This study presents a safe and easy-to-use gait evaluation framework for low-light environments. We simulate such environments by applying a low-light filter to the passthrough image of a mixed-reality (MR) device. Using this setup, we also introduce an MR-based 5-meter walk test that can place virtual obstacles and record the trajectories of the feet, hands, and head during walking. In the user study, we observed that walking speed and step length tended to increase in the MR-simulated low-light environment, which is consistent with previous reports on real low-light environments.

The goal of this study is to support efficient and consistent three-dimensional (3D) painting in virtual reality (VR) space. For this, we propose the use of deformable primitives as a construction guide in the early stages of 3D painting and introduce FlexiPrim, consisting of two primitive types, cuboid and ellipsoid. The user can deform FlexiPrim by manipulating the control points in VR space. We conducted a user study to compare FlexiPrim with traditional Guide-Objects in OpenBrush, where the latter has an automatic snapping function. As a result, we found that the proposed method enables the creation of construction guides consisting of curved elements, and participants provided positive feedback on the subsequent rough sketch using the FlexiPrim as guide.

This study proposes a method for realizing a spatiotemporal teleportation experience in a real-world environment using mixed reality (MR) technology and an omnidirectional (omni-) camera. In an environment where an omni-camera is placed, the user wears a head-mounted display (HMD) to enter the MR space. This MR space provides a marker at the omni-camera, allowing the user to select it and teleport their viewpoint to the camera. During teleportation, the user can also revisit past scenes by reviewing omni-videos recorded earlier. To illustrate the feasibility of the method, we present three example application scenarios: landscape viewing, sports viewing, and surveillance. The results of our user study suggest that the method is easy for novice users to operate, and participants particularly enjoyed the time-shift function, which allowed them to review past moments.

We present the Mokume dataset for solid wood texturing consisting of 190 cube-shaped samples of various hard and softwood species documented by high-resolution exterior photographs, annual ring annotations, and volumetric computed tomography (CT) scans. A subset of samples further includes photographs along slanted cuts through the cube for validation purposes. Using this dataset, we propose a three-stage inverse modeling pipeline to infer solid wood textures using only exterior photographs. Our method begins by evaluating a neural model to localize year rings on the cube face photographs. We then extend these exterior 2D observations into a globally consistent 3D representation by optimizing a procedural growth field using a novel iso-contour loss. Finally, we synthesize a detailed volumetric color texture from the growth field. For this last step, we propose two methods with different efficiency and quality characteristics: a fast inverse procedural texture method, and a neural cellular automaton (NCA). We demonstrate the synergy between the Mokume dataset and the proposed algorithms through comprehensive comparisons with unseen captured data. We also present experiments demonstrating the efficiency of our pipeline's components against ablations and baselines. Our code, the dataset, and reconstructions are available via https://mokumeproject.github.io/.

Abstract We propose a method for inferring the internal anisotropic volumetric texture of a given wood block from annotated photographs of its external surfaces. The global structure of the annual ring pattern is represented using a continuous spatial scalar field referred to as the growth time field (GTF). First, we train a generic neural model that can represent various GTFs using procedurally generated training data. Next, we fit the generic model to the GTF of a given wood block based on surface annotations. Finally, we convert the GTF to an annual ring field (ARF) revealing the layered pattern and apply neural style transfer to render orientation‐dependent small‐scale features and colors on a cut surface. We show rendered results of various physically cut real wood samples. Our method has physical and virtual applications such as cut‐preview before subtractive fabricating solid wood artifacts and simulating object breaking.

Abstract Ninety‐degree pop‐ups are a type of papercraft on which a three‐dimensional (3D) structure pops up when the angle of the base fold is 90°. They are fabricated by cutting and creasing a single sheet of paper. Traditional 90° pop‐ups are limited to 3D shapes only comprising planar shapes because they are made of paper. In this paper, we present novel pop‐ups, fabricatable 90° pop‐ups that employ the 90° pop‐up mechanism, consist of components with curved shapes, and can be fabricatable using a 3D printer. We propose a method for converting a 3D model into a fabricatable 90° pop‐up. The user first interactively designs a layout of pop‐up components, and the system automatically deforms the components using the 3D model. Because the generated pop‐ups contain necessary cuts and folds, no additional assembly process is required. To demonstrate the feasibility of the proposed method, we designed and fabricated various 90° pop‐ups using a 3D printer.

We present a procedural framework for modeling the annual ring pattern of solid wood with knots. Although wood texturing is a well-studied topic, there have been few previous attempts at modeling knots inside the wood texture. Our method takes the skeletal structure of a tree log as input and produces a three-dimensional scalar field representing the time of added growth, which defines the volumetric annual ring pattern. First, separate fields are computed around each strand of the skeleton, i.e., the stem and each knot. The strands are then merged into a single field using smooth minimums. We further suggest techniques for controlling the smooth minimum to adjust the balance of smoothness and reproduce the distortion effects observed around dead knots. Our method is implemented as a shader program running on a GPU with computation times of approximately 0.5 s per image and an input data size of 600 KB. We present rendered images of solid wood from pine and spruce as well as plywood and cross-laminated timber (CLT). Our results were evaluated by wood experts, who confirmed the plausibility of the rendered annual ring patterns. Link to code: https://github.com/marialarsson/procedural_knots.

The purpose of this study is to develop an easy-to-use ball/strike judgment practice system for inexperienced baseball umpires. The main idea is to provide a practice environment in a Virtual Reality (VR) space. With our system, users observe a pitched ball, perform ball/strike judgment, and review their judgment in a VR space. Since the whole process is completed in VR, users can practice the judgments without preparing a pitcher and catcher. A user investigation in which participants practiced with our system and judged balls thrown by a pitching machine was conducted. The participants responded positively when asked about the usefulness of our system.

In this work, a ray-casting-based three-dimensional (3D) pointing and dragging interface for naked-eye stereoscopic displays is proposed. When a user holds a stylus and points it to a display, the proposed system displays a ray, which extends from the stylus to the virtual space in the display. This ray can be used to interact with objects in the virtual space. By conducting a user study, we found that the proposed method allows users to perform 3D pointing with smaller hand movements compared to a hand-capture-based interface. A model, which extends Fitts’s law, is also proposed. This model is capable of well predicting the time required for a 3D pointing task.

We visualize life-size sequential photographs of sports activities in a mixed reality (MR) environment. Wearing a video-see-through head-mounted display, an observer records the motions of a player using a handheld camera. Our system then places billboards in the three-dimensional MR space, on which the sequential photographs of the player’s motion are presented at life-size. In a user study, we found that the observers perceived the size of the motions more accurately than when viewing sequential photographs on a monitor display.

The compressed sensing using dictionary learning has led to state-of-the-art results for magnetic resonance imaging (MRI) reconstruction from highly under-sampled measurements. Dictionary learning had been considered time-consuming especially when the patch size or the number of training patches is large. Recently, double sparsity model and online dictionary learning algorithm were proposed to obtain dictionaries with much less computational time. In this paper, we propose an efficient MRI reconstruction method by adopting the double sparsity model with the online dictionary learning method. Besides, for better reconstruction, we use separately prepared fully-sampled MRI images to train dictionaries. We compare results of the proposed technique to traditional offline methods with and without double sparsity model. Our simulation results show that the proposed technique is approximately twice faster than the traditional methods while maintaining the same reconstruction quality. Furthermore, our technique performed even better for lower sampling rate.

This paper presents a novel three dimensional (3D) flower modeling technique that utilizes an X-ray computed tomography (CT) system and real-world flowers. Although a CT system provides volume data that captures the internal structures of flowers, it is difficult to accurately segment them into regions of particular organs and model them as smooth surfaces because a flower consists of thin organs that contact one another. We thus introduce a semi-automatic modeling technique that is based on a new active contour model with energy functionals designed for flower CT. Our key idea is to approximate flower components by two important primitives, a shaft and a sheet. Based on our active contour model, we also provide novel user interfaces and a numerical scheme to fit these primitives so as to reconstruct realistic thin flower organs efficiently. To demonstrate the feasibility of our technique, we provide various flower models reconstructed from CT volumes.

Abstract In this paper, we propose a novel contour‐based volume image segmentation technique. Our technique is based on an implicit surface reconstruction strategy, whereby a signed scalar field is generated from user‐specified contours. The key idea is to compute the scalar field in a joint spatial‐range domain (i.e., bilateral domain) and resample its values on an image manifold. We introduce a new formulation of Hermite radial basis function (HRBF) interpolation to obtain the scalar field in the bilateral domain. In contrast to previous implicit methods, bilateral HRBF (B‐HRBF) generates a segmentation boundary that passes through all contours, fits high‐contrast image edges if they exist, and has a smooth shape in blurred areas of images. We also propose an acceleration scheme for computing B‐HRBF to support a real‐time and intuitive segmentation interface. In our experiments, we achieved high‐quality segmentation results for regions of interest with high‐contrast edges and blurred boundaries.

Abstract Medical volume images contain ambiguous and low‐contrast boundaries around which existing fully‐ or semiautomatic segmentation algorithms often cause errors. In this paper, we propose a novel system for intuitively and efficiently refining medical volume segmentation by modifying multiple curved contours. Starting with segmentation data obtained using any existing algorithm, the user places a three‐dimensional curved cross‐section and contours of the foreground region by drawing a cut stroke, and then modifies the contours referring to the cross‐section. The modified contours are used as constraints for deforming a boundary surface that envelops the foreground region, and the region is updated by that deformed boundary. Our surface deformation algorithm seamlessly integrates detail‐preserving and curvature‐diffusing methods to keep important detail boundary features intact while obtaining smooth surfaces around unimportant boundary regions. Our system supports topological manipulations as well as contour shape modifications. We illustrate the feasibility of our system by providing examples of its application to the extraction of bones, muscles, kidneys with blood vessels, and bowels.

Abstract Animations of characters with flexible bodies such as jellyfish, snails, and, hearts are difficult to design using traditional skeleton‐based approaches. A standard approach is keyframing, but adjusting the shape of the flexible body for each key frame is tedious. In addition, the character cannot dynamically adjust its motion to respond to the environment or user input. This paper introduces a new procedural deformation framework (ProcDef) for designing and driving animations of such flexible objects. Our approach is to synthesize global motions procedurally by integrating local deformations. ProcDef provides an efficient design scheme for local deformation patterns; the user can control the orientation and magnitude of local deformations as well as the propagation of deformation signals by specifying line charts and volumetric fields. We also present a fast and robust deformation algorithm based on shape‐matching dynamics and show some example animations to illustrate the feasibility of our framework.

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.

We present a method for representing solid objects with spatially-varying oriented textures by repeatedly pasting solid texture exemplars. The underlying concept is to extend the 2D texture patch-pasting approach of lapped textures to 3D solids using a tetrahedral mesh and 3D texture patches. The system places texture patches according to the user-defined volumetric tensor fields over the mesh to represent oriented textures. We have also extended the original technique to handle nonhomogeneous textures for creating solid models whose textural patterns change gradually along the depth fields. We identify several texture types considering the amount of anisotropy and spatial variation and provide a tailored user interface for each. With our simple framework, large-scale realistic solid models can be created easily with little memory and computational cost. We demonstrate the effectiveness of our approach with several examples including trees, fruits, and vegetables.

Abstract We present an interactive modeling system for flower composition that supports seamless transformation from an initial sketch to a detailed three‐dimensional (3D) model. To begin, the user quickly sketches the overall appearance of the desired model as a collection of two‐dimensional (2D) strokes on hierarchical billboards. Then the user iteratively replaces the coarse sketch with a detailed 3D model referring to the initial sketch as a guide. Since a flower model consists of many repetitive components, the system helps the user to reuse 3D components to facilitate the modeling process. The global view of the entire model is always shown in a separate window to visualize how local modifications affect the global appearance. Our system helps the user make appropriate design decisions to keep the model consistent with the initial design, which is difficult in traditional bottom‐up plant modeling systems in which the global view only emerges after all of the details are specified. Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Computer Graphics]: Methodology and Techniques – Interaction Techniques.

We present a system for modeling flowers in three dimensions quickly and easily while preserving correct botanical structures. We use floral diagrams and inflorescences , which were developed by botanists to concisely describe structural information of flowers. Floral diagrams represent the layout of floral components on a single flower, while inflorescences are arrangements of multiple flowers. Based on these notions, we created a simple user interface that is specially tailored to flower editing, while retaining a maximum variety of generable models. We also provide sketching interfaces to define the geometries of floral components. Separation of structural editing and editing of geometry makes the authoring process more flexible and efficient. We found that even novice users could easily design various flower models using our technique. Our system is an example of application-customized sketching, illustrating the potential power of a sketching interface that is carefully designed for a specific application.