Shi-min Hu | Tsinghua University (original) (raw)

Papers by Shi-min Hu

Lecture Notes in Computer Science, 2005

This paper presents a marching method for computing intersection curves between two solids repres... more This paper presents a marching method for computing intersection curves between two solids represented by subdivision surfaces of Catmull-Clark or Loop type. It can be used in trimming and boolean operations for subdivision surfaces. The main idea is to apply a marching method with geometric interpretation to trace the intersection curves. We first determine all intersecting regions, then find pairs of initial intersection points, and trace the intersection curves from the initial intersection points. Various examples are given to demonstrate the robustness and efficiency of our algorithm.

Proceedings Ninth Pacific Conference on Computer Graphics and Applications. Pacific Graphics 2001, 2001

Proceedings the Eighth Pacific Conference on Computer Graphics and Applications, 2000

In this paper we present a matrix-based technique f o r reconstructing solids with quadric suYfac... more In this paper we present a matrix-based technique f o r reconstructing solids with quadric suYface from three orthographic views. First, the relationship between a conic and its orthographic projections is developed using matrix theory. We then address the problem of finding the theoretical minimum number of views that are necessary for reconstructing an object with quadric surjaces. Next, we reconstruct the conic edges by finding their matrix representations in space. This eflectively constructs a wire-fiame model corresponding to the three orthographic views. Finally, volume information is searched within the wire-jrame model to form the final solids. The novelty of'otir algorithm is in the use o f t h e matrix representation of' conics to assist in the 3 0 reconstruction, which increases both the effiiency and the reliability ofthe proposed approach.

Proceedings of the 2006 ACM symposium on Solid and physical modeling - SPM '06, 2006

Segmenting meshes into natural regions is useful for model understanding and many practical appli... more Segmenting meshes into natural regions is useful for model understanding and many practical applications. In this paper, we present a novel, automatic algorithm for segmenting meshes into meaningful pieces. Our approach is a clustering-based top-down hierarchical segmentation algorithm. We extend recent work on feature sensitive isotropic remeshing to generate a mesh hierarchy especially suitable for segmentation of large models with regions at multiple scales. Using integral invariants for estimation of local characteristics, our method is robust and efficient. Moreover, statistical quantities can be incorporated, allowing our approach to segment regions with different geometric characteristics or textures. *

Graphical Models, 2013

ABSTRACT Solid textures require large storage and are computationally expensive to synthesize. In... more ABSTRACT Solid textures require large storage and are computationally expensive to synthesize. In this paper, we propose a novel solid representation called gradient solids to compactly represent solid textures, including a tricubic interpolation scheme of colors and gradients for smooth variation and a region-based approach for representing sharp boundaries. We further propose a novel approach to directly synthesize gradient solid textures from exemplars. Compared to existing methods, our approach avoids the expensive step of synthesizing the complete solid textures at voxel level and produces optimized solid textures using our representation. This avoids significant amount of unnecessary computation and storage involved in the voxel-level synthesis while producing solid textures with comparable quality to the state of the art. The algorithm is much faster than existing approaches for solid texture synthesis and makes it feasible to synthesize high-resolution solid textures in full. We also propose a novel application—instant editing propagation on full solids.

Proceedings of the ACM SIGGRAPH/Eurographics Symposium on Non-Photorealistic Animation and Rendering - NPAR '11, 2011

A hidden image is a form of artistic expression in which one or more secondary objects (or scenes... more A hidden image is a form of artistic expression in which one or more secondary objects (or scenes) are hidden within a primary image. Features of the primary image, especially its edges and texture, are used to portray a secondary object. People can recognize both the primary and secondary intent in such pictures, although the time taken to do so depends on the prior experience of the viewer and the strength of the clues. Here, we present a system for creating such images. It relies on the ability of human perception to recognize an object, e.g. a human face, from incomplete edge information within its interior, rather than its outline. Our system detects edges of the object to be hidden, and then finds a place where it can be embedded within the scene, together with a suitable transformation for doing so, by optimizing an energy based on edge differences. Embedding is perfromed using a modified Poisson blending approach, which strengthens matched edges of the host image using edges of the object being embedded. We show various hidden images generated by our system.

Science China Information Sciences, 2011

This paper presents a novel method for re-rendering video in a stroke-based painterly style. Prev... more This paper presents a novel method for re-rendering video in a stroke-based painterly style. Previous methods typically place and adjust strokes on a frame by frame basis, guided by an analysis of motion vectors. Our method constructs painting patches which last for multiple frames, and paints them just once, compositing them after placing and clipping each one in each output frame. Painting patches are constructed by clustering pixels with similar motions, representing moving objects. This is done using a multi-frame window, to take account of objects which are present in consecutive frames, and which may occur a few frames apart with occlusion. The appearance of a given cluster across a sequence of frames is warped to a common reference to produce the painting patch; a global optimization of the warp is used to minimize distortion in the painting strokes. This approach outperforms prior algorithms in problem areas of the image, where flickering typically occurs, while producing comparable results elsewhere. In particular, stable strokes are produced at occlusion boundaries where objects emerge, and at image borders exposed by camera panning. A further advantage is consistent rendering of regions before and after brief occlusion, enhancing temporal stability of the output of discontiguous frames.

IEEE transactions on visualization and computer graphics, Jan 10, 2012

Harmonic functions are the critical points of a Dirichlet energy functional, the linear projectio... more Harmonic functions are the critical points of a Dirichlet energy functional, the linear projections of conformal maps. They play an important role in computer graphics, particularly for gradient-domain image processing and shape-preserving geometric computation. We propose Poisson coordinates, a novel transfinite interpolation scheme based on the Poisson integral formula, as a rapid way to estimate a harmonic function on a certain domain with desired boundary values. Poisson coordinates are an extension of the Mean Value coordinates (MVCs) which inherit their linear precision, smoothness, and kernel positivity. We give explicit formulae for Poisson coordinates in both continuous and 2D discrete forms. Superior to MVCs, Poisson coordinates are proved to be pseudo-harmonic (i.e., they reproduce harmonic functions on n-dimensional balls). Our experimental results show that Poisson coordinates have lower Dirichlet energies than MVCs on a number of typical 2D domains (particularly convex...

Science in China Series F: Information Sciences, 2009

This paper presents a novel algorithm for synthesizing animations of running water, such as water... more This paper presents a novel algorithm for synthesizing animations of running water, such as waterfalls and rivers, in the style of Chinese paintings, for applications such as cartoon making. All video frames are first registered in a common coordinate system, simultaneously segmenting the water from background and computing optical flow of the water. Taking artists' advice into account, we produce a painting structure to guide painting of brush strokes. Flow lines are placed in the water following an analysis of variance of optical flow, to cause strokes to be drawn where the water is flowing smoothly, rather than in turbulent areas: this allows a few moving strokes to depict the trends of the water flows. A variety of brush strokes is then drawn using a template determined from real Chinese paintings. The novel contributions of this paper are: a method for painting structure generation for flows in videos, and a method for stroke placement, with the necessary temporal coherence.

The Visual Computer, 2005

Video completion is the problem of automatically filling space-time holes in video sequences left... more Video completion is the problem of automatically filling space-time holes in video sequences left by the removal of unwanted objects in a scene. We solve it using texture synthesis, filling a hole inwards using three steps iteratively: we select the most promising target pixel at the edge of the hole, we find the source fragment most similar to the known part of the target's neighborhood, and we merge source and target fragments to complete the target neighborhood, reducing the size of the hole. Earlier methods were slow, due to searching the whole video data for source fragments or completing holes pixel by pixel; they also produced blurred results due to sampling and smoothing. For speed, we track moving objects, allowing us to use a much smaller search space when seeking source fragments; we also complete holes fragment by fragment instead of pixelwise. Fine details are maintained by use of a graph cut algorithm when merging source and target fragments. Further techniques ensure temporal consistency of hole filling over successive frames. Examples demonstrate the effectiveness of our method.

Computer Graphics Forum, 2014

ABSTRACT

In this paper, we have proposed a novel patchbased method for automatic completion of stereoscopi... more In this paper, we have proposed a novel patchbased method for automatic completion of stereoscopic images and the corresponding depth/disparity maps simultaneously. The missing depths are estimated in local feature space and a patch distance metric is designed to take the appearance, depth gradients and depth inconsistency into account. To ensure the proper stereopsis, we first search for the proper stereoscopic patch in both left and right images according to the distance metric, and then iteratively refine the images. Our method is capable of dealing with general scenes including both frontal-parallel and non-frontalparallel objects. Experimental results show that our method is superior to previous ones with better stereoscopically consistent content and more plausible completion.

For images, gradient domain composition methods like Poisson blending offer practical solutions f... more For images, gradient domain composition methods like Poisson blending offer practical solutions for uncertain object boundaries and differences in illumination conditions. However, adapting Poisson image blending to video faces new challenges due to the added temporal dimension. In video, the human eye is sensitive to small changes in blending boundaries across frames, and slight differences in motions of the source patch and target video. We present a novel video blending approach that tackles these problems by merging the gradient of source and target videos and optimizing a consistent blending boundary based on a user provided blending trimap for the source video. Our approach extends mean-value coordinates interpolation to support hybrid blending with a dynamic boundary while maintaining interactive performance. We also provide a user interface and source object positioning method that can efficiently deal with complex video sequences beyond the capabilities of alpha blending.

ABSTRACT This paper proposes an image-enhancement method to optimize photograph composition by re... more ABSTRACT This paper proposes an image-enhancement method to optimize photograph composition by rearranging foreground objects in the photograph. To adjust objects' positions while keeping the original scene content, we first perform a novel structure dependence analysis on the image to obtain the dependencies between all background regions. To determine the optimal positions for foreground objects, we formulate an optimization problem based on widely used heuristics for aesthetically pleasing pictures. Semantic relations between foreground objects are also taken into account during optimization. The final output is produced by moving foreground objects, together with their dependent regions, to optimal positions. The results show that our approach can effectively optimize photographs with single or multiple foreground objects without compromising the original photograph content.

: PatchNet supports interactive library-based image editing. (a) Input image and its PatchNet rep... more : PatchNet supports interactive library-based image editing. (a) Input image and its PatchNet representation. (b) The user draws a rough sketch to specify an object synthesis task. (c) Using PatchNet, the system searches a large image library in a few seconds to find the best candidate regions meeting editing constraints. (d) The user selects candidate regions to synthesize output as desired, or modifies the sketch to synthesize different object structures (lower-right).