painting and photography for their reliance on a credulous spectator. Pliny\u27s Zeuxis, who is tricked by Parrhasius\u27s painting of a curtain, remains the model for this errant credulity. In their efforts to reveal the manipulation of photographs, historians and theorists assume that the natural attitude for viewing photographs is wholly credulous and recast postmodern viewers as contemporary Zeuxises. Instead of admonishing spectators for such credulity, I argue that trompe l\u27oeil facilitates a pleasurable experience of oscillation between belief and disbelief. I also suggest that these trompe l’oeil deployments of oscillation tend to coincide with historical moments of perceived change in visual technologies—changes due to digitalization, as well as mechanical or other forms of reproduction. Trompe l\u27oeil artists play upon our supposed willingness to accept reproductions for the objects they represent. The inclusion of photographs and/or engravings in these trompe l’oeil paintings simultaneously stages and reprimands our desire for the aura of the actual object. Finally, I suggest that a contemporary renewal of trompe l\u27oeil in the medium of photography reveals an interest in recuperating belief in photographs—a belief not unlike that which Roland Barthes narrates in Camera Lucida. Just as Barthes can discover something of photography\u27s indexical promise, even after decades of his own scholarly efforts to unveil photography\u27s rhetoric of construction, so might we, even while heeding the postmodernist lessons of disbelief, recuperate a moment of belief in a skeptical age

Computer mediated colour fidelity and communication

Developments in technology have meant that computercontrolled imaging devices are becoming more powerful and more affordable. Despite their increasing prevalence, computer-aided design and desktop publishing software has failed to keep pace, leading to disappointing colour reproduction across different devices. Although there has been a recent drive to incorporate colour management functionality into modern computer systems, in general this is limited in scope and fails to properly consider the way in which colours are perceived. Furthermore, differences in viewing conditions or representation severely impede the communication of colour between groups of users. The approach proposed here is to provide WYSIWYG colour across a range of imaging devices through a combination of existing device characterisation and colour appearance modeling techniques. In addition, to further facilitate colour communication, various common colour notation systems are defined by a series of mathematical mappings. This enables both the implementation of computer-based colour atlases (which have a number of practical advantages over physical specifiers) and also the interrelation of colour represented in hitherto incompatible notations. Together with the proposed solution, details are given of a computer system which has been implemented. The system was used by textile designers for a real task. Prior to undertaking this work, designers were interviewed in order to ascertain where colour played an important role in their work and where it was found to be a problem. A summary of the findings of these interviews together with a survey of existing approaches to the problems of colour fidelity and communication in colour computer systems are also given. As background to this work, the topics of colour science and colour imaging are introduced

Images on the Move: Materiality - Networks - Formats

In contemporary society, digital images have become increasingly mobile. They are networked, shared on social media, and circulated across small and portable screens. Accordingly, the discourses of spreadability and circulation have come to supersede the focus on production, indexicality, and manipulability, which had dominated early conceptions of digital photography and film. However, the mobility of images is neither technologically nor conceptually limited to the realm of the digital. The edited volume re-examines the historical, aesthetical, and theoretical relevance of image mobility. The contributors provide a materialist account of images on the move - ranging from wired photography to postcards to streaming media

Images on the Move

In contemporary society, digital images have become increasingly mobile. They are networked, shared on social media, and circulated across small and portable screens. Accordingly, the discourses of spreadability and circulation have come to supersede the focus on production, indexicality, and manipulability, which had dominated early conceptions of digital photography and film. However, the mobility of images is neither technologically nor conceptually limited to the realm of the digital. The edited volume re-examines the historical, aesthetical, and theoretical relevance of image mobility. The contributors provide a materialist account of images on the move - ranging from wired photography to postcards to streaming media

Digital watermarking and novel security devices

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Images on the Move

In contemporary society, digital images have become increasingly mobile. They are networked, shared on social media, and circulated across small and portable screens. Accordingly, the discourses of spreadability and circulation have come to supersede the focus on production, indexicality, and manipulability, which had dominated early conceptions of digital photography and film. However, the mobility of images is neither technologically nor conceptually limited to the realm of the digital. The edited volume re-examines the historical, aesthetical, and theoretical relevance of image mobility. The contributors provide a materialist account of images on the move - ranging from wired photography to postcards to streaming media