We describe a new kind of bistable nematic display where bistability is achieved by a field induced surface anchoring transition. The system uses simple planar anchorings with different strengths. The system is intrinsically fast, with a writing response time in the 30 microseconds range on the order of 20 V pulses, and a contrast on the order of 10. We describe the physics of coupled field induced anchoring transitions which explains these properties.

The observation of the growth with time of chiral C* nuclei (domains) in the surrounding chiral nematic melt is presented for ferroelectric substances possessing the first order phase transition chiral nematic N* - chiral smectic C*, which is characterized by a strong jump of the tilt angle at the phase transition temperature. For the first time we report the observations of ferroelectric domains, having a 'screw' shape in the cell bulk; the domains grow much faster along the screw axis than across it. The screw pitch is appreciably larger than the helix pitch in the C* phase: the axis of the intrinsic helix turned out to be parallel to the screw axis. Both the screw- and the helix pitches were observed by optical microscopy. We provide a model, giving our interpretation of the phenomenon, based on the fundamental properties of the ferroelectric smectic C* phase at interfaces with various media. It was shown earlier that, due to the specific features of the surface tension of the ferroelectric smectic material, the smectic layers must be inclined with respect to the surface normal, and such an inclination is a function of the material parameters (for instance, the piezoelectric modulus), of the interface parameters (for instance, the anchoring strength) and of the temperature. In fact, the inclination of the smectic layers is related to the appearance of dislocation nets and depends on the interface anisotropy. We describe the growth of the smectic C*/N* interface, which is stabilized by free ions, decreasing the surface tension due to the neutralization of the polarization charges. The estimates of the inclination angle and of the ratio between the screw- and the intrinsic helix pitch are given.

Porous matrices with determined structure, pore shape, size, and volume fraction, impregnated with liquid crystals (LC) can be used as model systems to understand physical properties of dispersed LC-materials important for display applications. Using dielectric spectroscopy, static and dynamic light scattering we have investigated equilibrium and dynamic properties of LC dispersed in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different pore sizes. The spatial confinement and the existence of a highly developed interface in porous matrices have the strong influence on dielectric and optical properties of LC which resulted in the appearance of a low frequency relaxational process (f less than or equal to 10 KHz) absent in bulk and a strong modification of modes due to the molecular rotation around short axis and librational motion. All observed relaxational processes in confined LC are not frozen even at temperatures about 20 degrees below the bulk crystallization temperature. One of the new properties among others observed for nematic LC confined to porous matrices is the appearance of slow relaxational process which does not exist in the bulk LC and wide spectrum of relaxation times (10^-8 - 10)s.

We theoretically investigate topological constraints and the defect structure around a spherical body immersed in a uniform nematic liquid crystal. Depending on the strength of anchoring on the particle surface, there are three possibilities. At rigid anchoring WR/K >> 1, the inner surface constraint forces a disclination ring of a radius at approximately 1.2*R, with R the particle size. At a lower, critical value W* the disclination rings contracts to the surface and, for small anchoring, WR/K << 1, the director distribution is regular, defect-free.

The market of television displays is an area of outstanding economical importance due to its annual production volume of more than 100 million TV tubes. Fifteen million TV sets were produced in Western Europe in 1993 alone. On the other hand the materials used in the tubes and the energy consumption for production and during operation are issues of great ecological importance. It is therefore of social and political interest to achieve simpler and ecologically compatible solutions through new technologies and innovative technical concepts. Displays with a diagonal of one meter or more for TV and computer monitor applications operating in accordance with HDTV or higher formats require technology that is either not available or too costly. Conventional television tubes would not only have to be very large, the high internal pressure would entail an extraordinary mechanical stability of the tube, resulting in a notable increase in weight. Flat LC-displays present another alternative. Today as in the near future, only high performance color LCDs with relatively small physical dimensions are produced due to the complex technology involved. Furthermore, there are technical inadequacies when it comes to brightness and contrast in daylight or under oblique viewing angles. There are no solutions in the offing for these problems. A third possibility is the enlarged projection of pictures produced either by LCDs or similar techniques. In this case daylight projection can also pose problems due to the lack in definition and brightness. The most promising technique for a high brightness, high definition and large area displays are based on the direct projection with laser beams. Presently unsatisfying solutions are available for 2 basic parts of this technique: the low-cost laser sources needed for a color TV projection and the simple deflection system delivering the required number of pixels. There is a world-wide effort concerning the development of suitable light sources. We propose the development of a deflection system based on a novel simple electro-optical deflector fabricated in LiNbO₃.

Possibilities of creating a spatial-temporal light modulator (STLM) with matrix electrodes using energy reflection coefficient modulator at the glass-LC boundary have been studied. Ferroelectric smectic C* which as the optical structural angle between the director and the normal to the smectic layer near 45 degrees is proposed as an LC-medium. The results of investigation make it possible to construct an LC-valve characterized by high transmission (approximately equals 90%) of nonpolarized light in a wide spectrum range in the open state.

Several new liquid crystal operation modes for direct-view and projection display are reviewed. Both transmissive and reflective types are considered. In the transmissive mode, we describe chiral-homeotropic cell for high contrast direct-view displays and a polarization recombination method for high brightness projection displays. In the reflective mode, we describe mixed-mode twisted nematic cells for direct-view displays and an improved 45 degree twisted nematic cell for projection displays.

We have summarized some of the most important progress and status in STN and TFT/LCDs since 1995. This progress includes the introduction of large SVGA and XGA color STN panels; fast (4 msec) STN; in-plane-switching wide viewing angle color XGA TFT panels; introduction of large SVGA and XGA color TFT panels; the introduction of small-size high- resolution TFT panels; and the realization of fast inspection method for production line LC alignment inspection. Current investment status and production capability are also summarized.

Present-day displays are essentially linear optical elements to control light. Influx of ideas and approaches between display sciences and nonlinear optics is taking place recently. In the report, we discuss situations where achievements of nonlinear optics can be applied to the development of liquid crystal display principles. Particularly, we discuss new principles of control of the slope of director reorientation induced by electric fields, bistability in tilted electric fields, and photoinduced orientation.

The method which allows us to increase the time interval during which an element is 'on,' using twist or S-effect in nematic-photosemiconductor structure is considered. The basis of this consideration is now that this structure exhibits the effect of memory in definite conditions. The memory organization is based on the hysteresis loop existence in an LC having a high Friedericksz threshold value.

Studied luminescence characteristics of the new materials for the electroluminescence displays and optical storage devices. Optically stimulated luminescence in CaO:Eu,Sm and MgO:Eu,Sm have been studied. On optically stimulating a UV treated sample, the trapped electrons are released by Sm²⁺ ions and are recaptured by Eu³⁺ ions leading to the luminescence which is characteristic of Eu emission.

The demand for accurate color reproduction has never been as high as today. Not only in the high-end electronic prepress market, but also in the desktop publishing and home office markets, the availability of both input and output devices is increasing rapidly. Most of the input devices today capture positive originals: scanners capture either reflective or transmissive originals; digital cameras are capable of capturing real life scenes as well. In some market segments (such as, e.g., the newspaper environment), there also is a definite interest in scanning negative originals. Especially with the new emerging APS standard for film (where manual manipulation of the film strips is no longer necessary), the demand for negative scanning will also increase in the home office market. Scanning negatives, however, is a very delicate process. Not only the input device should be characterized properly, but also the negative film itself is a parameter which needs to be studied carefully. On negative film, the information is stored inverted and due to the color dye layers within the negative film, there also is a density shift between the red, green and blue planes. The main problem, however, is caused by the fact that, due to the variations in the development process, the characteristics of a strip of developed negative film can differ considerably from other strips of the same film type. In this paper, we first give a brief survey of our approach to scanning negatives presented in the past. Then, we show how the unpredictable properties of negative films can cause this approach to fail and discuss some substantial improvements. In this respect, we show how the adaptive approach taken in the conventional photofinishing environment can be used electronically. In a following section, we describe how the inverted positive image data can be transformed into a well-known, calibrated color space. In the last section, we briefly discuss the minimal requirements for an ideal negative scanner.

Digital printing is described as a tool to replace conventional printing machines completely. Still this goal was not reached until now with any of the digital printing technologies to be described in the paper. Productivity and costs are still the main parameters and are not really solved until now. Quality in digital printing is no problem anymore. Definition of digital printing is to transfer digital datas directly on the paper surface. This step can be carried out directly or with the use of an intermediate image carrier. Keywords in digital printing are: computer- to-press; erasable image carrier; image carrier with memory. Digital printing is also the logical development of the new digital area as it is pointed out in Nicholas Negropotes book 'Being Digital' and also the answer to networking and Internet technologies. Creating images text and color in one country and publishing the datas in another country or continent is the main advantage. Printing on demand another big advantage and last but not least personalization the last big advantage. Costs and being able to coop with this new world of prepress technology is the biggest disadvantage. Therefore the very optimistic growth rates for the next few years are really nonexistent. The development of complete new markets is too slow and the replacing of old markets is too small.

The accuracy of today's color management systems fails to satisfy the requirements of the graphic arts market. A first explanation for this is that color calibration charts on which these systems rely, because of print technical reasons, are subject to color deviations and inconsistencies. A second reason is that colorimetry describes the human visual perception of color differences and has no direct relation to the rendering technology itself of a proofing or printing device. The author explains that only firm process control of the many parameters in offset printing by means of a system as for example EUROSTANDARD System Brunner, can lead to accurate and consistent calibration of scanner, display, proof and print. The same principles hold for the quality management of digital presses.

The development of networked, distributed, digital color printing gives rise to new requirements of managing color. In the paper, platform for automatic, source and device independent color correction is defined and its implementation outlined. Moreover, a model for capacity in distributed digital printing is presented.

The paper is investigating different paper grades and their properties as whiteness, color, absorbency, smoothness and them method how ink, toner or colorants are applied to the paper surface. The influence on the output color accuracy is discussed and it is pointed out which paper properties are influencing color accuracy and which properties are neutral. Different color printer technologies as electrophotography, ink jet and thermo are combined with the paper parameters.

Digital graphical systems, color copiers and their increasing technology have forced the security printing industry to drastically change the ideas about security structures. Complex guilloches, screen traps, etc. do no longer provide sufficient protection and techniques based on limitations of these digital systems, like limited color reproduction or loss of certain gradation levels, are becoming more and more useless as the technology in both hard- and software moves on. A closer study of the problem immediately reveals that for both human perception and digital scanning we are dealing with signal-processing in two dimensions. The different frequency bands that are important in security design are explained and security structures are classified according to these bands. It appears that in security design we are dealing with four frequency bands: visual band, sample band, alias band and upper band. An important observation is that printed security structures, carried out in the frequency band of human perception (i.e. visible structures) do not protect against digital scanning, so protective structures must be of a higher frequency level. Some machine detectable copying security structures are treated according to their different frequency band classification. The basic idea behind the treated structures is to add to a security design some kind of modulation in the upper part of, or above the visual frequency band. With both screen angle modulation (SAM) and micro screen angle modulation ((mu) SAM) the orientation of screen lines is used as modulation, whereas with sample band image coding (SABIC) essentially we have some kind of 'screen-in-screen' modulation. Both techniques satisfy the two major conditions that have to be fulfilled for effective protection of security documents, i.e. they have to be easy to print and easy to detect.

All the steps in the imaging chain -- from handling the originals in the prepress to outputting them on any device - - have to be well calibrated and adjusted to each other, in order to reproduce color images in a desktop environment as accurate as possible according to the original. Today most of the steps in the prepress production are digital and therefore it is realistic to believe that the color reproduction can be well controlled. This is true thanks to the last years development of fast, cost effective scanners, digital sources and digital proofing devices not the least. It is likely to believe that well defined tools and methods to control this imaging flow will lead to large cost and time savings as well as increased overall image quality. Until now, there has been a lack of good, reliable, easy-to- use systems (e.g. hardware, software, documentation, training and support) in an extent that has made them accessible to the large group of users of graphic arts production systems. This paper provides an overview of the existing solutions to manage colors in a digital pre-press environment. Their benefits and limitations are discussed as well as how they affect the production workflow and organization. The difference between a color controlled environment and one that is not is explained.

Color mixing by a halftoning process, as used for color reproduction in graphic arts and many forms of digital hardcopy, is neither additive nor subtractive. Halftone color reproduction with a given set of primary colors is heavily influenced not only by the colorimetric properties of the full-tone primaries, but also by effects such as optical and physical dot gain and the halftone geometry. By computer simulations based on basic spectrophotometric measurements on actual prints, we demonstrate that such effects not only distort the transfer characteristics of the process, but also have an impact on the size of the color gamut. In particular, a large dot gain, which is commonly regarded as an unwanted distortion, expands the color gamut quite considerably. We also present an image processing model that can describe and quantify the effects of physical and optical dot gain on different media and with different halftoning methods.

The color classification applied for large documents requires simple color transformations that enables the implementation of high speed algorithms with reasonable performance. The use of HSV and HSL color spaces in such applications is limited due to their perceptual non- linearity, even if these spaces are attractive due to the simplicity of their definition and transformation. This paper proposes new relationships of the HSL and HSV color spaces based on the replacement of the lightness and brightness definitions, with new relationships based on more perceptual lightness and brightness. The new HSL and HSV color spaces are visualized in three dimensions and the shapes are compared with the old regulate spaces. These spaces remain device dependent as the conventional HSV and HSL spaces, but the distribution of color is more suitable for some application like color clusterization. The new defined color spaces are asymmetric. It is shown how the new HSV and HSL color spaces simplify and improve the accuracy of a clusterization process. The results of clusterization process are compared in the processed image area as well as in the 3D histogram diagram. The color spaces are used for clusterization of colormaps, with application to automatic color classification in large documents (maps, blueprint documents, etc.). Results of clusterization process for blueprint documents are provided for the new introduced HSL and HSV color spaces.

The nature, purpose and data presentation features of media jobs are analyzed in relation to the content, document, process and resource management in media production. Formats are the natural way of presenting, collecting and storing information, contents, document components and final documents. The state of the art and the trends in the media formats and production data are reviewed. The types and the amount of production data are listed, e.g. events, schedules, product descriptions, reports, visual support, quality, process states and color data. The data exchange must be vendor-neutral. Adequate infrastructure and system architecture are defined for production and media data. The roles of open servers and intranets are evaluated and their potential roles as future solutions are anticipated. The press frontend is the part of print media production where large files dominate. The new output alternatives, i.e. film recorders, direct plate output (CTP and CTP-on-press) and digital, plateless printing lines need new workflow tools and very efficient file and format management. The paper analyzes the capture, formatting and storing of job files and respective production data, such as the event logs of the processes. Intranet, browsers, Java applets and open web severs will be used to capture production data, especially where intranets are used anyhow, or where several companies are networked to plan, design and use documents and printed products. The user aspects of installing intranets is stressed since there are numerous more traditional and more dedicated networking solutions on the market.

In order to render clouds and represent the distribution of the light int a cloudy sky, a new rendering method for cloudy skies is introduced. In our new method, clouds are represented by a layer called C layer. Three attributes named transparence, reflection and shadow parameter, are additionally defined at each point of the C layer, and these attributes are used to simulate the translucence and the shading effects of clouds. The atmospheric aerosol such as haze or fog is assumed to have a uniform density under the C layer, and introduce an efficient approach to calculate the scattering coefficient by the haze at different densities according to the vision range.

The creation of training, expert and similar systems, using databases of complex color images, is a dream of many specialists in various subject matter areas including medicine. However, so far there has not been solved the problem high-quality metrological input to a computer of complex color images. This problem is now being solved mainly in two directions: (1) creation of black-and-white high-resolution hardware with alternate photographing an object through R, G, B-filters and subsequent superposing three images upon each other; (2) creation of high- resolution color hardware. It should be noted, besides purely engineering problems, with the resolution degree, the cost for the black-and-white equipment grows, in fact, quadratically and, that for the color hardware rises more than cubical. At the same time, in inputting static objects, one more possibility exists, namely: successive input of separate fragments of a complex image with subsequent mathematical joining (sewing together) them in a computer. Here the effective resolution of hardware used heightens such number times, that is practically proportional to the number of fragments input, except common zones required for high-quality joining. The present work is dedicated to practical realization of the latter direction conformingly to the input of cell group images. It should be noted that, all the three directions have to develop and complement each other, since even today the requirements for the images quality specified by specialists remains subjective enough and, permanently increasing demands lie within restricting frames (those technical, financial, etc.).

Screening is perhaps the oldest form of image processing. The word refers to the mechanical cross line screens that were used at the beginning of this century for the purpose of photomechanical reproduction. Later on, these mechanical screens were replaced by photographic contact screens that enabled significantly improved process control. In the early eighties, the optical screening on graphic arts scanners was replaced by a combination of laser optics and electronic screening. The algorithms, however, were still digital implementations of the original optical methods. The printing needs in the fast growing computer and software industry gave birth to a number of alternative printing technologies such as electrophotographic and inkjet printing. Originally these deices were only designed for printing text, but soon people started experimenting and using them for printing images. The relatively low spatial resolutions of these new devices however made complete review of 'the screening issue' necessary to achieve an acceptable image quality. In this paper a number of recent developments in screening technology are summarized. Special attention is given to the interaction that exists between a halftone screen and the printing devices on which they are rendered including the color mixing behavior. Improved screening techniques are presented that take advantage of modeling the physical behavior of the rendering device.

Changing demands in advertising and printing business has made the digital press systems valid competitors to offset technology for specific markets. Whereas offset is still superior in quality and high volume printing, the time consuming and costly prepress activities, as well as the need for huge investments in the press, make the all-in-one formula very attractive. How to link a fast/cheap machine with decent output-quality, making use of electrophotography? We use electrophotography as a pretext for making a stability analysis of several halftoning systems. As shown in a previous article (Ref. 3) we use the Fourier characteristics to figure out its dependence. In a first introduction we point out why electrophotography brings us to this matter. The further outline of the article scans through a list of opposite screening systems where we focus on the color stability in function of registration.

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. Error-diffusion in color space is also appropriate for multi-level halftoning. Visual artifacts can be reduced by introducing dot over dot color inhibiting constraints.

This talk describes a modification to the standard error diffusion algorithm that results in a more homogeneous response in the dark and light image regions. This is achieved using a dynamic threshold imprint function that depends on the input image and the binarized output pixel.

A new approach for hardcopy reconstruction of volumetric objects of arbitrary shape and material/density characteristics is proposed. It is based on the extension of bi-level or halftoning approximation techniques to 3D signals representing digital volumetric objects of varying material density such as human skeleton hardcopy reconstructions made from a sequence of tomographic slices. Three-dimensional halftoning algorithms are used in conjunction with 3D additive bi-level fabrication techniques such as those used in a stereolithographic apparatus.

For portable printers low energy consumption of the printhead is important. Because of their high efficiency shear-type piezo printheads are the best choice. However, when scaling down the dimensions the effects of crosstalk between two adjacent channels become increasingly visible. In order to study the interaction of different channels a simple linear model was developed. The model includes the mechanical characteristics of the actuators and some general coupling elements between the actuators. Due to the simplicity of the model a 360 dots per inch printhead with 64 nozzles could be simulated as a whole. A set of parameters was determined from crosstalk measurements so that the output values of the model fitted the measured values. The results are in good agreement with the measurements. The model was helpful in finding a means to compensate pattern-dependent velocity deviations by adjusting the control pulse, allowing the complete elimination of crosstalk effects. With a second pulse parameter the refill time of a channel was minimized for all patterns. Hence the firing frequency of the printhead was increased to 8 kHz. The velocity deviations due to crosstalk are less than 5%.

The electronic pre-press industry has undergone a very rapid evolution over the past decade, driven by the accelerating performance of desktop computers and affordable application software for image manipulation, page layout and color separation. These have been supported by the steady development of colo scanners, digital cameras, proof printers, RIPs and image setters, all of which make the process of reproducing color images in print easier than ever before. But is color print itself in decline as a medium? New channels of delivery for digital color images include CD-ROM, wideband networks and the Internet, with soft-copy screen display competing with hard-copy print for applications ranging from corporate brochures to home shopping. Present indications are that the most enduring of the graphic arts skills in the new multimedia world will be image rendering and production control rather than those related to photographic film and ink on paper.

Avionics head up and helmet mounted displays have severe demands on luminance and resolution. There is a requirement to view the display over a range of ambient illumination from full sunlight to night and to provide high accuracy for weapon release. Installation constraints further complicate the optical design and mass is crucial for the head mounted hardware. Currently, the only display device that can meet these demands is the monochrome cathode ray tube (CRT). This paper explores the potential for replacing the CRT with a flat panel device (FPD). The problem areas such as installation, illumination and drive are discussed and the suitability of various flat panel technologies is considered. The potential for color is also reviewed. The paper is intended as an introduction to the application and future papers will address achievements as development progresses.

Smiths Industries has been involved in the design, manufacture and supply of products used for the presentation of information, in one form or another, from its early pioneering years through to the present day. In the mid 1980s Smiths Industries began to invest in the then emerging active matrix liquid crystal display (AMLCD) technology which the company believed would eventually take over from the cathode ray tube. To date Smiths Industries has made a significant investment in acquiring the enabling technology needed to produce active matrix liquid crystal color head- down displays for fast jet, helicopter and civil aircraft applications. The significant improvement in AMLCD product quality and manufacturing capability over recent years has enabled market penetration of AMLCD technology products to be achieved in military and civil avionic markets. Virtually all new contracts for head-down displays are now demanding the use of AMLCD technology rather than the cathode ray tube. A significant decision to move to AMLCD technology was made by McDonnell Douglas Helicopters in 1995, when a contract to supply over 4000 head-down display products for the Apache Helicopter was let. This has paved the way for the future of AMLCD technology.

This paper describes an experiment conducted to investigate the type of display symbology that most effectively conveys height information to users of head-down plan-view radar displays. The experiment also investigated the use of multiple information sources (redundancy) in the design of such displays. Subjects were presented with eight different height display formats. These formats were constructed from a control, and/or one, two, or three sources of redundant information. The three formats were letter coding, analogue scaling, and toggling (spatially switching the position of the height information from above to below the aircraft symbol). Subjects were required to indicate altitude awareness via a four-key, forced-choice keyboard response. Error scores and response times were taken as performance measures. There were three main findings. First, there was a significant performance advantage when the altitude information was presented above and below the symbol to aid the representation of height information. Second, the analogue scale, a line whose length indicated altitude, proved significantly detrimental to performance. Finally, no relationship was found between the number of redundant information sources employed and performance. The implications for future aircraft and displays are discussed in relation to current aircraft tactical displays and in the context of perceptual psychological theory.

There are many potential uses of helmet-mounted displays (HMDs). One is to allow aircrew to spend increased time off- boresight scanning the outside world for threats or targets. Another is for acquiring a target and subsequently employing a weapon whilst looking off-boresight. An experiment was conducted to examine the use of HMDs for both these tasks using four different attitude displays: pitch ladder, cylinder, arc segmented attitude reference and roll-pitch. The task involved subjects flying a simulated low-level, high-speed mission which was divided into two phases. Phase one required subjects to scan off-boresight for air threats and acquire them by using the off-boresight capability of the HMD. Phase two required subjects to use the head-down display (HDD) to locate ground targets and use the HMD off- boresight capability to acquire them. Novel objective performance measures, designed specifically to evaluate HMD symbology, were collected. Overall, it was found that performance was superior when using the pitch ladder than other displays. This was supported by the subjective findings that it provided higher situational awareness than other displays. It was concluded that the advantage for the pitch ladder may have been due to having the same symbology on the HUD and HMD, enhancing smooth transitioning between the two displays. The importance of developing operationally relevant tasks and measures for the evaluation of HMDs are discussed and the implications of this research for future work are considered.

New methods to measure information uptake and eye strain have been developed. The speed of information uptake is measured with a reading task that demands quick and accurate eyemovements. Accommodative facility is shown to be a good measure for eye strain. A standard monitor and three types of HMDs were compared on both tasks. The HMDs were (1) binocular and immersive, (2) monocular and see-through, and (3) monocular and see-around. These HMD types find applications in virtual environments, the cockpit, and solider modernization respectively. Reading performance was measured while the subject was stationary and during head motion. From the experimental results rules of thumb for the use and design of HMDs are derived.

Helmet mounted displays are now widely accepted as an essential component of any head coupled night vision system and due to enter service on several rotary wing and fast jet aircraft. The technologies and human factors issues involved in the design and manufacture of HMDs are now reaching maturity. However the operational effectiveness of HMDs is greatly influenced by the design of the HMD system as a whole. This paper presents a discussion of HMD system design issues, covering the design of HMDs for both night and day applications, system architectures and helmet tracker subsystems. The paper then presents an overview of an HMD system which provides both night and day operational capability as part of a head coupled system.

The traditional 'graphic arts' market has changed very rapidly. It has been only ten years now since Aldus introduced its 'PageMaker' software for text and layout. The platform used was Apple-Mac, which became also the standard for many other graphic applications. The so-called high-end workstations disappeared. This was the start for what later was called: the desk top publishing revolution. At the same time, image scanning became also user-friendly and heavy duty scanners were reduced to desktop-size. Color- reproduction became a commodity product. Since then, the pre-press industry has been going through a technical nightmare, trying to keep up with the digital explosion. One after another, tasks and crafts of pre-press were being transformed by digital technologies. New technologies in this field came almost too fast for many people to adapt. The next digital revolution will be for the commercial printers. All the reasons are explained later in this document. There is now a definite need for a different business-strategy and a new positioning in the electronic media-world. Niches have to be located for new graphic arts- applications. Electronic services to-and-from originators' and executors environments became a requirement. Data can now flow on-line between the printer and the originator of the job. It is no longer the pre-press shop who is controlling this. In many cases, electronic data goes between the print-buyer or agency and the printer. High power communication-systems with accepted standard color- management are transforming the printer, and more particularly, the pre-press shop fatally. The new digital printing market, now in the beginning of its expected full expansion, has to do with growing requests coming from agencies and other print-buyers for: (1) short-run printing; (2) print-on-demand approximately in-time; (3) personalization or other forms of customization; (4) quick turnaround.

The paper describes an algorithm for multi-spectral images segmentation that takes into account the shape of the clusters formed by the pixels of the same object in the spectral space. The expected shape of the clusters is based on the dichromatic reflection model, and its extension for optically homogeneous materials. Further the influence of the illumination and image formation by a color CCD camera are considered. Based on expected shape of clusters we propose a criterion of similarity/homogeneity for the extended region merging algorithm. This criterion works successfully in case of objects of voluntary shape and illumination by one or several sources of the same spectrum.

In this article we present the study of a color edge extractor operator. We make an evaluation of the costs in terms of die size and latency time in the case of an implementation in F.P.G.A. This makes it possible to operate at 25 images/second and thus satisfy a lot of industrial applications.

Multimedia's goal can be defined as enhanced information transfer using an optimized stimulation of the human perceptual system. This can be realized by technology producing combined acoustical, visual and somatosensory stimulations of various kinds. Currently, the main effort is in the refinement of the technology to produce high-quality stimulations. However this is not sufficient by itself to produce optimal stimulation of human perception at its higher levels. We present some issues and solutions underlying this problem, in particular the selection of the stimuli for a given application.

Human visual system is well suited for reliable and adequate volumic perception of natural environment. Volumic data flows coming from outer physical space are easily acquired in real time. Current modes of imitating physical spaces or creating of hypothetical virtual spaces have a lot of drawbacks. The quality and the speed of volumic data presentation are severely limited. Moreover most of current devices destined to operate with artificially generated volumic data flows seem poorly compatible with eye/brian data processing procedures. It can be illustrated for example by multiple failures in introduction of public stereoscopic TV in spite of numerous lengthy efforts made for years since the appearance of TV. Thus quite novel approaches must be formulated and novel principles introduced. Unified concept of volumic imaging of artificially generated data is introduced here. This concept gives way to creation of principally novel prospective devices which might drastically enhance authenticity of perceived artificially generated data. Quite novel principle of 'one-eyed' volumic imaging system for robotics is proposed.

Healthcare is a major candidate for improvement in vision of the kinds of information societies that are now being visualized. The concept of telemedicine captures much of what is developing in terms of technology implementation especially if it is combined with the growth of high performance computing (HPC), the Internet and the World Wide Web. EUROMED is a European Commission funded three year project beginning with phase I in January 1996. The overall aim of EUROMED is to collaboratively exploit, combine and support HPC activities to enhance and standardize visualization techniques to be used in telemedicine applications throughout Europe. Firstly, EUROMED will create a hierarchial telemedicine network throughout Europe and ex- Soviet Union countries linking isolated medical sites with specialized clinics and HPCN centers. Secondly, EUROMED will develop a hierarchical telemedical visualization suite of packages incorporating, superimposing and enhancing presently used image modalities such as CT, MRI, angiography, PET and SPECT and newer techniques such as ultrasound diffraction tomography. Thirdly, EUROMED will utilize the WWW and its tools to combine the telemedicine network and the visualization suite in a complementary manner to existing medical facilities.

In the optical part of a virtual reality system often an exit pupil is used that is larger than the entrance pupil of the eye. However, a system with a small exit pupil could have several advantages: more efficient use of light, less accommodation/convergence conflict, better optical quality, and a larger angular image field. To see under which conditions one can benefit from these advantages, we examine two possible drawbacks of using a small exit pupil, one related to the loss in image quality at exit pupil decentration and the other related to the limitations in the freedom of movement of the eye. An optical system with a small exit pupil, preferably a little larger than 1 mm in diameter, is only feasible, if a combination of eye-tracker and exit pupil shifting mechanism is implemented.

Since virtual environments (VE) have facilitated new dimensions of human-computer-interaction, many applications have been realized. The drawback of these complex applications is the difficulty to control all interactions only visually. This report describes the interaction with an additional human perceptive channel: the haptic perceptive channel. Haptic means the kinesthetic sense of force and the tactile sense. With haptic displays, or haptic devices, a user perceives computer-simulated forces or tactile stimulation. Important aspects of human haptic perception based upon experiments are described. Furthermore, haptic displays, developed in research labs, and their applications are illustrated.

Virtual reality (VR) is known as one of the most exciting computer-related technologies. Although its definition is still vague among experts, it is expected that a VR system should give the user an experience of being 'immersed' in a synthesized environment. Aims of this deeper level of user immersion range from the look-like of the scenes where realistic rendering is one of the goals (vision stimulus), to interaction paradigms through the use of, e.g., dataglove peripherals type, to acoustics (earring stimulus) trying to merge as much as possible the human senses towards the desired immersion. Attempting to increase the previously mentioned realism, an extra sensorial perception is recalled and the user is exposed to the feeling of 'virtual comfort' by means of a new parameter: the temperature. The obtained results concentrate on interaction paradigms and couple input/output feedback, emphasizing the factor 'presence.' The prototype, although conceptually simple, brings together within a couple of virtual scenarios, a software/hardware solution, so far original in this field.

Taking into consideration the importance of color perception for human visual function, ergophthalmology considers it from a position of two points of view. Color vision itself is of significance to a number of professions, which require sharp, precise and stable color perception. At the same time, color vision represents the sensitive index for evaluation of eye retina, function of which it is. In this work we shall discuss the second approach only. This paper is devoted to description of our own method of retinal function examination during the working activity by means of measuring the time of following color contrast. The results of using this method in operators VDU in industrial conditions are given as well. These data are of interest for physiology of vision and also such applied sciences as labor physiology and ergonomics. Simultaneously they may be considered from a position of the science of color and correspondingly to display sciences.

The colorimetric characterization of computer-controlled CRT displays require radiometric measurements with high precision and accuracy. Most of the available color- measuring-instruments (either photometers, colorimeter and especially spectroradiometers) use expensive optical and electronical devices, which make them nearly unaffordable in many applications. The aim of this paper is to present a low-cost design of a colorimeter with regard to the maximum achievable accuracy.

In this paper, we present the efficient voting classifier for the recognition of handwritten and printed characters. This system consists of three voting nonlinear classifiers: two of them based on the multilayer perceptron, and one uses the moments method. The combination of these kinds of systems shows superiority of neural techniques applied with classical against exclusive traditional approach and results in high percentage of correctly recognized characters. Also, we present a comparison of the recognition results.

For the compression of color images, the lossy compression standard JPEG has two major shortcomings. Firstly, it codes the color components separately. This reduces the possible compression ratio. Secondly, the image quality at very low bit rate is seriously degraded by blocking artifacts. The paper describes an extension of an existing segmented image coding (SIC) method for monochrome images to images containing a limited number of colors. The new technique codes the colors more efficiently and performs better at high compression. After conversion to the YUV color space, the corresponding luminance image is compressed using monochrome SIC. At the decoder, this image is reconstructed and the gray-values are translated into colors. Because different colors in the image can have the same gray-values and because SIC is lossy, some gray-values may be wrongly reconstructed in the decompressed image. To prevent the introduction of foreign colors in a region, i.e. colors which are not present in the region in the original image, bit vectors are constructed indicating which colors are present. The decoder uses this information to replace foreign colors by colors of the region. The bit vectors are compressed using a lossless bi-level coding scheme. The paper presents experimental results which show that the new method produces a much better subjective image quality than JPEG at high compression due to the absence of block distortion.