Research

The Peripheral Systems Lab creates and explores new paradigms in color imaging. The main focus is directed towards novel imaging such as spectral color prediction models, wide gamut color prints, metallic prints, artistic imaging, and the creation and modellization of moiré phenomena. The theory finds applications in various fields, from special print reproduction techniques to new anticounterfeiting methods.

Colour Reproduction and document protection
We have developed several spectral prediction and ink spreading models for predicting the spectra of classical color halftone patches. They work well for offset prints, thermal transfer and ink-jet printers. These models take into account the most important physical phenomena such as surface reflections, internal Fresnel reflections at the paper-air interface, light propagation within the paper bulk and ink spreading. Very high prediction accuracies were obtained thanks to the modellization of the superposition dependent spreading of ink dots.

Applications include the prediction of ink thickness variations in color halftone prints as well as new document protection features. Theses anti-counterfeiting elements comprise images with hidden patterns printed with classical and metallic inks which become visible only under specular reflections. [Hersch et al.03]. Spectral prediction models were also useful for creating fluorescent images visible only under UV light [Hersch et al.07]. Current efforts include the development of prediction models for prints on metallic substrates as well new fluorescent imaging applications.
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The Moiré theory  and applications
A thorough Fourier-based model of the moiré phenomenon has been established, which can be used for both the analysis and synthesis of moiré effects. It provides a full qualitative and quantitative understanding of the moiré effect and has been applied to document authentication and anti-counterfeiting. Main results are published in the book, The Theory of the Moiré Phenomenon, volumes I et II , by I. Amidror (Springer) as well as in the paper by Hersch and Chosson [2004] . Main applications comprise the protection of security documents with one-dimensional moiré images.
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Microstructure Imaging
Microstructure imaging enables synthesizing images incorporating visually appealing microstructures. Microstructures are graphic objects specially designed to convey their own message. The microstructure encrustation techniques we have developed rely on the automatic creation of dither matrices or on chromatic color differences [Rudaz04]. Microstructures can be seen by the naked eye, by a magnifying glass or as a moiré revealed by a dot screen or a micro-lens array. Microstructures are being used by the industry for producing remotely printable secure event entry and travel tickets.
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Parallelization framework & Visible Human Server
We created a framework for facilitating the development of parallel applications on PC clusters [Gerlach03]. This framework allows to define dynamic parallel schedules DPS, which support compositional customizable split-compute-merge graphs of operations (directed acyclic flow graphs). The graphs and the mapping of operations to processing nodes are specified dynamically at runtime. DPS applications can call parallel services exposed by other DPS applications, enabling the creation of reusable parallel components. Applications include the Visible Human Server running on PCs offering real-time slicing [Gerlach02], anatomic organ construction and visualization [Evesque02] as well as the specification, extraction and flattening of curved surfaces [Saroul03].
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Digital typography
Methods were developed for the generation of perceptually-tuned grayscale characters improving the readability of LCD displays. Methods have also been created for generating typographic characters made of parametrisable components. The component-based font synthesizing system enables generating fonts with variations in condensation, weight and contrast [Hu01]. Since fonts are merely described by parameters, they require an order of magnitude less storage space than conventional outline based font descriptions. The book Visual and technical Aspects of Type gives information about various typographic issues.
Publications