Precisely understanding how objects move in 3D is essential for broad scenarios such as video editing, gaming, driving, and athletics. With screen-displayed computer graphics content, users only perceive limited cues to judge the object motion from the on-screen optical flow. Conventionally, visual perception is studied with stationary settings and singular objects. However, in practical applications, we---the observer---also move within complex scenes. Therefore, we must extract object motion from a combined optical flow displayed on screen, which can often lead to mis-estimations due to perceptual ambiguities. We measure and model observers' perceptual accuracy of object motions in dynamic 3D environments, a universal but under-investigated scenario in computer graphics applications. We design and employ a crowdsourcing-based psychophysical study, quantifying the relationships among patterns of scene dynamics and content, and the resulting perceptual judgments of object motion direction. The acquired psychophysical data underpins a model for generalized conditions. We then demonstrate the model's guidance ability to significantly enhance users' understanding of task object motion in gaming and animation design. With applications in measuring and compensating for object motion errors in video and rendering, we hope the research establishes a new frontier for understanding and mitigating perceptual errors caused by the gap between screen-displayed graphics and the physical world.

Motion-to-photon latency causes images to sway from side to side in a VR/AR system, while display persistence causes smearing; both of these are undesirable artifacts. We show that once latency is reduced or eliminated, smearing due to display persistence becomes the dominant visual artifact, even with accurate tracker prediction. We investigate the human perceptual mechanisms responsible for this and we demonstrate a modified 3D rotation display controller architecture for driving a high speed digital display which minimizes latency and persistence. We simulate it in software and we built a testbench based on a very high frame rate (2880 fps 1-bit images) display system mounted on a mechanical rotation gantry which emulates display rotation during head rotation in an HMD.

When creating a photo album of an event, people typically select a few important images to keep or share. There is some consistency in the process of choosing the important images, and discarding the unimportant ones. Modeling this selection process will assist automatic photo selection and album summarization. In this paper, we show that the selection of important images is consistent among different viewers, and that this selection process is related to the event type of the album. We introduce the concept of event-specific image importance. We collected a new event album dataset with human annotation of the relative image importance with each event album. We also propose a Convolutional Neural Network (CNN) based method to predict the image importance score of a given event album, using a novel rank loss function and a progressive training scheme. Results demonstrate that our method significantly outperforms various baseline methods.

Abstract In this work we detail a method that leverages the two color heads of recent low‐end fused deposition modeling (FDM) 3D printers to produce continuous tone imagery. The challenge behind producing such two‐tone imagery is how to finely interleave the two colors while minimizing the switching between print heads, making each color printed span as long and continuous as possible to avoid artifacts associated with printing short segments. The key insight behind our work is that by applying small geometric offsets, tone can be varied without the need to switch color print heads within a single layer. We can now effectively print (two‐tone) texture mapped models capturing both geometric and color information in our output 3D prints.

Abstract We propose an optimization framework for 3D printing that seeks to save printing time and the support material required to print 3D shapes. Three‐dimensional printing technology is rapidly maturing and may revolutionize how we manufacture objects. The total cost of printing, however, is governed by numerous factors which include not only the price of the printer but also the amount of material and time to fabricate the shape. Our PackMerger framework converts the input 3D watertight mesh into a shell by hollowing its inner parts. The shell is then divided into segments. The location of splits is controlled based on several parameters, including the size of the connection areas or volume of each segment. The pieces are then tightly packed using optimization. The optimization attempts to minimize the amount of support material and the bounding box volume of the packed segments while keeping the number of segments minimal. The final packed configuration can be printed with substantial time and material savings, while also allowing printing of objects that would not fit into the printer volume. We have tested our system on three different printers and it shows a reduction of 5–30% of the printing time while simultaneously saving 15–65% of the support material. The optimization time was approximately 1 min. Once the segments are printed, they need to be assembled.

Abstract Procedural methods present one of the most powerful techniques for authoring a vast variety of computer graphics models. However, their massive applicability is hindered by the lack of control and a low predictability of the results. In the classical procedural modeling pipeline, the user usually defines a set of rules, executes the procedural system, and by examining the results attempts to infer what should be changed in the system definition in order to achieve the desired output. We present guided procedural modeling, a new approach that allows a high level of top‐down control by breaking the system into smaller building blocks that communicate. In our work we generalize the concept of the environment. The user creates a set of guides. Each guide defines a region in which a specific procedural model operates. These guides are connected by a set of links that serve for message passing between the procedural models attached to each guide. The entire model consists of a set of guides with procedural models, a graph representing their connection, and the method in which the guides interact. The modeling process is performed by modifying each of the described elements. The user can control the high‐level description by editing the guides or manipulate the low‐level description by changing the procedural rules. Changing the connectivity allows the user to create new complex forms in an easy and intuitive way. We show several examples of procedural structures, including an ornamental pattern, a street layout, a bridge, and a model of trees. We also demonstrate interactive examples for quick and intuitive editing using physics‐based mass‐spring system.

Abstract We present a method for synthesizing two dimensional (2D) element arrangements from an example. The main idea is to combine texture synthesis techniques based‐on a local neighborhood comparison and procedural modeling systems based‐on local growth. Given a user‐specified reference pattern, our system analyzes neigh‐borhood information of each element by constructing connectivity. Our synthesis process starts with a single seed and progressively places elements one by one by searching a reference element which has local features that are the most similar to the target place of the synthesized pattern. To support creative design activities, we introduce three types of interaction for controlling global features of the resulting pattern, namely a spray tool, a flow field tool, and a boundary tool. We also introduce a global optimization process that helps to avoid local error concentrations. We illustrate the feasibility of our method by creating several types of 2D patterns.

This paper describes the design and implementation of an architecture for interactively viewing static light fields with very low latency. The system was deliberately over engineered to specifications much tighter than expected necessary to eliminate perceptible latency. This allowed us to relax the specifications to the point at which human users began to detect latency artifacts. We found empirically that when interacting with a light field, human users began to notice latency artifacts when the total system latency is approximately 15 ms. Although the architecture may not be used in practice, this result should prove fundamental for designers of future interactive graphics systems. CR Categories and Subject Descriptors: I.3.3 [Computer Graphics]: Picture/Image Generation - Viewing Algorithms. 1

This paper explores some design possibilities and constraints for 3D enhancements of graphical user interfaces (GUIs). This is done with the aim of conveying more information in less screen space, while avoiding visual clutter. Design elements include the use of ‘slapped-back’ windows obtained by projecting windows and icons into three dimensions; ‘trays’, an alternative to folders or piles; the use of transparent ‘beams’ for indicating hierarchy; and the use of ‘periphs’ for a form of fisheye projection on window borders. In addition we employ shading and shadows to enhance the interface, and automatic placement algorithms to prevent visually confusing occlusion. By considering these approaches together, rather than in isolation, the interactions between the different modifications are made explicit. Copyright © 1999 John Wiley & Sons, Ltd.

This paper describes efficient algorithms for the placement and distortion of textures. The textures include surface color maps and environment maps. Affine transformations of a texture, as well as localized warps, are used to align features in the texture with features of the model. Image-space caches are used to enable texture placement in real time.

This paper discusses the use of two different approaches for computing the “accessibility” of a surface. These metrics characterize how easily a surface may be touched by a spherical probe. The paper also presents various acceleration techniques for accessibility. The idea of surface accessibility is extended to include “global accessibility” which measures the ability of a spherical probe to enter a structure from outside as well as to fit locally on the surface. The visual effect of shading using accessibility is shown to resemble the patina on certain tarnished surfaces which have then been cleaned.

An ideal visibility algorithm should a) quickly reject most of the hidden geometry in a model and b) exploit the spatial and perhaps temporal coherence of the images being generated. Ray casting with spatial subdivision does well on criterion (a), but poorly on criterion (b). Traditional Z-buffer scan conversion does well on criterion (b), but poorly on criterion (a). Here we present a hierarchical Z-buffer scan-conversion algorithm that does well on both criteria. The method uses two hierarchical data structures, an object-space octree and an image-space Z pyramid, to accelerate scan conversion. The two hierarchical data structures make it possible to reject hidden geometry very rapidly while rendering visible geometry with the speed of scan conversion. For animation, the algorithm is also able to exploit temporal coherence. The method is well suited to models with high depth complexity, achieving orders of magnitude acceleration in some cases compared to ordinary Z-buffer scan conversion.

Abstract The Virtual Museum is an interactive, electronic museum where users can move from room to room, and select any exhibit in a room for more detailed examination. The exhibits in the museum are educational, encompassing topics such as medicine, plant growth, the environment, and space. To facilitate interaction with the museum, a new method for navigating through a prerendered 3D space, and interacting with objects in that space has been developed, called ‘virtual navigation’. Virtual navigation employs real‐time video decompression for the display of, and interaction with, high‐quality computer animation. In addition, a representation for 3D objects in animated sequences is used which permits pixel‐accurate, frame‐accurate object picking, so that a viewer can select any 3D object to trigger movement within the 3D space, to examine an exhibit in animated form, or to play a digital movie or soundtrack. The use of precomputed video permits 3D navigation in a realistic‐looking space, without requiring special‐purpose graphics hardware.

A new progressive global illumination method is presented which produces approximate images quickly, and then continues to systematically produce more accurate images. The method combines the existing methods of progressive refinement radiosity, Monte Carlo path tracing and light ray tracing. The method does not place any limitation on surface properties such as ideal Lambertian or mirror-like. To increase efficiency and accuracy, the new concepts of light source reclassification, caustics reconstruction, Monte Carlo path tracing with a radiosity preprocess and an interruptible radiosity solution are introduced. The method presents the user with most useful information about the scene as early as possible by reorganizing the method into a radiosity pass, a high frequency refinement pass and a low frequency refinement pass. The implementation of the method is demonstrated, and sample images are presented.

We present a new method for animating water based on a simple, rapid and stable solution of a set of partial differential equations resulting from an approximation to the shallow water equations. The approximation gives rise to a version of the wave equation on a height-field where the wave velocity is proportional to the square root of the depth of the water. The resulting wave equation is then solved with an alternating-direction implicit method on a uniform finite-difference grid. The computational work required for an iteration consists mainly of solving a simple tridiagonal linear system for each row and column of the height field. A single iteration per frame suffices in most cases for convincing animation.Like previous computer-graphics models of wave motion, the new method can generate the effects of wave refraction with depth. Unlike previous models, it also handles wave reflections, net transport of water and boundary conditions with changing topology. As a consequence, the model is suitable for animating phenomena such as flowing rivers, raindrops hitting surfaces and waves in a fish tank as well as the classic phenomenon of waves lapping on a beach. The height-field representation prevents it from easily simulating phenomena such as breaking waves, except perhaps in combination with particle-based fluid models. The water is rendered using a form of caustic shading which simulates the refraction of illuminating rays at the water surface. A wetness map is also used to compute the wetting and drying of sand as the water passes over it.

This paper examines three methods, two existing and one new, for the generation of fractals based on recursive subdivision. Both existing methods are found to have defects, which are not present in the new method. A parallel processing algorithm is proposed for the rendering of height fields which is exact and distributes the load evenly between the processors. A method is described for the 'fan-tracing' of height fields to allow the realistic simulation of water reflections.