Michael Halle

Conformal surface parameterization for texture mapping

We give an explicit method for mapping any simply connected surface onto the sphere in a manner which preserves angles. This technique relies on certain conformal mappings from differential geometry. Our method provides a new way to automatically assign texture coordinates to complex undulating surfaces. We demonstrate a finite element method that can be used to apply our mapping technique to a triangulated geometric description of a surface.

Autostereoscopic displays and computer graphics

Autostereoscopic displays present a three-dimensional image to a viewer without the need for glasses or other encumbering viewing aids. Three classes of autostereoscopic displays are described: reimaging displays, volumetric displays, and parallax displays. Reimaging displays reproject an existing three-dimensional object to a new location or depth. Volumetric displays illuminate points in a spatial volume. Parallax displays emit directionally-varying image information into the viewing zone. Parallax displays are the most common autostereoscopic displays and are most compatible with computer graphics. Different display technologies of the three types are described. Computer graphics techniques useful for three-dimensional image generation are outlined.

The Complete Survey of Outflows in Perseus

We present a study on the impact of molecular outflows in the Perseus molecular cloud complex using the COMPLETE Survey large-scale 12CO(1-0) and 13CO(1-0) maps. We used three-dimensional isosurface models generated in right ascension-declination-velocity space to visualize the maps. This rendering of the molecular line data allowed for a rapid and efficient way to search for molecular outflows over a large (~16 deg2) area. Our outflow-searching technique detected previously known molecular outflows as well as new candidate outflows. Most of these new outflow-related high-velocity features lie in regions that have been poorly studied before. These new outflow candidates more than double the amount of outflow mass, momentum, and kinetic energy in the Perseus cloud complex. Our results indicate that outflows have significant impact on the environment immediately surrounding localized regions of active star formation, but lack the energy needed to feed the observed turbulence in the entire Perseus complex. This implies that other energy sources, in addition to protostellar outflows, are responsible for turbulence on a global cloud scale in Perseus. We studied the impact of outflows in six regions with active star formation within Perseus of sizes in the range of 1-4 pc. We find that outflows have enough power to maintain the turbulence in these regions and enough momentum to disperse and unbind some mass from them. We found no correlation between outflow strength and star formation efficiency (SFE) for the six different regions we studied, contrary to results of recent numerical simulations. The low fraction of gas that potentially could be ejected due to outflows suggests that additional mechanisms other than cloud dispersal by outflows are needed to explain low SFEs in clusters.

Multiple viewpoint rendering

This paper presents an algorithm for rendering a static scene from multiple perspectives. While most current computer graphics algorithms render scenes as they appear from a single viewpoint (the location of the camera) multiple viewpoint rendering (MVR) renders a scene from a range of spatially-varying viewpoints. By exploiting perspective coherence, MVR can produce a set of images orders of magnitude faster than conventional rendering methods. Images produced by MVR can be used as input to multiple-perspective displays such as holographic stereograms, lenticular sheet displays, and holographic video. MVR can also be used as a geometry-to-image prefilter for image-based rendering algorithms. MVR techniques are adapted from single viewpoint computer graphics algorithms and can be accelerated using existing hardware graphics subsystems. This paper describes the characteristics of MVR algorithms in general, along with the design, implementation, and applications of a particular MVR rendering system.

Holographic stereograms as discrete imaging systems

Unlike holograms of real objects, holographic stereograms consist of information recorded from a relatively small number of discrete viewpoints. As discrete imaging systems, holographic stereograms are susceptible to aliasing artifacts caused by insufficient or improper sampling. A characterization of sampling-related image artifacts in holographic stereograms is presented. Constraints on image extent and resolution imposed by sampling are outlined. Methods of reducing or eliminating aliasing artifacts in both photographically-recorded and computer-generated holographic stereogram images are described. Results of this analysis can be generalized to describe other autostereoscopic displays.

Reconfigurable image projection holograms

We introduce reconfigurable image projection RIP holo- grams and a method for computing RIP holograms of three-dimensional 3-D scenes. RIP holograms project one or more series of parallax views of a 3-D scene through one or more holographically reconstructed projection surfaces. Projection surfaces are defined at locations at which the hologram reconstructs a variable number of real or virtual images, called holographic primitives, which collectively compose the surface and constitute exit pupils for the view pixel information. RIP holograms are efficiently assembled by combining a sweep of 2-D parallax views of a scene with instances of one or more precomputed diffractive elements, which are permitted to overlap on the hologram, and which reconstruct the holographic primitives. The technique improves on the image quality of conventional stereograms while affording similar efficient computation: it incorporates realistic computer graphic rendering or high-quality optical capture of a scene, it eliminates some artifacts often present in conven- tional computed stereograms, and its basic multiply-and-accumulate op- erations are suitable for hardware implementation. The RIP approach offers flexible tuning of capture and projection together, according to the sampling requirements of the scene and the constraints of a given dis- play architecture.

LightKit: a lighting system for effective visualization

LightKit is a system for lighting three-dimensional synthetic scenes. LightKit simplifies the task of producing visually pleasing, easily interpretable images for visualization while making it harder to produce results where the scene illumination distracts from the visualization process. LightKit is based on lighting designs developed by artists and photographers and shown in previous studies to enhance shape perception. A key light provides natural overhead illumination of the scene, augmented by fill, head, and back lights. By default, lights are attached to a normalized, subject-centric, camera-relative coordinate frame to ensure consistent lighting independent of camera location or orientation. This system allows all lights to be positioned by specifying just six parameters. The intensity of each light is specified as a ratio to the key light intensity, allowing the scenes brightness to be adjusted using a single parameter. The color of each light is specified by a single normalized color parameter called warmth that is based on color temperature of natural sources. LightKits default values for light position, intensity, and color are chosen to produce good results for a variety of scenes. LightKit is designed to work with both hardware graphics systems and, potentially, higher quality off-line rendering systems. We provide examples of images created using a LightKit implementation within the VTK visualization toolkit software framework.

Compact prototype one-step Ultragram printer

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.

Interactive visualization and manipulation of 3-D reconstructions for the planning of surgical procedures

The requirements for 3-D reconstructions to be useful in a clinical environment include availability of the imaging and computing hardware; sophisticated and user-friendly software that can be used by physicians or technicians; robust data that can be efficiently segmented into clinically relevant structures; interactive speed; and the ability to manipulate the visualized structures for the simulation of surgical procedures. We have developed an efficient hardware, software, and application environment that fulfills these requirements and have initiated testing of its performance.

3D Morphometric and Morphologic Information Derived From Clinical Brain MR Images

Data from conventional clinical MR brain images were processed using multi-step computerized segmentation as well as 3D analysis and rendering techniques. The usefulness of so obtained morphometric information and morphologic display for the development of new concepts for diagnosis and follow up of diseases was demonstrated with data sets from patients with Alzheimer’s disease, normal pressure hydrocephalus, multiple sclerosis and brain tumors.