One of the key problems in developing Enhanced and Synthetic Vision Systems is evaluating their effectiveness in enhancing human visual performance. A validated simulation of human vision would provide a means of avoiding costly and time-consuming testing of human observers. We describe an image-based simulation of human visual search, detection, and identification, and efforts to further validate
and refine this simulation. One of the advantages of an image-based simulation is that it can predict performance for exactly the same visual stimuli seen by human operators. This makes it possible to assess aspects of the imagery, such as particular types and amounts of background clutter and sensor distortions, that are not usually considered in non-image based models. We present two validation studies - one showing that the simulation accurately predicts human color discrimination, and a second showing that it produces probabilities of detection (Pd's) that closely match Blackwell-type human threshold data.
Biologically-based computer vision systems are now available that achieve robust image interpretation and automatic target recognition (ATR) performance. We describe two such systems and the reasons behind their robust performance. We also report results of three studies that demonstrate this robustness.
Holographic techniques offer a route to the generation of 3D images having all the depth cues used by the human vision system. A new electro-optic modulator system has been developed by the authors to replay dynamic holographic images. This Active Tiling (AT) system offers a route to replay giga-pixel computer generated holographic (CGH) images with video refresh rates. A key component of the AT system is an Optically Addressed Spatial Light Modulator (OASLM), onto which segments of the large pixel count CGH are loaded or written sequentially before the whole CGH frame is read out simultaneously. The OASLM device structure used consists of an amorphous silicon photosensor layer combined with surface stabilised ferroelectric liquid crystal (SSFLC) light modulation layer. A number of experiments have been conducted to determine the performance and suitability of this device for replaying a CGH. These experiments include electro-optic switching to determine the operating window and diffraction efficiency (DE) measurements to determine spatial resolution performance. A detailed description of the experimental apparatus and method used for measuring DE is presented, and results show the OASLM to be capable of diffracting light from fringe patterns with spatial periods as low as 3 micrometers (333 lp/mm). Examples of CGH replay of 3D images from the OASLM when operating within the AT system are also presented.
Continuing advances in both computing and modulator techniques and technologies increase the likelihood of electro-holography displays becoming practical in the next five years or so. These displays aim to allow high quality, interactive, 3D images to be generated from compte held dat. Until now, large pixel counts have precluded any systems of practical utility. This paper will describe recent progress towards meeting the challenges of implementing such displays. Despite more than exponential increases in computer performance, interactive hologram calculation remains an issue. A significant part of the cost of any electro-holography product will be associated with the computational requirements. These are strongly influenced by the choice of computer generated hologram (CGH) type, the algorithm used to calculate the CGH and the computer architecture chosen for implementation. The leading optics will be discussed and some experimental results presented indicating performance, cost and image quality tradeoffs. Eventual choice will depend on the specifications of the required system. Another traditional bottleneck has been the optical modulator employed. As one of the leading candidates for practical implementation, the current and projected performance of the DERA Active Tiling system will be explored, and the latest experimental results presented. These will include the first published, full parallax, true CGH, 3D image replays from an Active Tiling channel.
Advances in computing and optical modulation techniques now make it possible to anticipate the generation of near real- time, reconfigurable, high quality, three-dimensional images using holographic methods. Computer generated holography (CGH) is the only technique which holds promise of producing synthetic images having the full range of visual depth cues. These realistic images will be viewable by several users simultaneously, without the need for headtracking or special glasses. Such a data visualization tool will be key to speeding up the manufacture of new commercial and military equipment by negating the need for the production of physical 3D models in the design phase. DERA Malvern has been involved in designing and testing fixed CGH in order to understand the connection between the complexity of the CGH, the algorithms used to design them, the processes employed in their implementation and the quality of the images produced. This poster describes results from CGH containing up to 10<SUP>8</SUP> pixels. The methods used to evaluate the reconstructed images are discussed and quantitative measures of image fidelity made. An understanding of the effect of the various system parameters upon final image quality enables a study of the possible system trade-offs to be carried out. Such an understanding of CGH production and resulting image quality is key to effective implementation of a reconfigurable CGH system currently under development at DERA.
Over many years, the subject of computer generation of holograms has been visited in various guises. Historically, the obvious restrictions imposed by computational power and computer generated hologram (CGH) fabrication techniques have placed limits on what can be taken seriously in terms of image complexity. Modern advances in computational hardware and electro-optic systems now permit both the calculation and the manufacture of CGH's of complex 3D objects which fill a significant volume of space. New methods permit the recording to be made within a reasonable timescale. In addition to advancing fixed CGH generation techniques, the motivation for the work reported here includes assessment of design algorithms, modulation strategies and image quality metrics. These results are of relevance for a novel electroholography system, currently under development at DERA Malvern. This paper describes a complete process of data generation, computation, data manipulation and recording leading to practical techniques for the creation of large area CGH's. As a support to the advances in theoretical understanding and computational methods, we describe (in Part II) a new laser plotter technique that enables, in principle, an unlimited size of pixel array to be plotted efficiently with a rigorous estimate of duration of the plot run time. The results reported here are limited to 2048 X 2048 pixels. In this example, the novel switching techniques employed on the laser plotter permit the pixel array to be printed in approximately 1 hour. However, paths towards easily raising the pixel count and its associated printing rate are presented for both the computational engine and laser plotting processes.
As a support to the advances in theoretical understanding and computational methods, we describe a new laser plotter technique that enables, in principle, an unlimited size of pixel array to be plotted efficiently with a rigorous estimate of duration of the plot run time. Developments in laser plotter design are presented that allow the formation of pixellated holographic structures of high precision (c. 1 - 10 micron pixel dia.) with an accompanying high pixel count (e.g. at least up to, and beyond, 10<SUP>4</SUP> per side within a square array). The case of absorption holograms offers an easy route to a good quality result. We can then exploit the many tricks of amplitude holography borrowed from lithographic and holographic experience using ultra-fine grain silver halide materials. The problem of exposure quantization and linearization is addressed in a pragmatic fashion. The central issue of why such holograms can tolerate intrinsic diffraction artifacts within each pixel is considered along with the exposure level quantization -- it is difficult to print individual pixels within which the optical density is clinically uniform. We cannot over-estimate the reliability difficulties that can arise in a system designed to print massive arrays of pixels in a serial fashion. The electronic testing involved has to be associated with error-free repeatability and high accompanying switching speeds. This may look easy but it is the major issue that distinguishes serially printed digital holography from the simple one-step parallel process of forming the ordinary hologram.
A single beam Denisyuk reflecting holographic arrangement has been constructed using a front lit retroreflecting element and employing DuPont's OmniDex<SUP>TM</SUP> 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.
Results are presented for preliminary investigations into the way optical elements that are exposed to corrosive environments exhibit an increase in transmissive scatter the longer that such exposure exists. Near angle (i.e. < 1 degree(s)) scatter data is presented for fused silica substrates exposed to fluorine atmospheres of differing concentrations. The fluorine reacts with any water vapor present to form hydrofluoric acid which etches materials such as silica. The scatter probe wavelength used was 633 nm and scattering angles from 4 to 15 mR studied. Results are presented in bidirectional transmission distribution function (BTDF) format as well as photographs of the resulting diffraction patterns arising from passing a HeNe laser beam through the bulk of the sample which seem to show a periodic roughness profile. It is suggested that surface cleaning prior to exposure provides seeding sites, or micro scratches, for preferential attack by hydrofluoric acid.