We have demonstrated that 2D motion picture coding technique can be used effectively to compress the holographic fringe pattern. It is not practical to apply 2D image compression directly to the hologram because the character of the holographic fringe data is quite different from that of normal 2D images. Before the compression, we segment and transform hologram to obtain local spatial frequency spectra of the holographic fringe. These segmented spectra of the hologram become similar to a series of perspective images of the object taken by laterally moving camera. Therefore, 2D moving image compression technique, such as MPEG, can be used. Since the compression rates and image quality depend on the segmentation size and MPEG parameters, we seek the optimum condition to obtain high compression rate with small affect on image quality. We will also discuss experimental results of the relation between compression rates and image quality obtained by the proposed methods.

Three basic types of synthetic near-field hologram structures have been used for 3D-display purposes. The conventional image hologram, the holographic stereogram and the partial pixel architecture. We show that these methods are clearly related and use this result for the design of an efficient algorithm for the generation of synthetic image hologram structures.

We have been researching holographic 3D displays using a commercially available Liquid Crystal Devices (LCD). However, specifications of the LCD were not enough to holographic display, and we could obtain only small reconstructed image with the narrow viewing zone. In our present research, we are supported by an LCD manufacturer, and planning to use the custom-made LCD which has both minute and numerous pixels. The LCD's pixel pitch is 28 micrometers (horizontal) X 56 micrometers (vertical), and pixel number is 3200 X 960. Five LCDs are horizontally arranged in our electro-holographic display. By using five LCDs, total pixel number becomes about 15 Mega. We can obtain larger image and wider viewing zone compared with our previous experimental display, and can be observed binocularly. The size of the reconstructed image is 50 mm wide, 150 mm high, and 50 mm deep. Viewing zone is 65 mm at approximately 1000 mm from the image. In this display, we discard the vertical parallax and set the 1D diffuser on the vertical image plane. We also discuss the compensation of optical aberrations. Even if a single lens with large aberration is used for the optics system of the reproduction, we can obtain the reproduction image with corrected aberration by adding the compensation phase distribution to the hologram.

A holographic video imaging system with acoustooptic media, operated by a pulsed laser is described. The use of a pulse laser allows to get rid of a rotating polygon or a galvano scanner. For angular multiplexing of AOM, a specially designed combination of an acoustooptic scanner and a stripe mirror set (`still polygon') is used. The loading time of CGH data to AOM is reduced with six small size AOMs mounted in line with minimal gap. The system is capable of producing a horizontal only parallax image which is composed of 256 interlaced holographic lines. Each holographic lines has 36,000 pixels. The image is optically demagnified to the size of 7.4 X 5 cm² and changed in the rate of 60 Hz field frequency.

We have been making researches on 3D displays using computer-generated holograms (CGHs). Our CGHs are binary Fresnel holograms that reconstruct point light sources and are recorded by using high resolution laser printers (image setters). The image setters have the resolution of 3600 or 5080 dots per inch (7.1 or 5.0 micron dot width). The resolution is lower than that of photo reduction, but it has wide drawing area, and it is not expensive to draw large CGH patterns on a high contrast film. In this paper, we present an approach to making cylindrical large CGHs and hidden-point removal process. The number of reconstructible point light sources is considered to be restricted due to the low resolution of the printer. To improve this restriction and to make larger displays, we propose a method arranging plural CGHs cylindrically that reconstruct divided objects. For improving the depth of the objects reconstructed from the CGHs, we consider it is necessary to apply hidden-point removal process to our CGH calculation. Whether a certain point object is visible or not from a point of view depends on the existence of the interference fringes on the CGH plane.

In this paper the kinoform is mentioned as computer generated hologram. In the case of kinoform the fluctuation of the amplitude distribution causes the noise in the reconstructed image. Random phase distribution is added to input pattern to make the dynamic range of the amplitude of hologram pattern constant, but it is not sufficient and there seems to be speckle noise in the image. So in this paper deterministic phase coding method is applied to improve the characteristic of the reconstructed image. Animated kinoform using the image processing system with frame memory is constructed and it is displayed on the liquid crystal device. From the consideration of the characteristics of the reconstructed image we make clear the efficiency of the deterministic phase coding method for the electro-holography.

Major developments in the evolution of embossed holography are discussed in this paper. It contains brief descriptions of typical systems and techniques, as well as problems that were encountered. It is unavoidably narrow in that it represents the perspective on the author, dealing mainly with Eidetic Images. ABN Holographics, and Simian Company. All of the major processes currently used in embossed holography had been demonstrated by 1970. Yet it took another decade for embossed holography to flourish since no market materialized in spite of efforts to invent one. Then in 1981, American Bank Note purchased the rights to the Leith/Upatnieks patents, and acquired Eidetic Images, a holographics origination laboratory, as well as an embossing plant called `Old Dominion Foils'. The mating of these two acquisitions allowed product to be made almost immediately. Later developments included a hot stamp foil required for credit card holograms, a production casting system for National Geographics magazine covers, a composite (stereogram) system, and computer generated imagery. Current technology has obsoleted many of the old methods, mainly because of advances made possible by the extensive use of computers both to create the imagery and to control the hologram construction.

We describe a prototype of a full color 3D video system. The system is composed of a color liquid crystal display (LCD) panel and a special grating array, which are illuminated with a white light source. In 1995, we have proposed a method for a 3D display video system using Grating Image technique. The system is composed of an LCD and a diffraction grating array. The system can construct 3D images in real time which can be seen without any special glasses. However, the 3D images formed by the conventional system are monochromatic images. In this paper, we propose the development of a full color 3D-video system using grating image technique.

The development of the Office Holoprinter makes progress and people become interested. Discussing the possibilities one of the major concerns is the image quality. How does the quality of an one-step holograms compare with that of a traditional hologram? Can holograms made with different recording techniques be compared and if so by which means. This paper will discuss several parameters to compare different holograms and how to determine the quality.

A fabrication method for holographic stereograms using a large liquid crystal display panel (LCD) is proposed and experimental results are described. Holographic stereogram is a useful method that can synthesize computer graphics or portraits of 2D perspectives but its process is troublesome. An LCD of a lap top personal computer is applied for perspective display. This method has some advantages, e.g., simple optical layout, no registration mechanism, no aberration by projection lenses and so on. A technique to improve the quality of holograms with a holographic optical element is also proposed.

The subjects of display holograms tend to fall into 3 categories--those which aspire to replicate their real world counterparts, those which through the conventions of graphics, text or diagrams represent abstract information and those which record holographic phenomena of subjects. In designing a holographic shrine for a Catholic Church in Australia the modes of representation available through the history of art and their bearing on holographic image types were examined. The most highly symbolic elements of the image were recorded by interferometric techniques in order that they appeared to be made only from light and darkness. To enable the viewer to make a transition from perception to reverie it was necessary for the scale of the image to encourage z axis eye movement. This experiences of staring into space, was achieved by leading attention from near to far ground objects along the omnidirectional segments of a highly embellished geodesic dome. Links between near and far ground objects were made through the use of darkness, in particular by the intentional overexposure of several hundred live flowers which form part of the dome texture. The combination of replication of material objects and holographic phenomena produce a non literal conjunction which stimulates a contemplative response in the viewer.

The ICVision system provides the functional equivalent of a real-time holographic stereogram. Using diffractive optics, the system creates a set of discrete viewing regions called virtual viewing slits. Each pixel of the display fills each viewing slit with different image data. When the images presented in two virtual viewing slits separated by an interoccular distance are filled with stereoscopic pair images, the observer sees a 3D image. The images are computed so that a different stereo pair is presented each time the viewer moves approximately 1 eye pupil diameter (approximately 3 mm), thus providing a series of stereo views. The current embodiment of the ICVision display is realized by integrating a diffractive optical element with a conventional AMLCD. The authors have previously reported on the design of static displays and real-time monochromatic full motion displays. This paper discusses the design details of a full color display. The current system does not require the use of color filters within the AMLCD. A portable version of the real-time color display will be demonstrated at the conference.

The problems in recording, copying and reconstruction of color transmission and reflection holograms are discussed with respect to the following source laser parameters: (a) a set of RGB (red, green, blue) wavelengths, (b) spectral bandwidth (temporal coherence), (c) spatial coherence, and (d) output power. The analysis of different optical schemes for color holography with referring to the parameters mentioned above suggests the necessity of having various lasers with different spatial, temporal and power characteristics. Based on the analysis, solid-state lasers with intracavity as well as extracavity frequency conversion examined as an efficient source of RGB (red, green, blue)--wavelengths under various operating regimes: CW, quasi-CW (with high repetition rate--up to 1,000 kHz), pulse, Q-switch, mode-locking etc. The possible optical schemes of such lasers are proposed and their parameters are discussed.

The performance of an electro-holographic display has been limited by space and spatial bandwidth of spatial light modulators. This paper presents a new type 3D display using numerous small-size light sources. The concept of the display is based on the electro- holographic display using acousto-optic devices. Each light source is aligned on a circle at narrow intervals, and its output beam is focused on the center of the circle. Its focal point or the image of its focal point is scanned by the mechanical X-Y scanner, and each light's intensity is modulated by each parallax image of the viewing angle. This display can produce big-and-natural 3D images with high resolution and high refresh-rate.

The e-beam lithography commonly used in the semiconductor industry is used to create large format grating image holograms. Delicate and bright images with extremely fine features can be generated using this newly developed method. In this paper, a quantitative and qualitative analysis related to the grating image hologram is discussed in detail. Using the optimized condition derived based on the quantitative analysis, the e-beam lithography technique commonly used to generate semiconductor masks has been implemented to create images with extremely fine features. The optimized condition together with the simplistic nature of the grating written to the image, the grating image holograms generated will be bright and colorful under white light illumination. The above mentioned generic characteristics plus the optimized condition obtained from our analysis make the e-beam lithography technique a versatile and powerful method in creating image holograms. High end products such as kinegrams can be easily implemented by using this technique. Furthermore, kinegrams with extremely fine features to generate a continuous and smooth imaging effect can be effectively created by this newly developed technique. The orientation and the pitch of the grating written to the grating image hologram determines two important characteristics of the grating image. More specifically, the grating orientation determines the viewing angle while the grating pitch determines the color projected to the viewer. As the grating image hologram is typically being illuminated by an inclined incident white light, the incident light beams will be diffracted into a colorful curved surface extending from the illuminated grating pixel. Taking a realistic extended illuminating light source into consideration, a single grating pixel actually will diffract the illuminating light cone into a colorful surface ensemble. With this understanding, it is possible for us to design the grating image hologram using the colorful surface ensemble as one of the design parameters available to us. In other words, we can use the colorful surface ensemble to shape the final image created by illuminating the grating image hologram with prespecific extended white light conditions. Two grating image holograms, one of which is a 5 by 5 centimeters square grating and the other a 3.5 centimeters by 2 centimeters elliptical kinegram, were successfully created by utilizing the analysis mentioned above. It was discovered that the limitation of the field size available to today's e-beam machine poses an important design consideration. That is, when field stitching is required to create a large area grating image hologram, the images being written should be carefully chosen so as to minimize the mismatch effect among the junction of each field. The two newly completed holograms showed that with the design methodology presented in this article, high quality large area grating image holograms can be created.

A display system requiring no special glasses is a useful technology for 3D images. The lenticular display system has such defects that it has a non-planar screen and views a blur. In this paper, a newly developed, 3D real-time display with a HOE is described. This simple 3D display can improve above-mentioned problems. And the advantage of the screen HOE is that the number of presented views is much greater that of an equivalent lenticular display, because the screen HOE can multiplex pixels both horizontally and vertically to display lateral views. This screen HOE can be made more easily and smoothly. The trial screen HOE is 4' X 5' and consists of 128,000 holograms. Therefore, the image size measures approximately 4' X 5', and the resolution is 200 X 160 pixels X 4 views.

Methods similar to those used to describe light-in-flight recordings can be used to interpret a great number of optical phenomena such as conventional interferometry, reflection, diffraction, holographic interferometry, Doppler effects, Fermat's principle of least time, Heisenberg's uncertainty principle, apparent super luminal velocities in outer space and relativistic optical effects.

The research `Solaris', tests the reliability of holographic materials intended for outdoor use in the fields of architecture, public art and advertising. It demonstrates the damage that can be caused to the materials through exposure to ultraviolet light, heat and humidity, and proposes solutions employing laminating techniques or chemical processes. As a result, we are now able to make spatial and temporal use of sunlight, so as to convey ideas and virtual images in open- air public spaces.

Holography is now featured regularly on the Internet, particular on the World Wide Web (WWW) which provides text, still and animated graphics, video and sound information on an ever expanding catalogue of subjects to an ever expanding audience of users. During the last year the number of holography sites on the WWW has increased rapidly and now includes institutions, private individuals, commercial holography companies, publishers and enthusiasts. Is what they provide useful and are there any major benefits to this system which could not be achieved with more traditional methods of communication? A review of several holography sites is provided, a case study of the development of one of those sites is given in detail and an extensive reference list of WWW addresses is included.

A single beam Denisyuk reflecting holographic arrangement has been constructed using a front lit retroreflecting element and employing DuPont's OmniDex^TM photopolymer as the holographic recording film (HRF). The light from an advanced (extended coherence) argon ion laser operating at 514 nm is allowed to pass through the substrate/photopolymer onto the surface of the reflector and reflect back to the photopolymer, the HRF thus acting as an intelligent beamsplitter. Because of the self-limiting, self-developing nature of the HRF, the hologram is processed quickly in situ without the need for wet processing and the space between the retroreflector and photopolymer is thus rendered interferometrically active with high intrinsic accuracy. Results will be given of how this simple arrangement can give high contrast fringes due to phase changes in air caused by the passage of high speed projectiles. A high speed CCD framing camera has provided the means of capturing sequential images of events with exposure time down to a few nanoseconds. The interferometer plays a dual role acting as an interferometer or as a schlieren system.

The design and fabrication procedures of two types of high frequency DOE's: (a) sub- wavelength pulse width modulated DOE's destined for use in an optical switching system and (b) inclined high frequency gratings for an optical backplane interconnection are reviewed.

A special type of 3D holographic imaging is considered. In this case object wave that is filtered by a horizontal slit is split into two identical components with the help of a diffraction grating that is positioned just ahead of a thick-layered light-sensitive material. It is shown that the 3D pattern formed as a result of the recording of the interference of the mentioned components of the object wave reveals the property of reconstructing the 3D image of the object when being illuminated by the light scattered by a diffusing screen. Such a type of the recording is referred to as reference-free selectogram. The results of the experiments on the reference-free selectogram recording are presented. Two types of thick-layered light-sensitive materials were used in the experiments: reoxan and dichromated gelatin. The material reoxan presents a polymer matrix (1 mm thick) in which an anthracene compound sensitizer and oxygen are dissolved. The dichromated gelatin presents a jelly that has been sealed between two glasses. The thickness of the light-sensitive layer varies from 1 mm to 3 mm in this case.

Color holograms are recorded on silver halide emulsion using multiple wavelengths. The images are reconstructed without shifts in wavelengths. This allows applications in three areas of holography: (a) display holograms yield images that closely resemble the original objects. (b) In holographic interferometry where no prior information is available concerning the locations of zero displacements, there has not been a convenient method which allows the determination of the locations of the zeroth order interference fringes. Using color holography, these fringes appear in white color; thus are automatically identified. (c) Holographic optical elements created using this method greatly enhance operations where multiple wavelengths are involved.

The artist outlines several of his image-making techniques in holography. Using the work `Event Horizon' as an example, he describes the master set-up as well as the white light transmission set-up that was used in the making of this art work. Specifically the design and use of Holographic Optical Elements and imperfect collimating lenses in the mastering steps are discussed.

This paper presents two rather specific applications of holographic interferometry. The first is related to the study of displacements and strains associated with the rapid (200 meter/second) crack propagation in pressurized polymer pipes. Denisyuk type holography using a double pulsed Ruby laser was found to yield practical results; due to the rather explosive nature, experiments were carried out at night, outside of the classical buildings. The other series of tests is concerned with the localization of most stressed zones in prototypes manufactured from steel castings. As the use of brittle lacquers is now prohibited, holographic interferometry was used to find the locations for putting the strain gauges. Relatively large (up to 1 X 1 m) and heavy (about 700 kgs) castings were tested, resting on an unisolated concrete slab, using a semi-professional ESPI system and a small argon laser.

In this paper we present the results of analytical examination of long pipe oscillations. The study performed the characteristics of the oscillations, based on solution of a system of the wave equations for surface displacement. The pipe under the consideration is an elastic cylindrical shell. The oscillations are initiated by an externally applied loading force, that has a form of short-acting pulse. The results obtained are compared with experimental data from interferometric analysis of a 6m long polymer pipe. Keywords: holographic non-destructive testing, oscillation analysis.

We present an off-axis transmission holographic technique for recording marine plankton in situ within a test tank of 36,000 ml with a pulsed laser in a 40 ns interval. The holographic plate is located in air and is therefore unaffected by aquatic conditions that may cause emulsion degradation (e.g. non-uniform swelling and surface contamination). The reference beam traverses a path in air only, and thus remains unaffected by dense concentrations of plankton. Third order aberrations, notably spherical aberration and astigmatism, are suppressed to yield an experimental resolution of 7 lp/mm (70 micrometers ) with a USAF 1951 target located 600 mm in water from the observation window. Plankton particle counts examined by real image reconstruction show a strong correlation with duplicate samples examined under a microscope.

This paper will discuss projects that have been completed based on results of fabrication techniques and accelerated aging tests which expand the range of design applications possible with embossed materials. Installation of this value added material on a permanent or semi- permanent basis also makes it economically feasible to include dedicated illumination systems which bring out the full spectral potential of these materials.

We recently have presented a real-time holographic interferometer using sillenite crystals connected with phase-shifting for quantitative measurement of diffuse objects deformations. In our basic set-up, the crystal, sandwiched between two polarizers, is set in front of the optical head and followed by a CCD camera with an imaging objective. With this system, for conventional objects and using 2.2 Watts of Ar3+ laser power 512 nm, interferograms can be observed on object fields of about 30 cm X 20 cm (crystal size 1 cm X 1 cm and 26 mm objective focal length). In this paper we present investigations to increase the observed field in the existing system and to be able to use lower power lasers. Since setting the object at larger distances should lead to an unsufficient luminous level for hologram recording, we have proceeded by different ways. First, we use shorter focal length objective, giving a larger field- of-view, and larger crystals have to be used in this case to avoid vignetting. Second, we use a large aperture frontal objective in order to collect more light and that images the object on the crystal, the final image being observed through relay imagery.

In several important applications of holography such as optical information storage it is necessary to multiplex several functions or many optical components in the same thin film recording material. An optically recorded multiple grating hologram can be encoded either sequentially or simultaneously, but for the same total exposure, the diffraction efficiency of sequentially recorded holograms is lower than for a simultaneous hologram. If the number of multiplexed gratings is increased, and the angles between these gratings are reduced, the recorded object beam should resemble the field from a diffuse-object. However, in actual holograms, noise is present and it seriously limits that density. That is why maximum storage density is a function of the hologram's signal-to-noise ratio (SNR). For all of these reasons it is important to analyze the characteristics of diffuse-object holograms in the field of information storage. In this communication we present experimental results on the influence of the number of object waves and their spatial distribution on diffraction efficiency and SNR for bleached holograms recorded by using a collimated reference wave and N divergent object waves. The N object waves are interfered with the reference wave by using a simultaneous recording (coherent recording).

Traditional star charts have several major problems that prevent them from reaching their full potential as educational tools. These include, most notably, opacity and the parallax problem,the solutions of which would make possible a more useful optical device that would permit the viewing of both the real stars and a projected image of the stars at infinity, with instructive labels, simultaneously and superimposed. A holographic star chart is such a device. We pursued two different approaches to this concept.

An encoding method, random phase-coded multiplexing, was applied to the volume hologram multiplexing and demonstrated the recording of 100 holograms in a LiNbO₃:0.01% Fe. The multiplexing method is simple because the encoding material is just a ground glass. A theory was also developed to interpret the properties of the method.

Holographic Interferometry has been successfully employed to characterize the materials and behavior of diverse types of structures under stress. Specialized variations of this technology have also been applied to define dynamic and vibration related structural behavior. Such applications of holographic technique offer some of the most effective methods of modal and dynamic analysis available. The technology is non-destructive, real-time, and definitive in allowing the identification of vibrational modes, displacements, and motion geometry. Structures and processed materials can be analyzed with very low amplitude excitation and the resultant data can be used to adjust the accuracy of mathematically derived structural models. Holographic Interferometry has offered a powerful tool to aid in the primary engineering and development of advanced complex composite materials. One such material is a graphite-epoxy fiber reinforced polymer matrix composite. This type of material is finding increased use in advanced aerodynamic, automotive, and other highly mobile platforms. Avionic and undersea applications must consider environments where extremes in vibration and mechanical stresses can affect both operation and structural stability. These are ideal requisites for analysis using advanced time-average holographic methods in the initial design and subsequent test of such advanced structures and materials. Holographic methods are non-destructive, real-time, and definitive in allowing the identification of vibrational modes, displacements, and motion geometries. Such information is often crucial to the determination of mechanical configurations and designs as well as operational parameters of structures composed of advanced engineering materials.

If pathological specimens are preserved by a method known as plastination, they are rigid enough to be imaged with continuous beam lasers on a conventional holography table.

A technique and device for recording and copying reflection holograms (Denisyuk's holograms) with a semiconductor laser, emitting in the visible spectral range ((lambda) equals 672 nm), are described. Superfine-grain silver halide materials HP-650 are utilized, ensuring high values of the diffraction efficiency without bleaching after development. The major operating characteristics are determined and the possibility of holographic recording of real objects with vertical and horizontal positioning is demonstrated. The technique and device can find application in the realization of replicas of museum items, unique and rare specimens in the premises where they are stored without the need of transporting them to the holographic laboratory.

We report some results of theoretical analysis and experimental study of selective properties of 3D holographic grating. In particular, the case of strong deviation of the propagation vector of the reconstructing wave from Bragg conditions by tuning the wavelength and/or the angle of the incident illuminating beam is considered. In this case, it is more convenient, to operate with joint function of angular-spectral selectivity. The character of this joint function should be taken into consideration, if true color holographic images are of interest. Key words: angular and spectral selectivity, 3D reflection grating, diffraction efficiency.

In digital holography, computation of holograms is often reduced to calculations of fast Fourier transforms if the distance between the object plane and the hologram plane is large enough. Two classical approximations for solving this problem include a binomial series expansion of the distance and an elimination of the so-called inclination factor. We present here a vectorial algorithm which computes the discrete form of the light propagation equation obtained by the Huygens' principle for a bidimensional object. None of the approximations mentioned above have been used. This enables the computation of a diffraction pattern at any distance compatible with the scalar theory of diffraction. This vectorial algorithm has been implemented on workstations, on a Convex C-220 and on a Cray YMP computer. We focus our attention on the computing granularity of the problem and we present processing times and the associated performances for bidimensional images. Various holograms are computed and compared with those obtained by two traditional methods, namely, Fresnel transforms and the resolution of the rigorous scalar diffraction equation using discrete convolutions. We then consider the 3D case and modifications are proposed in order to parallelize this algorithm.

A new method with one wavelength laser for making 3D diffuse objects true color rainbow hologram on photoresist plate is presented. In this method, we have used the synthesized slit technology to record the true color rainbow hologram H₂. It results in a higher energy utilization. Otherwise, it is also easy to control the color reproduction of the reconstructing image. About the advantages mean it is of value in fabricating 3D diffuse objects true color embossed rainbow hologram. A satisfactory experimental result is obtained and the theory analysis is given.

A new method of precisely measuring the radius of curvature of the divergent spherical and cylindrical wavefront of a laser beam is presented by the use of a holographic grating and an optical system, the measuring accuracy is analyzed and some measures of improving the result are given. Finally, the possibility of measuring the distortion aberration of an optical system by the use of a non-linear holographic grating is also discussed.

An optical pickup system for optical disc drives utilizes optical elements for information signal detection, focus-error detection and track-error detection. We propose an optical pickup using double holographic lenses--replacing conventional optical elements for focus-error detection and track-error detection--to reduce the pickup size. There are two important requirements when using holograms for an optical pickup. One is to compensate for chromatic aberration caused by laser diode wavelength deviation, and the other is to obtain an appropriate beam spot size for focus-error detection. To meet these requirements, we used double holograms, where one has divergent power and the other convergent power. By optimizing the double hologram pattern, the optical system is achromatized. We observed the achromatic effect, 0.07 (lambda) (RMS) for a laser diode wavelength change of +/- 10 nm. The beam position error was less than +/- 1 micrometers . We reduced the NA of the system to give a relatively large spot beam and a large depth of focus.

We have developed a head-up display (HUD) using a holographic combiner. A HUD superimposes information in front of the driver. The HUD must be unaffected by sunlight and should be small. A holographic combiner eliminates the VFD wash-out, and compensates for the distortion of concave mirror. The size of unit is reduced by folding the optical path. The image distance is extended to 1.2 m by using a powered element. The dimensions of the HUD unit is 155 X 135 X 77 mm, and the thickness of the optical unit is 40 mm.

We propose a modification to the process of error-diffused quantization often used for printing computer-generated holograms on bitonal devices. The output of many devices (e.g. laser printers) consists of `dots' printed at locations on a fixed grid. The printed patterns often are modeled as ideal square pixels. However, real dots typically are more round than square, and often overlap adjacent pixels. These variations can affect the quality of the reconstructed hologram significantly.