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Item A Data-Driven Approach to Realistic Shape Morphing(The Eurographics Association and Blackwell Publishing Ltd., 2013) Gao, Lin; Lai, Yu-Kun; Huang, Qi-Xing; Hu, Shi-Min; I. Navazo, P. PoulinMorphing between 3D objects is a fundamental technique in computer graphics. Traditional methods of shape morphing focus on establishing meaningful correspondences and finding smooth interpolation between shapes. Such methods however only take geometric information as input and thus cannot in general avoid producing unnatural interpolation, in particular for large-scale deformations. This paper proposes a novel data-driven approach for shape morphing. Given a database with various models belonging to the same category, we treat them as data samples in the plausible deformation space. These models are then clustered to form local shape spaces of plausible deformations. We use a simple metric to reasonably represent the closeness between pairs of models. Given source and target models, the morphing problem is casted as a global optimization problem of finding a minimal distance path within the local shape spaces connecting these models. Under the guidance of intermediate models in the path, an extended as-rigid-as-possible interpolation is used to produce the final morphing. By exploiting the knowledge of plausible models, our approach produces realistic morphing for challenging cases as demonstrated by various examples in the paper.Item A Rigging-Skinning Scheme to Control Fluid Simulation(The Eurographics Association and John Wiley & Sons Ltd., 2019) Lu, Jia-Ming; Chen, Xiao-Song; Yan, Xiao; Li, Chen-Feng; Lin, Ming; Hu, Shi-Min; Lee, Jehee and Theobalt, Christian and Wetzstein, GordonInspired by skeletal animation, a novel rigging-skinning flow control scheme is proposed to animate fluids intuitively and efficiently. The new animation pipeline creates fluid animation via two steps: fluid rigging and fluid skinning. The fluid rig is defined by a point cloud with rigid-body movement and incompressible deformation, whose time series can be intuitively specified by a rigid body motion and a constrained free-form deformation, respectively. The fluid skin generates plausible fluid flows by virtually fluidizing the point-cloud fluid rig with adjustable zero- and first-order flow features and at fixed computational cost. Fluid rigging allows the animator to conveniently specify the desired low-frequency flow motion through intuitive manipulations of a point cloud, while fluid skinning truthfully and efficiently converts the motion specified on the fluid rig into plausible flows of the animation fluid, with adjustable fine-scale effects. Besides being intuitive, the rigging-skinning scheme for fluid animation is robust and highly efficient, avoiding completely iterative trials or time-consuming nonlinear optimization. It is also versatile, supporting both particle- and grid- based fluid solvers. A series of examples including liquid, gas and mixed scenes are presented to demonstrate the performance of the new animation pipeline.Item Learning Explicit Smoothing Kernels for Joint Image Filtering(The Eurographics Association and John Wiley & Sons Ltd., 2019) Fang, Xiaonan; Wang, Miao; Shamir, Ariel; Hu, Shi-Min; Lee, Jehee and Theobalt, Christian and Wetzstein, GordonSmoothing noises while preserving strong edges in images is an important problem in image processing. Image smoothing filters can be either explicit (based on local weighted average) or implicit (based on global optimization). Implicit methods are usually time-consuming and cannot be applied to joint image filtering tasks, i.e., leveraging the structural information of a guidance image to filter a target image.Previous deep learning based image smoothing filters are all implicit and unavailable for joint filtering. In this paper, we propose to learn explicit guidance feature maps as well as offset maps from the guidance image and smoothing parameter that can be utilized to smooth the input itself or to filter images in other target domains. We design a deep convolutional neural network consisting of a fully-convolution block for guidance and offset maps extraction together with a stacked spatially varying deformable convolution block for joint image filtering. Our models can approximate several representative image smoothing filters with high accuracy comparable to state-of-the-art methods, and serve as general tools for other joint image filtering tasks, such as color interpolation, depth map upsampling, saliency map upsampling, flash/non-flash image denoising and RGB/NIR image denoising.Item Interactive Image-Guided Modeling of Extruded Shapes(The Eurographics Association and John Wiley and Sons Ltd., 2014) Cao, Yan-Pei; Ju, Tao; Fu, Zhao; Hu, Shi-Min; J. Keyser, Y. J. Kim, and P. WonkaA recent trend in interactive modeling of 3D shapes from a single image is designing minimal interfaces, and accompanying algorithms, for modeling a specific class of objects. Expanding upon the range of shapes that existing minimal interfaces can model, we present an interactive image-guided tool for modeling shapes made up of extruded parts. An extruded part is represented by extruding a closed planar curve, called base, in the direction orthogonal to the base. To model each extruded part, the user only needs to sketch the projected base shape in the image. The main technical contribution is a novel optimization-based approach for recovering the 3D normal of the base of an extruded object by exploring both geometric regularity of the sketched curve and image contents. We developed a convenient interface for modeling multi-part shapes and a method for optimizing the relative placement of the parts. Our tool is validated using synthetic data and tested on real-world images.Item Shrinkability Maps for Content-Aware Video Resizing(The Eurographics Association and Blackwell Publishing Ltd, 2008) Zhang, Yi-Fei; Hu, Shi-Min; Martin, Ralph R.A novel method is given for content-aware video resizing, i.e. targeting video to a new resolution (which may involve aspect ratio change) from the original.We precompute a per-pixel cumulative shrinkability map which takes into account both the importance of each pixel and the need for continuity in the resized result. (If both x and y resizing are required, two separate shrinkability maps are used, otherwise one suffices). A random walk model is used for efficient offline computation of the shrinkability maps. The latter are stored with the video to create a multi-sized video, which permits arbitrary-sized new versions of the video to be later very efficiently created in real-time, e.g. by a video-on-demand server supplying video streams to multiple devices with different resolutions. These shrinkability maps are highly compressible, so the resulting multi-sized videos are typically less than three times the size of the original compressed video. A scaling function operates on the multi-sized video, to give the new pixel locations in the result, giving a high-quality content-aware resized video.Despite the great efficiency and low storage requirements for our method, we produce results of comparable quality to state-of-the-art methods for content-aware image and video resizing.Item Data-Driven Object Manipulation in Images(The Eurographics Association and John Wiley and Sons Ltd., 2012) Goldberg, Chen; Chen, Tao; Zhang, Fang-Lue; Shamir, Ariel; Hu, Shi-Min; P. Cignoni and T. ErtlWe present a framework for interactively manipulating objects in a photograph using related objects obtained from internet images. Given an image, the user selects an object to modify, and provides keywords to describe it. Objects with a similar shape are retrieved and segmented from online images matching the keywords, and deformed to correspond with the selected object. By matching the candidate object and adjusting manipulation parameters, our method appropriately modifies candidate objects and composites them into the scene. Supported manipulations include transferring texture, color and shape from the matched object to the target in a seamless manner. We demonstrate the versatility of our framework using several inputs of varying complexity, for object completion, augmentation, replacement and revealing. Our results are evaluated using a user study.Item Real-time homogenous translucent material editing(The Eurographics Association and Blackwell Publishing Ltd, 2007) Xu, Kun; Gao, Yue; Li, Yong; Ju, Tao; Hu, Shi-MinThis paper presents a novel method for real-time homogenous translucent material editing under fixed illumination. We consider the complete analytic BSSRDF model proposed by Jensen et al. [JMLH01], including both multiple scattering and single scattering. Our method allows the user to adjust the analytic parameters of BSSRDF and provides high-quality, real-time rendering feedback. Inspired by recently developed Precomputed Radiance Transfer (PRT) techniques, we approximate both the multiple scattering diffuse reflectance function and the single scattering exponential attenuation function in the analytic model using basis functions, so that re-computing the outgoing radiance at each vertex as parameters change reduces to simple dot products. In addition, using a non-uniform piecewise polynomial basis, we are able to achieve smaller approximation error than using bases adopted in previous PRT-based works, such as spherical harmonics and wavelets. Using hardware acceleration, we demonstrate that our system generates images comparable to [JMLH01]at real-time frame-rates.Item Saliency-aware Real-time Volumetric Fusion for Object Reconstruction(The Eurographics Association and John Wiley & Sons Ltd., 2016) Yang, Sheng; Chen, Kang; Liu, Minghua; Fu, Hongbo; Hu, Shi-Min; Jernej Barbic and Wen-Chieh Lin and Olga Sorkine-HornungWe present a real-time approach for acquiring 3D objects with high fidelity using hand-held consumer-level RGB-D scanning devices. Existing real-time reconstruction methods typically do not take the point of interest into account, and thus might fail to produce clean reconstruction results of desired objects due to distracting objects or backgrounds. In addition, any changes in background during scanning, which can often occur in real scenarios, can easily break up the whole reconstruction process. To address these issues, we incorporate visual saliency into a traditional real-time volumetric fusion pipeline. Salient regions detected from RGB-D frames suggest user-intended objects, and by understanding user intentions our approach can put more emphasis on important targets, and meanwhile, eliminate disturbance of non-important objects. Experimental results on realworld scans demonstrate that our system is capable of effectively acquiring geometric information of salient objects in cluttered real-world scenes, even if the backgrounds are changing.Item Appearance Harmonization for Single Image Shadow Removal(The Eurographics Association and John Wiley & Sons Ltd., 2016) Ma, Li-Qian; Wang, Jue; Shechtman, Eli; Sunkavalli, Kalyan; Hu, Shi-Min; Eitan Grinspun and Bernd Bickel and Yoshinori DobashiShadow removal is a challenging problem and previous approaches often produce de-shadowed regions that are visually inconsistent with the rest of the image. We propose an automatic shadow region harmonization approach that makes the appearance of a de-shadowed region (produced using any previous technique) compatible with the rest of the image. We use a shadow-guided patch-based image synthesis approach that reconstructs the shadow region using patches sampled from nonshadowed regions. This result is then refined based on the reconstruction confidence to handle unique textures. Qualitative comparisons over a wide range of images, and a quantitative evaluation on a benchmark dataset show that our technique significantly improves upon the state-of-the-art.Item A Shape-Preserving Approach to Image Resizing(The Eurographics Association and Blackwell Publishing Ltd, 2009) Zhang, Guo-Xin; Cheng, Ming-Ming; Hu, Shi-Min; Martin, Ralph R.We present a novel image resizing method which attempts to ensure that important local regions undergo a geometric similarity transformation, and at the same time, to preserve image edge structure. To accomplish this, we define handles to describe both local regions and image edges, and assign a weight for each handle based on an importance map for the source image. Inspired by conformal energy, which is widely used in geometry processing, we construct a novel quadratic distortion energy to measure the shape distortion for each handle. The resizing result is obtained by minimizing the weighted sum of the quadratic distortion energies of all handles. Compared to previous methods, our method allows distortion to be diffused better in all directions, and important image edges are well-preserved. The method is efficient, and offers a closed form solution.