Printing with a large number of inks, also called N -ink printing, is a challenging task. The challenges comprise spectral modeling of the printer, color separation, halftoning, and limitations of the amount of inks. Juxtaposed halftoning, a perfectly dot-off-dot halftoning method, has proved to be useful to address some of these challenges. However, for juxtaposed halftones, prediction of colors as a function of ink area coverages has not yet been fully investigated. The goal of this paper is to introduce a spectral prediction model for N -ink juxtaposed-halftone prints. As the area-coverage domain of juxtaposed inks forms a simplex, we propose a cellular subdivision of the area-coverage domain using the barycentric subdivision of simplexes. The barycentric subdivision provides algorithmically straightforward means to design and implement an N -ink color prediction model. Within the subdomain cells, the Yule-Nielsen spectral Neugebauer model is used for the spectral prediction. Our proposed model is highly accurate for prints with a large number of inks while requiring a relatively low number of calibration samples.

Secure documents often comprise an information layer that is hard to reproduce. Moiré techniques for the prevention of counterfeiting rely on the superposition of an array of transparent lines or microlenses on top of a base layer containing hidden information. Level-line moirés consist of shapes that appear to be beating upon relative translation of a revealing grating on top of a base, in which the desired information is encoded. Usually, the base only contains the information corresponding to one moiré. In order to increase the difficulty of counterfeiting, we use tessellations to incorporate two or more moirés within the same layer. With the method we propose, the information corresponding to up to seven level-line moirés can be embedded within a single base layer. The moirés are recovered with a revealer printed on a transparency or with an array of cylindrical lenses. This method is general and can be extended to other fabrication technologies.

Abstract We present a method for synthesizing high reliefs, a sculpting technique that attaches 3D objects onto a 2D surface within a limited depth range. The main challenges are the preservation of distinct scene parts by preserving depth discontinuities, the fine details of the shape, and the overall continuity of the scene. Bas relief depth compression methods such as gradient compression and depth range compression are not applicable for high relief production. Instead, our method is based on differential coordinates to bring scene elements to the relief plane while preserving depth discontinuities and surface details of the scene. We select a user‐defined number of attenuation points within the scene, attenuate these points towards the relief plane and recompute the positions of all scene elements by preserving the differential coordinates. Finally, if the desired depth range is not achieved we apply a range compression. High relief synthesis is semi‐automatic and can be controlled by user‐defined parameters to adjust the depth range, as well as the placement of the scene elements with respect to the relief plane.

We present a new approach for the reproduction of color images on a metallic substrate that look bright and colorful under specular reflection observation conditions and also look good under non-specular reflection observation conditions. We fit amounts of both the white ink and the classical cyan, magenta and yellow inks according to a formula optimizing the reproduction of colors simultaneously under specular and non-specular observation conditions. In addition, we can hide patterns such as text or graphical symbols in one viewing mode, specular or non-specular, and reveal them in the other viewing mode. We rely on the trade-off between amounts of white diffuse ink and amounts of cyan, magenta and yellow inks to control lightness in specular and in non-specular observation conditions. Further effects are grayscale images that alternate from a first image to a second independent image when tilting the print from specular to non-specular reflection observation conditions. Applications comprise art and entertainment, publicity, posters, as well as document security.

We propose a color reproduction framework for creating specularly reflecting color images printed on a metallic substrate that change hue or chroma upon in-plane rotation by 90°. This framework is based on the anisotropic dot gain of line halftones when viewed under specular reflection. The proposed framework relies on a spectral prediction model specially conceived for predicting the color of non-rotated and of 90° in-plane rotated cross-halftones formed of superpositions of horizontal and vertical cyan, magenta and yellow line halftones. Desired non-rotated and rotated image colors are mapped onto the sub-gamut allowing for the desired hue or chroma shift and then, using a 6D correspondence table, converted to optimal cross-halftone ink surface coverages. The proposed recolorization and decolorization framework is especially effective for creating surprising effects such as image parts whose hues change, or gray regions that become colorful. It can be adapted to commercial printers capable of printing with cyan, magenta and yellow inks on substrates formed by an ink attracting polymer lying on top of a metallic film layer. Applications may include art, advertisement, exhibitions and document security.

We consider the problem of obtaining a recognizable shape as superposition moiré of two line gratings. The method we propose generates moiré lines located between the shape foreground and background centers and the shape boundaries. Upon relative displacement of the superposed base- and revealing-layer gratings, the moiré lines move and give the impression of beating shapes. Original bilevel shapes are converted into elevation profiles that are embedded by small local shifts within the base-layer grating layout. The elevation profile's level lines are revealed as moiré by superposing the base and revealing layers. Similar level line moirés can be obtained by applying an identical geometric transformation to both the base and the revealing layers. In order to create grayscale or color images embedding several distinct moiré shapes, we create as base layer a dither array made of several ditherband gratings, each one embedding its specific elevation profile. Further variants include the possibility of incorporating elevation profiles within both the base and the revealing layers, or having two elevation profiles sharing a same base layer by tiling the available space. The moiré-level line techniques can be advantageously used for decorative or for anti-counterfeiting applications. Their base- and revealing-layer gratings may be produced by printing techniques, by imaging on film, or by arrays of cylindrical microlenses.

Most halftoning techniques allow screen dots to overlap. They rely on the assumption that the inks are transparent, i.e., the inks do not scatter a significant portion of the light back to the air. However, many special effect inks, such as metallic inks, iridescent inks, or pigmented inks, are not transparent. In order to create halftone images, halftone dots formed by such inks should be juxtaposed, i.e., printed side by side. We propose an efficient juxtaposed color halftoning technique for placing any desired number of colorant layers side by side without overlapping. The method uses a monochrome library of screen elements made of discrete lines with rational thicknesses. Discrete line juxtaposed color halftoning is performed efficiently by multiple accesses to the screen element library.

Today's spectral reflection prediction models are able to predict the reflection spectra of printed color images with an accuracy as high as the reproduction variability allows. However, to calibrate such models, special uniform calibration patches need to be printed. These calibration patches use space and have to be removed from the final product. The present contribution shows how to deduce the ink spreading behavior of the color halftones from spectral reflectances acquired within printed color images. Image tiles of a color as uniform as possible are selected within the printed images. The ink spreading behavior is fitted by relying on the spectral reflectances of the selected image tiles. A relevance metric specifies the impact of each ink spreading curve on the selected image tiles. These relevance metrics are used to constrain the corresponding ink spreading curves. Experiments performed on an inkjet printer demonstrate that the new constraint-based calibration of the spectral reflection prediction model performs well when predicting color halftones significantly different from the selected image tiles. For some prints, the proposed image based model calibration is more accurate than a classical calibration.

Outline font technology has long been established as the standard way to represent typefaces, allowing characters to be represented independently of print size and resolution. Although outline font technologies are mature and produce results of sufficient quality for professional printing applications, they are inherently inflexible, which presents limitations in a number of document engineering applications. In the 1990s, the topic of finding a successor to outline fonts was a hot topic of research. Unfortunately, none of the methods developed at the time were successful in replacing outline font technology and this field of research has since then declined sharply in popularity.

In message-passing parallel applications, messages are not delivered in a strict order. In most applications, the computation results and the set of messages produced during the execution should be the same for all distinct orderings of messages delivery. Finding an ordering that produces a different outcome then reveals a message race. Assuming that the partial order execution graph (POEG) capturing the causality between events is known for a reference execution, the present paper describes techniques for identifying independent sets of messages and within each set equivalent message orderings. Orderings of messages belonging to different sets may then be re-executed independently from each other, thereby reducing the number of orderings that must be tested to detect message races. We integrated the presented techniques into the dynamic parallel schedules parallelization framework, and applied our approach on an image processing, a linear algebra, and a neighborhood-dependent parallel computation. In all cases, the number of possible orderings is reduced by several orders of magnitudes. In order to further reduce this number, we describe an algorithm that generates a subset of orderings that are likely to reveal existing message races.

The present contribution aims at creating color images printed with fluorescent inks that are only visible under UV light. The considered fluorescent inks absorb light in the UV wavelength range and reemit part of it in the visible wavelength range. In contrast to normal color printing which relies on the spectral absorption of light by the inks, at low concentration fluorescent inks behave additively, i.e. their light emission spectra sum up. We first analyze to which extent different fluorescent inks can be superposed. Due to the quenching effect, at high concentrations of the fluorescent molecules, the fluorescent effect diminishes. With an ink-jet printer capable of printing pixels at reduced dot sizes, we reduce the concentration of the individual fluorescent inks and are able to create from the blue, red and greenish-yellow inks the new colorants white and magenta. In order to avoid quenching effects, we propose a color halftoning method relying on diagonally oriented pre-computed screen dots, which are printed side by side. For gamut mapping and color separation, we create a 3D representation of the fluorescent ink gamut in CIELAB space by predicting halftone fluorescent emission spectra according to the spectral Neugebauer model. Thanks to gamut mapping and juxtaposed halftoning, we create color images, which are invisible under daylight and have, under UV light, a high resemblance with the original images.

Dynamically allocating computing nodes to parallel applications is a promising technique for improving the utilization of cluster resources. We introduce the concept of dynamic efficiency which expresses the resource utilization efficiency as a function of time. We propose a simulation framework which enables predicting the dynamic efficiency of a parallel application. It relies on the DPS parallelization framework to which we add direct execution simulation capabilities. The high level flow graph description of DPS applications enables the accurate simulation of parallel applications without needing to modify the application code. Thanks to partial direct execution, simulation times and memory requirements may be reduced. In simulations under partial direct execution, the application's parallel behavior is simulated thanks to direct execution, and the duration of individual operations is obtained from a performance prediction model or from prior measurements. We verify the accuracy of our simulator by comparing the effective running time, respectively the dynamic efficiency, of parallel program executions with the running time, respectively the dynamic efficiency, predicted by the simulator. These comparisons are performed for an LU factorization application under different parallelization and dynamic node allocation strategies

Curved cross-sections extracted from medical volume images are useful for analyzing nonplanar anatomic structures such as the aorta arch or the pelvis. For visualization and for performing distance measurements, extracted surface sections need to be adequately flattened. We present two different distance preserving surface flattening methods which preserve distances according to a user-specified center of interest and according to user-specified orientations. The first method flattens surface sections by preserving distances along surface curves located within planes having a user specified constant orientation. The second method flattens surfaces along curves located within radial planes crossing the center of interest. We study and compare the properties of the two flattening methods by analyzing their distortion maps. Thanks to a multiresolution approach, we provide surface flattening at interactive rates, allowing users to displace their focus point while visualizing the resulting flattened surface. These distance preserving flattening methods provide new means of inspecting curved cross-sections extracted from medical images.

Summary form only given. Scheduling policies are proposed for parallelizing data intensive particle physics analysis applications on computer clusters. Particle physics analysis jobs require the analysis of tens of thousands of particle collision events, each event requiring typically 200ms processing time and 600KB of data. Many jobs are launched concurrently by a large number of physicists. At a first view, particle physics jobs seem to be easy to parallelize, since particle collision events can be processed independently one from another. However, since large amounts of data need to be accessed, the real challenge resides in making an efficient use of the underlying computing resources. We propose several job parallelization and scheduling policies aiming at reducing job processing times and at increasing the sustainable load of a cluster server. Since particle collision events are usually reused by several jobs, cache based job splitting strategies considerably increase cluster utilization and reduce job processing times. Compared with straightforward job scheduling on a processing form, cache based first in first out job splitting speeds up average response times by an order of magnitude and reduces job waiting times in the system's queues from hours to minutes. By scheduling the jobs out of order, according to the availability of their collision events in the node disk caches, response times are further reduced, especially at high loads. In the delayed scheduling policy, job requests are accumulated during a time period, divided into subjob requests according to a parameterizable subjob size, and scheduled at the beginning of the next time period according to the availability of their data segments within the disk node caches. Delayed scheduling sustains a load close to the maximal theoretically sustainable load of a cluster, but at the cost of longer average response times. Finally we propose an adaptive delay scheduling approach, where the scheduling delay is adapted to the current load. This last scheduling approach sustains very high loads and offers low response times at normal loads.

We propose a new powerful way of synthesizing moiré images that enables the creation of dynamically moving messages incorporating text, symbols, and color elements. Moiré images appear when superposing a base layer made of replicated base bands and a revealing layer made of a line grating comprising thin transparent lines. Each replicated base band contains the same image, e.g. text or color motifs. Since the base bands and the revealing line grating have similar periods, the revealed moiré image is the image located within each base band, enlarged along one dimension. By considering the formation of the moiré image as a line sampling process, we derive the linear transformation between the base layer and the moiré image. We obtain the geometric layout of the resulting moiré image, i.e. its orientation, size and displacement direction when moving the revealing layer on top of the base layer. Interesting moiré images can be synthesized by applying geometric transformations to both the base and the revealing layers. We propose a mathematical model describing the geometric transformation that a moiré image undergoes, when its base layer and its revealing layer are subject to different freely chosen non-linear geometric transformations. By knowing in advance the layout of a moiré image as a function of the layouts of the base layer and of the revealing layer, we are able to create moiré components running up and down at different speeds and orientations upon translation of the revealing layer. We also derive layer transformations which yield periodic moiré images despite the fact that both the base and the revealing layers are curved. By offering a new means of artistic expression, band moiré images can be used to create new designs and to synthesize visually appealing applications.

Dynamic Parallel Schedules (DPS) is a high-level framework for developing parallel applications on distributed memory computers (e.g. clusters of PCs). Its model relies on 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 are pipelined and multithreaded by construction, ensuring a maximal overlap of computations and communications. DPS applications can call parallel services exposed by other DPS applications, enabling the creation of reusable parallel components. The DPS framework relies on a C++ class library. Thanks to its dynamic nature, DPS offers new perspectives for the creation and deployment of parallel applications running on server clusters.

The extraction of planar sections from volume images is the most commonly used technique for inspecting and visualizing anatomic structures. We propose to generalize the concept of planar section to the extraction of curved cross-sections (free form surfaces). Compared with planar slices, curved cross-sections may easily follow the trajectory of tubular structures and organs such as the aorta or the colon. They may be extracted from a 3D volume, displayed as a 3D view and possibly flattened. Flattening of curved cross-sections allows to inspect spatially complex relationship between anatomic structures and their neighborhood. They also allow to carry out measurements along a specific orientation. For the purpose of facilitating the interactive specification of free form surfaces, users may navigate in real time within the body and select the slices on which the surface control points will be positioned. Immediate feedback is provided by displaying boundary curves as cylindrical markers within a 3D view composed of anatomic organs, planar slices and possibly free form surface sections. Extraction of curved surface sections is an additional service that is available online as a Java applet (http://visiblehuman.epfl.ch). It may be used as an advanced tool for exploring and teaching anatomy.

By combining a metallic ink and standard inks, one may create printed images having a dynamic appearance: an image viewed under specular reflection may be considerably different from the same image viewed under non-specular reflection. Patterns which are either dark or hidden become highlighted under specular reflection, yielding interesting visual effects. To create such images, one needs to be able to reproduce at non-specular reflection angles the same colors, by standard inks alone or in combination with a metallic ink. Accurate color prediction models need to be established which model the underlying physical phenomena in a consistent manner. To meet this challenge, we propose two models, one for predicting the reflection spectra of standard inks on coated paper and one for predicting the reflection spectra of a combination of standard inks and a metallic ink. They are enhancements of the classical Clapper-Yule model which models optical dot gain of halftone prints by taking into account lateral scattering within the paper bulk and multiple internal reflections. The models we propose also take into account physical dot gain and ink spreading for standard inks as well as the low reflectance of metallic inks at non-specular reflection angles and the poor adherence of standard inks printed on top of a metallic ink (trapping effect). These models open the way towards color separation of images to be reproduced by combining a metallic ink and standard inks. Several designs printed on an offset press demonstrate their applicability and their benefits for high-end design and security applications.

In the near future, large digital media servers are expected to offer storage capacities in the order of petabytes. Servers made of clusters of PCs connected to jukeboxes may represent an interesting alternative compared with servers made of arrays of magnetic disks. However, due to disk exchange overhead, higher seek times and lower data transfer rates, access to data located on optical disks is significantly slower than access to data located on magnetic disks. In the present contribution, we analyze the benefits and limitations of striping files across multiple optical disks in order to speedup the retrieval of large pieces of information. We also show that server applications requiring both computer power and I/O bandwidth may be distributed over several processing nodes and access files striped over multiple optical disks. For such applications, as long as disk exchanges are not necessary, a predictable speedup can be obtained by ensuring a high enough number of server computers, optical disk drive units, and enough communication bandwidth.

Abstract We propose a new service for building user‐defined 3D anatomical structures on the Web. The Web server is connected to a database storing more than 1000 3D anatomical models reconstructed from the Visible Human. Users may combine existing models as well as planar oblique slices in order to create their own structured anatomical scenes. Furthermore, they may record sequences of scene construction and visualization actions. These actions enable the server to construct high‐quality video animations, downloadable by the user. Professionals and students in anatomy, medicine and related disciplines are invited to use the server and create their own anatomical scenes. Copyright © 2002 John Wiley & Sons, Ltd.

Due to the proliferation of low-cost colour devices (digital colour cameras, scanners, printers etc.) during the last few years, colour calibration has become an important issue. Such devices should faithfully reproduce colour images, but experience shows they don't. Among the main reasons, we note the diversity of acquisition, display and printing technologies which makes standardization difficult. Each device has a different gamut, i.e. a different set of colours that it can acquire or reproduce. Furthermore, the characteristics of the devices often vary with time. Hence a calibration procedure is unavoidable for high quality colour reproduction. We give a brief overview of the colour calibration standard proposed by the International Colour Consortium (ICC), and then we present new approaches based on colour prediction models. Instead of using a large number of colour samples which must be produced and measured, only a few characteristic parameters are measured. The data corresponding to all samples are computed by a colour prediction software. This allows a quick recalibration when, for instance, the paper or the ink cartridge of a printer is changed.

A few years ago, a perceptually-tuned grayscale character generation technique was developed in order to automatically synthesize grayscale characters looking like manually-tuned pixmap characters. Weight and contrast controlled grayscale characters are obtained by grid-fitting the scaled character contours. However, this technique requires that hinting information be added to the outline font description. Adding hinting information to each outline character generally requires a considerable amount of human intervention. Our component-based parametrisable font system is a newly developed font description and reproduction technology. It incorporates for each basic character shape a software method responsible for the synthesis of an instance of that character. A given font is synthesized by providing appropriate font parameters to these character synthesis methods. Numerous concrete fonts can be derived by simply varying the parameters. Such variations offer high flexibility for synthesizing derived fonts (variations in condensation, weight and contrast) and enable saving a considerable amount of storage space. This paper shows that with component-based parametrisable fonts, high quality perceptually-tuned grayscale characters can be generated without requiring hinting information. Generating perceptually-tuned grayscale characters with parametrized component-based fonts consists in automatically adapting the phase of some of the character's parameters in respect to the underlying grid and in ensuring that thin character parts are strong enough not to disappear (weight-control).

Parallel servers for I/O and compute intensive continuous media applications are difficult to develop. A server application comprises many threads located in different address spaces as well as files striped over multiple disks located on different computers. The present contribution describes the construction of a continuous media server, the 4D beating heart slice server, based on a computer-aided parallelization tool (CAP) and on a library of parallel file system components enabling the combination of pipelined parallel disk access and processing operations. Thanks to CAP, the presented architecture is concisely described as a set of threads, operations located within the threads and flow of data and parameters (tokens) between operations. Continuous media applications are supported by allowing tokens to be suspended during a period of time specified by a user-defined function. Our target application, the 4D beating heart server supports the extraction of freely oriented slices from a 4D beating heart volume (one 3D volume per time sample). This server application requires both a high I/O throughput for accessing from disks the set of 4D sub-volumes (extents) intersecting the desired slices and a large amount of processing power to extract these slices and to resample them into the display grid. With a server configuration of 3 PCs and 24 disks, up to 7.3 slices can be delivered per second, i.e. 43 MB/s are continuously read from disks and 4.1 MB/s of slice parts are extracted, transfered to the client, merged, buffered and displayed. This performance is close to the maximal performance deliverable by the underlying hardware. The observed single stream server delay jitter varies between 0.6s (52% of maximal display rate) and 1.4s (92% of the maximal display rate). For the same resource utilization, the jitter is proportional to the number of streams that are accessed synchronously.

A multi-color dithering algorithm is proposed, which converts a barycentric combination of color intensities into a multi-color non-overlapping surface coverage. Multi-color dithering is a generalization of standard bi-level dithering. Combined with tetrahedral color separation, multi-color dithering makes it possible to print images made of a set of non-standard inks. In contrast to most previous color halftoning methods, multi-color dithering ensures by construction that the different selected basic colors are printed side by side. Multi-color dithering is applied to generate color images whose screen dots are made of artistic shapes (letters, symbols, ornaments, etc.). Two dither matrix postprocessing techniques are developed, one for enhancing the visibility of screen motives and one for the local equilibration of large dither matrices. The dither matrix equilibration process corrects disturbing local intensity variations by taking dot gain and the human visual system transfer function into account. Thanks to the combination of the presented techniques, high quality images can be produced, which incorporate at the micro level the desired artistic screens and at the macro level the full color image. Applications include designs for advertisements and posters as well as security printing. Multi-color dithering also offers new perspectives for printing with special inks, such as fluorescent and metallic inks.

We propose a new approach for developing parallel I/O- and compute-intensive applications. At a high level of abstraction, a macro data flow description describes how processing and disk access operations are combined. This high-level description (CAP) is precompiled into compilable and executable C++ source language. Parallel file system components specified by CAP are offered as reusable CAP operations. Low-level parallel file system components can, thanks to the CAP formalism, be combined with processing operations in order to yield efficient pipelined parallel I/O and compute intensive programs. The underlying parallel system is based on commodity components (PentiumPro processors, Fast Ethernet) and runs on top of WindowsNT. The CAP-based parallel program development approach is applied to the development of an I/O and processing intensive tomographic 3D image visualization application. Configurations range from a single PentiumPro I-disk system to a four PentiumPro 27-disk system. We show that performances scale well when increasing the number of processors and disks. With the largest configuration, the system is able to extract in parallel and project into the display space between three and four 512/spl times/512 images per second. The images may have any orientation and are extracted from a 100 MByte 3D tomographic image striped over the available set of disks.

Perceptually-tuned grayscale fonts are generated from character outline descriptions by applying to them a set of modifications specifically conceived for strengthening thin character parts, obtaining well-contrasted bars and preserving important relationships between character shape parts. The present study aims at comparing the legibility of perceptually-tuned grayscale and bilevel display fonts at small and very small sizes (6, 8 and 10 pt) The study confirms the results of previous studies indicating that reading speed is to a large extent independent of the typography (bilevel or grayscale) and the font size. However, perceptually-tuned grayscale characters perform better than bilevel characters for an italic string search task in a meaningless text. Regarding the subjective preferences of the test subjects, perceptually-tuned grayscale fonts at 8 and 10 point sizes received a superior rating than bilevel fonts at the same sizes.

Dither-based methods for the halftoning of images on multi-level printing devices such as multi-level inkjet printers are presented. Due to the relatively large size of single droplets, halftoning algorithms are still needed. However, since halftoning occurs between the basic levels attainable by printing one, two or several droplets at the same position, artefacts are less visible than in equal resolution bilevel printers. When dithering algorithms are used for the halftoning task, the dither threshold tiles should have oblique orientations so as to make the halftoning artifacts less visible. They should be designed so as to break up the inherent artifacts of variable dot size printers, such as for example continuous lines made up of elongated elliptic dots. The resulting visual effects are shown by simulating the printed dots of a multilevel inkjet printer.

Exact-angle superscreen dithering requires large dither tiles. Since storing precomputed screen elements for each intensity level would require too much memory, dithering must be executed on the fly at halftoning time. For this purpose a dithering coprocessor is presented which generates halftoned images at high speed. The proposed hardware architecture is based on a pipelined and scalable design which speeds up halftoning by a factor of twenty compared with modern RISC software-based solutions. We describe the architecture of the coprocessor and show to what extent it can be scaled for improving performances. The proposed coprocessor could find applications in digital color copiers which need to print scanned color images at high speed.

Presents a new approach to rendering arbitrary views of real-world 3D objects of complex shapes. We propose to represent an object by a sparse set of corresponding 2D views, and to construct any other view as a combination of these reference views. We show that this combination can be linear, assuming proximity of the views, and we suggest how the visibility of constructed points can be determined. Our approach makes it possible to avoid difficult 3D reconstruction, assuming only rendering is required. Moreover, almost no calibration of views is needed. We present preliminary results on real objects, indicating that the approach is feasible.>

Artistic screening is a new image reproduction technique incorporating freely created artistic screen elements for generating halftones.Fixed predefined dot contours associated with given intensity levels determine the screen dot shape's growing behavior.Screen dot contours associated with each intensity level are obtained by interpolation between the fixed predefined dot contours.A user-defined mapping transforms screen elements from screen element definition space to screen element rendition space.This mapping can be tuned to produce various effects such as dilatations, contractions and nonlinear deformations of the screen element grid.Discrete screen elements associated with all desired intensity levels are obtained by rasterizing the interpolated screen dot shapes in the screen element rendition space.Since both the image to be reproduced and the screen shapes can be designed independently, the design freedom offered to artists is very great.The interaction between the image to be reproduced and the screen shapes enables the creation of graphic designs of high artistic quality.Artistic screening is particularly well suited for the reproduction of images on large posters.When looked at from a short distance, the poster's screening layer may deliver its own message.Furthermore, thanks to artistic screening, both full size and microscopic letters can be incorporated into the image reproduction process.In order to avoid counterfeiting, banknotes may comprise grayscale images with intensity levels produced by microletters of varying size and shape.

Rotated dispersed-dot dither is proposed as a new dither technique for digital halftoning. It is based on the discrete one-to-one rotation of a Bayer dispersed-dot dither array. Discrete rotation has the effect of rotating and splitting a significant part of the frequency impulses present in Bayer's halftone arrays into many low-amplitude distributed impulses. The halftone patterns produced by the rotated dither method therefore incorporate fewer disturbing artifacts than the horizontal and vertical components present in most of Bayer's halftone patterns. In grayscale wedges produced by rotated dither, texture changes at consecutive gray levels are much smoother than in error diffusion or in Bayer's dispersed-dot dither methods, thereby avoiding contouring effects.

In today's digital computers, phototypesetters and printers, typographic fonts are mainly given by their outline descriptions. Outline descriptions alone do not provide any information about character parts like stems serifs, shoulders, and bowls. But, in order to produce the best looking characters at a given size on a specific printer, non-linear operations must be applied to parts of the character shape. At low-resolution, grid-fitting of character outlines is required for generating nice and regular raster characters. For this reason, grid-fitting rules called hints are added to the character description. Grid-fitting rules require as parameters certain characteristic points within the shape outlines. In order to be able to detect these characteristic points in any given input font, a topological model representing the essence of the shapes found in typographic latin typefaces is proposed. This model includes sufficient information for matching existing non-fancy outline fonts to the model description. For automatic hint generation, a table of applicable hints is added into the topological model description. After matching a given input shape to the model, hints which can be applied to the shape of the given font are taken and added to its outline description. Furthermore, a structural description of individual letter shape parts using characteristic model points can be added to the model. Such a description provides knowledge about typographic structure elements like stems, serifs and bowls.

Character rasterization on middle-resolution output devices (screens, laser printers) is one of the most difficult tasks in the domain of resolution-independent raster imaging. Low sampling leads to unacceptable low-quality discrete character shapes Better looking shapes can be generated by adapting parts of the shape outline to the sampling grid Grid adaptation of character parts is realized by several outline phase control mechanisms Algorithms have been developed to adapt horizontal and vertical bars as well as curvilinear character parts to the grid. Special phase control mechanisms are used to ensure a uniform appearance of characters over the baseline.

An original and fast filling algorithm based on vertical scan line sweep and contour tracking of a presorted shape description allows filling of character shapes with real subpixel resolution. Identical parts of a character lying at a different phase in respect to the grid will have a dissimilar discrete look. Grid constraints are applied in order to force given parts of a character (stems, serifs) to attain identical phasing. So that several contraints may be applied, degrees of freedom are provided in the form of stretchable null-segments inserted at particular locations in the character outline description. Grid constraints are also applied to avoid discrete arcs with an isolated pixel or a long horizontal or vertical run. The type of constraints applied to parts of a character consists only of horizontal or vertical subpixel translations. The resulting character description therefore remains nearly identical to the original description. The processing time used to apply grid constraints is negligible, compared with the time needed for character scan-conversion and filling. Hence, this method is very well adapted for direct character generation on non-impact printers. It is also suitable for character rasterization in typographic computer-aided design systems.

A fast raster rotation algorithm based on nearest-neighbour interpolation is described. Essentially, the computation consists of two additions/subtractions and two rounding operations per rotated image pixel. The rotation time, is about equal to the time needed for the pixelwise duplification of an image of the same size. "Nearest-neighbour" interpolation and "ideal" interpolation are compared. Because of non-linearities introduced by binary threshold operations, both interpolation functions are found to be equivalent. From spectral analysis of nearest-neighbour interpolation and from spatial analysis of rotated pixels, it is shown that image frequencies should not be higher than one quarter of the sampling rate. In order to rotate large images, an image memory management module is used for swapping transparently image blocks between main memory and disk.

This paper analyses the process of creating a printed document, which includes text processing, formatting and printing. Corresponding file formats, soft-copy generation algorithms as well as requirements of high quality graphics displays and printing systems are described. A special architecture for a printer interface system is presented which enables the high-speed generation of a document page on a printer frame-buffer, To limit mass-storage requirements, this architecture supports the generation of characters from an analytical description of their contour. Such a printer interface system has a moderate price, due to the decreasing cost of microprocessor and memory components.