Anselmo Lastra

LDI tree: a hierarchical representation for image-based rendering

Using multiple reference images in 3D image warping has been a challenging problem. Recently, the Layered Depth Image (LDI) was proposed by Shade et al. to merge multiple reference images under a single center of projection, while maintaining the simplicity of warping a single reference image. However it does not consider the issue of sampling rate. We present the LDI tree, which combines a hierarchical space partitioning scheme with the concept of the LDI. It preserves the sampling rates of the reference images by adaptively selecting an LDI in the LDI tree for each pixel. While rendering from the LDI tree, we only have to traverse the LDI tree to the levels that are comparable to the sampling rate of the output image. We also present a progressive refinement feature and a “gap filling” algorithm implemented by pre-filtering the LDI tree. We show that the amount of memory required has the same order of growth as the 2D reference images. This also bounds the complexity of rendering time to be less than directly rendering from all reference images. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation Viewing Algorithms; I.3.6 [Computer Graphics] Methodology and Techniques Graphics data structures and data types; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism. Additional

Real-Time Cloud Rendering

This paper presents a method for realistic real‐time rendering of clouds suitable for flight simulation and games. It provides a cloud shading algorithm that approximates multiple forward scattering in a preprocess, and first order anisotropic scattering at runtime. Impostors are used to accelerate cloud rendering by exploiting frame‐to‐frame coherence in an interactive flight simulation. Impostors are shown to be particularly well suited to clouds, even in circumstances under which they cannot be applied to the rendering of polygonal geometry. The method allows hundreds of clouds and hundreds of thousands of particles to be rendered at high frame rates, and improves interaction with clouds by reducing artifacts introduced by direct particle rendering techniques.

Physically-based visual simulation on graphics hardware

In this paper, we present a method for real-time visual simulation of diverse dynamic phenomena using programmable graphics hardware. The simulations we implement use an extension of cellular automata known as the coupled map lattice (CML). CML represents the state of a dynamic system as continuous values on a discrete lattice. In our implementation we store the lattice values in a texture, and use pixel-level programming to implement simple next-state computations on lattice nodes and their neighbors. We apply these computations successively to produce interactive visual simulations of convection, reaction-diffusion, and boiling. We have built an interactive framework for building and experimenting with CML simulations running on graphics hardware, and have integrated them into interactive 3D graphics applications.In this paper, we present a method for real-time visual simulation of diverse dynamic phenomena using programmable graphics hardware. The simulations we implement use an extension of cellular automata known as the coupled map lattice (CML). CML represents the state of a dynamic system as continuous values on a discrete lattice. In our implementation we store the lattice values in a texture, and use pixel-level programming to implement simple next-state computations on lattice nodes and their neighbors. We apply these computations successively to produce interactive visual simulations of convection, reaction-diffusion, and boiling. We have built an interactive framework for building and experimenting with CML simulations running on graphics hardware, and have integrated them into interactive 3D graphics applications.

Fast Summed-Area Table Generation and its Applications

We introduce a technique to rapidly generate summed-area tables using graphics hardware. Summed area tables, originally introduced by Crow, provide a way to filter arbitrarily large rectangular regions of an image in a constant amount of time. Our algorithm for generating summed-area tables, similar to a technique used in scientific computing called recursive doubling, allows the generation of a summed-area table in O(log n) time. We also describe a technique to mitigate the precision requirements of summed-area tables. The ability to calculate and use summed-area tables at interactive rates enables numerous interesting rendering effects. We present several possible applications. First, the use of summed-area tables allows real-time rendering of interactive, glossy environmental reflections. Second, we present glossy planar reflections with varying blurriness dependent on a reflected object’s distance to the reflector. Third, we show a technique that uses a summed-area table to render glossy transparent objects. The final application demonstrates an interactive depth-of-field effect using summedarea tables.

A shading language on graphics hardware: the pixelflow shading system

Over the years, there have been two main branches of computer graphics image-synthesis research; one focused on interactivity, the other on image quality. Procedural shading is a powerful tool, commonly used for creating high-quality images and production animation. A key aspect of most procedural shading is the use of a shading language, which allows a high-level description of the color and shading of each surface. However, shading languages have been beyond the capabilities of the interactive graphics hardware community. We have created a parallel graphics multicomputer, PixelFlow, that can render images at 30 frames per second using a shading language. This is the first system to be able to support a shading language in real-time. In this paper, we describe some of the techniques that make this possible.

PixelFlow: the realization

PlxelFlow is an architecture for high-speed, highly realistic image generation, based on the techniques of object-parallelism and image composition, Its initial architecture was described in [MOLN92]. After development by the original team of researchers at the University of North Carolina, and codevelopment with industry partners, Division Ltd. and HcwlettPackard, PixelFlow now is a much more capable system than initially conceived and its hardware and software systems have evolved considerably. This paper describes the final realization of PixelFlow, along with hardware and software enhancements heretofore unpublished. CR Cntcgorics and Subject Descriptors: C.5.4 [Computer System Implementation]: VLSI Systems; 1.3.1 [Computer Graphics]: Hardware Architecture; 1.3.3 [Computer Graphics]: Picture/Image Generation; 1.3.7 [Computer Graphics]: ThreeDimensional Graphics and Realism. Additlonnl

Life-sized projector-based dioramas

We introduce an idea and some preliminary results for a new projector-based approach to re-creating real and imagined sites. Our goal is to achieve re-creations that are both visually and spatially realistic, providing a small number of relatively unencumbered users with a strong sense of immersion as they jointly walkaround the virtual site.Rather than using head-mounted or general-purpose projector-based displays, our idea builds on previous projector-based work on spatially-augmented realityand shader lamps. Using simple white building blocks we construct a static physical model that approximates the size, shape, and spatial arrangementof the site. We then project dynamic imagery onto the blocks, transforming the lifeless physical model into a visually faithful reproduction of the actual site. Some advantages of this approach include wide field-of-view imagery, real walking around the site, reduced sensitivity to tracking errors, reduced sensitivity to system latency, auto-stereoscopic vision, the natural addition of augmented virtualityand the provision of haptics.In addition to describing the major challenges to (and limitations of) this vision, in this paper we describe some short-term solutions and practical methods, and we present some proof-of-concept results.

Automatic image placement to provide a guaranteed frame rate

We present a preprocessing algorithm and run-time system for rendering 3D geometric models at a guaranteed frame rate. Our approach trades off space for frame rate by using images to replace distant geometry. The preprocessing algorithm automatically chooses a subset of the model to display as an image so as to render no more than a specified number of geometric primitives. We also summarize an optimized layered-depth-image warper to display images surrounded by geometry at run time. Furthermore, we show the results of applying our method to accelerate the interactive walkthrough of several complex models.

Architectural walkthroughs using portal textures

This paper outlines a method to dynamically replace portals with textures in a cell-partitioned model. The rendering complexity is reduced to the geometry of the current cell thus increasing interactive performance. A portal is a generalization of windows and doors. It connects two adjacent cells (or rooms). Each portal of the current cell that is some distance away from the viewpoint is rendered as a texture. The portal texture (smoothly) returns to geometry when the viewpoint gets close to the portal. This way all portal sequences (not too close to the viewpoint) have a depth complexity of one. The size of each texture and distance at which the transition occurs is configurable for each portal.

Real-Time Rendering of Real World Environments

One of the most important goals of interactive computer graphics is to allow a user to freely walk around a virtual recreation of a real environment that looks as real as the world around us. But hand-modeling such a virtual environment is inherently limited and acquiring the scene model using devices also presents challenges. Interactively rendering such a detailed model is beyond the limits of current graphics hardware, but image-based approaches can significantly improve the status quo. We present an end-to-end system for acquiring highly detailed scans of large real world spaces, consisting of forty to eighty million range and color samples, using a digital camera and laser rangefinder. We explain successful techniques to represent these large data sets as image-based models and present contributions to image-based rendering that allow these models to be rendered in real time on existing graphics hardware without sacrificing the high resolution at which the data sets were acquired.