Recent development of high resolution, full-color, full parallax digital holograms are outlined, focusing on a variety of scale-sensitive applications for this technology. This paper details recent improvements in the digital hologram resolution and recording system. The unique capabilities of digital holograms to provide solutions for a variety of applications, and some specific concepts that are being explored, are also outlined.
In the evolution of synthetic holography as a viable medium for industrial design and scientific visualization, the inclusion of full parallax represents a logical next step from the previous horizontal parallax-only approaches. The significant increase in full-parallax information content implies the need for high speed perspective view synthesis, optimized mechano-optical recording systems, and novel hologram illumination approaches. This paper outlines recording techniques for producing full-parallax holographic stereograms of computer-synthesized and acquired data. We document on-the-fly high-speed rendering software that integrates the printing and image-synthesis steps. In the interest of hologram printer size control, approaches for optical image plane enlargement are highlighted, and successful examples of A4-size (30 cm X 21 cm) full- parallax images are presented. We assess perspective-view array and image-plane pixel resolutions and their effect on overall image quality, in particular with respect to medium- size formats. Finally, we demonstrate optimized illumination techniques for controlling image clarity, including dispersion-compensated and edge-illuminated approaches.
Just as we expect holographic technology to become a more pervasive and affordable instrument of information display, so too will high fidelity force-feedback devices. We describe a testbed system which uses both of these technologies to provide simultaneous, coincident visuo- haptic spatial display of a 3D scene. The system provides the user with a stylus to probe a geometric model that is also presented visually in full parallax. The haptics apparatus is a six degree-of-freedom mechanical device with servomotors providing active force display. This device is controlled by a free-running server that simulates static geometric models with tactile and bulk material properties, all under ongoing specification by a client program. The visual display is a full parallax edge-illuminated holographic stereogram with a wide angle of view. Both simulations, haptic and visual, represent the same scene. The haptic and visual displays are carefully scaled and aligned to provide coincident display, and together they permit the user to explore the model's 3D shape, texture and compliance.
A method for producing bright full-color reflection one-step holographic stereograms using a single recording wavelength is described. The technique produces a trichromatic reseau pattern in which each column of image-plane `holographic pixels' is separated into red, green, and blue sub-columns, each of which conveys the necessary color separation information. The primary colors are produced by spatially selective pre- or post-exposure swelling of the sub- columns by the amounts needed to produce diffraction in the appropriate wavelengths. Preliminary results, produced using DuPont photopolymer Holographic Recording Film in conjunction with DuPont Color Tuning Film subjected to precisely masked ultra-violet pre- exposures, are presented. The parameters of this dry process single-laser full-color technique are discussed in the context of an automated holographic printer system.
We describe a prototype reduced-size holographic stereogram printer capable of producing scalable, Ultragram-format hardcopy output. An analysis of the resolution requirements for high quality stereogram output with respect to the printing method and printer components is presented. A holographic optical element is combined with a pseudorandom band-limited diffuser to focus the spatially modulated object beam and provide Fourier-plane broadening, thus improving image quality. We analyze issues of image preparation time and integration of image rendering and exposure control to optimize system resource requirements.
The one-step ultragram, a flexible-format computer-graphic holographic stereogram, is demonstrated in full color. Geometric limitations due to parallel diffusion screen and integral exposure planes are discussed. Image processing and translation schemes that allow for multicolor registration are demonstrated. Emphasis is placed on the pre- and post-swelling color techniques used to register color separated, predistorted component images in order to produce full-color reflection-format stereograms. Experiments using a single laser wavelength to produce a one-step white light-viewable image for each component color are presented. The wide view angle afforded by the flexible ultragram recording geometry, combined with a true color technique, is shown to result in a practical hardcopy display of three-dimensional computer-generated scenes.
We present true-color holographic stereograms made using multiple layers of Du Pont OmniDex photopolymer. Red, green, and blue color separations are reproduced at optimum replay wavelengths by exposing in blue and post-swelling using monomer color tuning films. This material is also used to record pseudo-color and true-color holograms of real-life scenes. A theoretical analysis of the color-reproduction is applied to the technique being presented and compared to results using other materials. The signal-to-noise ratio, color rendering, and color gamut area properties are shown to be comparable to those found when using dichromated gelatin and considerably better than holograms recorded in silver halide materials.
The edge-lit display format has been successfully applied to holographic stereograms. Taking advantage of the discrete nature of the information content of stereograms, the three-step production process of edge-lit rainbow holograms has been reduced to a two-step process for edge-lit holographic stereograms. Design improvements have been made to the edge-lit hologram's recording tank. The image distortion resulting from refraction as the object beam transits the air-tank interface in the final recording stage has been investigated and compensation techniques developed.
A method for producing holographic stereograms with reduced geometrical constraints is presented. The type of holographic stereogram produced, called the ULTRAGRAM, can offer a combination of large viewing zone, arbitrary viewing distance, minimal image distortion, and high spatial resolution, depending on alterable parameters in the image processing software. Computer-based image processing techniques are used to mimic the effect of optical devices while permitting simple re-configurability. The ULTRAGRAM holographic exposure apparatus can be built with reduced attention to the final viewing geometry. An astigmatic computer graphics camera design greatly simplifies image generation. The techniques described are applicable to both one and multi-step stereograms, optical predistortion methods, and both horizontal and full-parallax systems.