3D threat projection has been shown to decrease the human recognition time for events, especially for a jet fighter pilot or C4I sensor operator when the advantage of realization that a hostile threat condition exists is the basis of survival. Decreased threat recognition time improves the survival rate and results from more effective presentation techniques, including the visual cue of true 3D (T3D) display. The concept of 'font' describes the approach adopted here, but whereas a 2D font comprises pixel bitmaps, a T3D font herein comprises a set of hologram bitmaps. The T3D font bitmaps are pre-computed, stored, and retrieved as needed to build images comprising symbols and/or characters. Human performance improvement, hologram generation for a T3D symbol font, projection requirements, and potential hardware implementation schemes are described. The goal is to employ computer-generated holography to create T3D depictions of a dynamic threat environments using fieldable hardware.
Electronic holographic imaging, as developed at the MIT Media Laboratory's Spatial Imaging Group, is a truly 3D real-time digital imaging medium. Recent progress in holographic video has demonstrated that the crucial technologies--computation, electronic signal manipulation, and optical modulation and scanning--may be scaled up to produce larger, more interactive, full-color holographic images. The overcoming of communication bottlenecks relies on the use of newly-developed 'diffraction-specific' computational algorithms to produce encoded holograms that are compressed by factors of about twenty to one. Here we describe progress in the very rapid 'decompression' of the holograms with stream-processor hardware built for the Cheops video processing system. The result is that 36-MB holographic images may be updated over a SCSI link in about six seconds, approaching truly interactive speed.
This report describe the hardware architecture and software implementation of a hologram computing system developed at the MIT Media Laboratory. The hologram computing employs specialized stream-processing hardware embedded in the Cheops Image Processing system--a compact, block data-flow parallel processor. A superposition stream processor performs weighted summations of arbitrary 1D basis functions. A two-step holographic computation method--called Hogel-Vector encoding--utilizes the stream processor's computational power. An array of encoded hogel vectors, generated from a 3D scene description, is rapidly decoded using the processor. The resulting 36-megabyte holographic pattern is transferred to frame- buffers and then fed to a real-time electro-holographic display, producing 3D holographic images. System performance is sufficient to generate an image volume approximately 100 mm per side in 3 seconds. The architecture is scalable over a limited range in both display size and computational power. The limitations on system scalability will be identified and solutions proposed.
Electronic holographic imaging, developed at the MIT Media Laboratory Spatial Imaging Group over the past five years, is a truly three-dimensional real-time digital imaging medium. Recent work in holographic video has demonstrated that the crucial technologies -- computation, electronic signal manipulation, and optical modulation and scanning -- may be scaled up to produce larger, more interactive, full-color holographic images. Synthetic images and images derived from real-world scenes are quickly converted into holographic fringe patterns using newly-developed `diffraction-specific' computational algorithms. A parallel- architecture signal processing system distributes the holographic video among multiple output boards. To diffract light so as to form an image in real time, the display employs an 18- parallel-channel, scanned, time-multiplexed acousto-optical modulator. The successful scaling- up of the MIT holographic video system has depended on the application of the concepts of electronic and optical parallelism at every stage.
We discuss recent developments in the MIT electronic holography display. These include the use of multiple galvanometric scanners as the horizontal scanning element, two 18-channel acousto-optic modulators (AOM's) working in tandem, and a bank of custom-designed high- bandwidth framebuffers. We also describe some recent progress on computational issues.
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.
Recent advances in both the computation and display of holographic images have enabled several firsts. Interactive display of images is now possible using the bipolar intensity computation method and a fast look-up table approach to fringe pattern generation. Full-color images have been generated by computing and displaying three color component images (red, green, and blue). Using parallelism to scale up the first generation system, images as large as 80 mm in all three dimensions have been displayed. The combination of multi-channel acousto-optic modulators and fast horizontal scanning continue to provide the basis of an effective real-time holographic display system.
Several methods of increasing the speed and simplicity
of the computation of off-axis transmission holograms are presented, with applications to the real-time display ofholographic images. The bipolar intensity approach allows for the real-valued linear summation
of interference fringes, a factor of 2 speed increase, and the elimination of image noise caused by object self-interference. An order of magnitude speed increase is obtained through the use of a precomputed look-up table containing a large array of elemental interference patterns corresponding to point source contributions from each of the possible locations in image space. Results achieved using a data-parallelsupercomputer to compute horizontal-parallaxonly holographic patterns containing six megasamples indicate that an image comprised of 10,000 points with arbitrary brightness (gray
scale) can be computed in under 1 s. Implemented on a common workstation, the look-up table approach increases computation speed by a factor of 43.
The MIT holographic video display can be converted to color by illuminating the 3 acoustic channels of the acousto-optic modulator (AOM) with laser light corresponding to the red, green, and blue parts of the visible spectrum. The wavelengths selected are 633 nm (red), 532 nm (green), and 442 nm (blue). Since the AOM is operated in the Bragg regime, each wavelength is diffracted over a different angular range, resulting in a final image in which the three color primaries do not overlap. This situation can be corrected by shifting the diffracted spatial frequencies with an holographic optical element (HOE). This HOE consisting of a single grating is placed right after the AOM in the optical setup. Calculation of the required spatial frequency for the HOE must take into account the optical activity of the TeO2 crystal used in the AOM. The HOE introduces distortions in the final image, but these are so small as to be visually negligible. The final images are of a good quality and exhibit excellent color registration. The horizontal view zone, however, diminishes for the shorter wavelengths.
Several methods of increasing the speed and simplicity of the computation of off-axis transmission holograms are presented, with applications to the real-time display of holographic images. A bipolar intensity approach enables a linear summation of interference fringes, a factor of two speed increase, and the elimination of image noise caused by object self- interference. An order of magnitude speed increase is obtained through the use of precomputed look-up tables containing a large array of elemental interference patterns corresponding to point source contributions from each of the possible locations in image space. Results achieved using a data-parallel supercomputer to compute horizontal-parallax- only holographic patterns containing 6 megasamples indicate that an image comprised of 10,000 points with arbitrary brightness (grayscale) can be computed in under one second.
Any practical holographic display device relying on the MIT synthetic aperture approach will require time-bandwidth products far exceeding those available with single channel acousto- optic modulators (AOMs). A solution to this problem is to use a multichannel AOM, thus making use of the parallelism inherent in optical systems. It is now technically feasible to accommodate a large number of acoustic channels on a single crystal with a corresponding improvement in image characteristics. The vertical view zone also becomes a significant problem for any large size display since each horizontal scan line is visible only from a narrow angle in the vertical direction. Using holographic optical elements (HOEs) alleviates this limitation in two ways: First, the interline spacing can be adjusted easily with HOEs. Second, it is possible to manufacture an HOE which will act as a one-dimensional diffuser. Placing such an HOE in the vertical focus plane of the display increases the view zone by diffusing each line in the vertical direction, but leaves the horizontal image content unaltered.
We present an electro-optical apparatus capable of displaying a computer generated hologram
(CGH) in real time. The CGH is calculated by a supercomputer, read from a fast frame buffer, and
transmitted to a high-bandwidth acousto-optic modulator (AOM). Coherent light is modulated by the
AOM and optically processed to produce a three-dimensional image with horizontal parallax.