Abstract: Appearance reproduction is an important aspect of 3D printing. Current color reproduction systems use halftoning methods that create colors through a spatial combination of different inks at the object's surface. This introduces a variety of artifacts to the object, especially when viewed from a closer distance.

In this work, we propose an alternative color reproduction method for 3D printing. Inspired by the inherent ability of 3D printers to layer different materials on top of each other, 3D color contoning creates colors by combining inks with various thicknesses inside the object's volume.

Since inks are inside the volume, our technique results in a uniform color surface with virtually invisible spatial patterns on the surface. For color prediction, we introduce a simple and highly accurate spectral model that relies on a weighted regression of spectral absorptions. We fully characterize the proposed framework by addressing a number of problems, such as material arrangement, calculation of ink concentration, and 3D dot gain. We use a custom 3D printer to fabricate and validate our results.

Abstract: We demonstrate a new approach for designing functional material definitions for multi-material fabrication using our system called Foundry.

Foundry provides an interactive and visual process for hierarchically designing spatially-varying material properties (e.g., appearance, mechanical, optical). The resulting meta-materials exhibit structure at the micro and macro level and can surpass the qualities of traditional composites. The material definitions are created by composing a set of operators into an operator graph.

Each operator performs a volume decomposition operation, remaps space, or constructs and assigns a material composition. The operators are implemented using a domain-specific language for multi-material fabrication; users can easily extend the library by writing their own operators. Foundry can be used to build operator graphs that describe complex, parameterized, resolution-independent, and reusable material definitions.

We also describe how to stage the evaluation of the final material definition which in conjunction with progressive refinement, allows for interactive material evaluation even for complex designs. We show sophisticated and functional parts designed with our system.

Abstract: 3D printing hardware is rapidly scaling up to output continuous mixtures of multiple materials at increasing resolution over ever larger print volumes. This poses an enormous computational challenge: large high-resolution prints comprise trillions of voxels and petabytes of data and simply modeling and describing the input with spatially varying material mixtures at this scale is challenging. Existing 3D printing software is insufficient; in particular, most software is designed to support only a few million primitives, with discrete material choices per object.

We present OpenFab, a programmable pipeline for synthesis of multi-material 3D printed objects that is inspired by RenderMan and modern GPU pipelines. The pipeline supports procedural evaluation of geometric detail and material composition, using shader-like fablets, allowing models to be specified easily and efficiently. We describe a streaming architecture for OpenFab; only a small fraction of the final volume is stored in memory and output is fed to the printer with little startup delay. We demonstrate it on a variety of multi-material objects.

Abstract: We present surface based anti-aliasing (SBAA), a new approach to real-time anti-aliasing for deferred renderers that improves the performance and lowers the memory requirements for anti-aliasing methods that sample sub-pixel visibility. We introduce a novel way of decoupling visibility determination from shading that, compared to previous multi-sampling based approaches, significantly reduces the number of samples stored and shaded per pixel. Unlike post-process anti-aliasing techniques used in conjunction with deferred renderers, SBAA correctly resolves visibility of sub-pixel features, minimizing spatial and temporal artifacts.

Abstract: We introduce adaptive volumetric shadow maps (AVSM), a real-time shadow algorithm that supports high-quality shadowing from dynamic volumetric media such as hair and smoke. The key contribution of AVSM is the introduction of a streaming simplification algorithm that generates an accurate volumetric light attenuation function using a small fixed memory footprint. This compression strategy leads to high performance because the visibility data can remain in on-chip memory during simplification and can be efficiently sampled during rendering. We demonstrate that AVSM compression closely approximates the ground-truth correct solution and performs competitively to existing real-time rendering techniques while providing higher quality volumetric shadows.

Abstract: In computer cinematography, the process of lighting design involves placing and configuring lights to define the visual appearance of environments and to enhance story elements. This process is labor intensive and time consuming, primarily because lighting artists receive poor feedback from existing tools: interactive previews have very poor quality, while final-quality images often take hours to render.

This paper presents an interactive cinematic lighting system used in the production of computer-animated feature films containing environments of very high complexity, in which surface and light appearances are described using procedural RenderMan shaders. Our system provides lighting artists with high-quality previews at interactive framerates with only small approximations compared to the final rendered images. This is accomplished by combining numerical estimation of surface response, image-space caching, deferred shading, and the computational power of modern graphics hardware.

Our system has been successfully used in the production of two feature-length animated films, dramatically accelerating lighting tasks. In our experience interactivity fundamentally changes an artist's workflow, improving both productivity and artistic expressiveness.

Abstract: In this chapter, we present a simplified implementation of uberlight, a light shader that expresses the lighting model described by Ronen Barzel (1997, 1999). A superset of this model was developed over several years at Pixar Animation Studios and used for the production of animated movies such as the Walt Disney presentations of the Pixar Animation Studios films Toy Story, A Bug's Life, Monsters, Inc., and Finding Nemo. Our Cg implementation is based on Barzel's original approach and on the RenderMan Shading Language implementation written by Larry Gritz (Barzel 1999). Further details about this lighting approach and its uses in movie production can be found in Apodaca and Gritz 1999 and Birn 2000.

Abstract: Real-time graphics hardware continues to offer improved resources for programmable vertex and fragment shaders. However, shader programmers continue to write shaders that require more resources than are available in the hardware. One way to virtualize the resources necessary to run complex shaders is to partition the shaders into multiple rendering passes. This problem, called the "Multi-Pass Partitioning Problem" (MPP), and a solution for the problem, Recursive Dominator Split (RDS), have been presented by Eric Chan et al. The O(n3) RDS algorithm and its heuristic-based O(n2) cousin, RDSh, are robust in that they can efficiently partition shaders for many architectures with varying resources. However, RDS's high runtime cost and inability to handle multiple outputs per pass make it less desirable for real-time use on today's latest graphics hardware. This paper redefines the MPP as a scheduling problem and uses scheduling algorithms that allow incremental resource estimation and pass computation in O(n log n) time. Our scheduling algorithm, Mio, is experimentally compared to RDS and shown to have better run-time scaling and produce comparable partitions for emerging hardware architectures.

Abstract: Normal meshes are new fundamental surface descriptions inspired by differential geometry. A normal mesh is a multiresolution mesh where each level can be written as a normal offset from a coarser version. Hence the mesh can be stored with a single float per vertex. We present an algorithm to approximate any surface arbitrarily closely with a normal semi-regular mesh. Normal meshes can be useful in numerous applications such as compression, filtering, rendering, texturing, and modeling.

Abstract: We describe a 3D graphical interaction tool called an amplification widget that allows a user to control the position or orientation of an object at multiple scales. Fine and coarse adjustments are available within a single tool which gives visual feedback to indicate the level of resolution being applied. Amplification widgets have been included in instructional modules of The Optics Project, designed to supplement undergraduate physics courses. The user evaluation is being developed by the Institute of the Mid-South Educational Research Association under the sponsorship of a 2-year grant from the National Science Foundation.

Abstract: The Optics Project (TOP) is a 3D interactive computer graphics system that visualizes optical phenomena. The primary motivation for creating TOP was to develop an educational aide for the student studying undergraduate optics. TOP runs on SGI workstations and PC computers. We have developed a Web-based version of the system that encompasses a physical simulation, an overview of the theory involved, a showcase of examples, and a set of suggested exercises. The actual simulation is implemented using VRML, Java, and the External Authoring Interface. This work is significant in that it represents, to our knowledge, the first complete 3D interactive optics system on the Web.

Abstract: This paper describes the representation and navigation of large, multi-resolution, georeferenced datasets in VRML97. This requires resolving nontrivial issues such as how to represent deep level of detail hierarchies efficiently in VRML; how to model terrain using geographic coordinate systems instead of only VRML’s Cartesian representation; how to model georeferenced coordinates to sub-meter accuracy with only single-precision floating point support; how to enable the integration of multiple terrain datasets for a region, as well as cultural features such as buildings and roads; how to navigate efficiently around a large, global terrain dataset; and finally, how to encode metadata describing the terrain. We present solutions to all of these problems. Consequently, we are able to visualize geographic data in the order of terabytes or more, from the globe down to millimeter resolution, and in real-time, using standard VRML97.

Abstract: We describe how a Web-based visualization tool can be constructed using Java and VRML, and present a brief survey of the choices available for providing (a) 3D graphics and (b) behavior in a Web browser. The tool is collaborative, multi-platform, and interactive. Through this tool a user can interactively modify and view a physical simulation and share the changes dynamically with other users. The design described has been implemented and successfully run through Netscape and Internet Explorer on Unix workstations and Windows PCs.

Abstract: We describe a multidisciplinary effort for creating interactive 3D graphical modules for visualizing optical phenomena. These mod- ules are designed for use in an upper-level undergraduate course. The modules are developed in Open Inventor, which allows them to run under both Unix and Windows. The work is significant in that it applies contemporary interactive 3D visualization techniques to instructional courseware, which represents a considerable advance compared to the current state of the practice.