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纹理运动的分析与合成:粒子与波。

Analysis and synthesis of textured motion: particles and waves.

作者信息

Wang Yizhou, Zhu Song-Chun

机构信息

Department of Computer Science, University of California, Los Angeles, Los Angeles, CA 90095, USA.

出版信息

IEEE Trans Pattern Anal Mach Intell. 2004 Oct;26(10):1348-63. doi: 10.1109/TPAMI.2004.76.

Abstract

Natural scenes contain a wide range of textured motion phenomena which are characterized by the movement of a large amount of particle and wave elements, such as falling snow, wavy water, and dancing grass. In this paper, we present a generative model for representing these motion patterns and study a Markov chain Monte Carlo algorithm for inferring the generative representation from observed video sequences. Our generative model consists of three components. The first is a photometric model which represents an image as a linear superposition of image bases selected from a generic and overcomplete dictionary. The dictionary contains Gabor and LoG bases for point/particle elements and Fourier bases for wave elements. These bases compete to explain the input images and transfer them to a token (base) representation with an O(10(2))-fold dimension reduction. The second component is a geometric model which groups spatially adjacent tokens (bases) and their motion trajectories into a number of moving elements--called "motons." A moton is a deformable template in time-space representing a moving element, such as a falling snowflake or a flying bird. The third component is a dynamic model which characterizes the motion of particles, waves, and their interactions. For example, the motion of particle objects floating in a river, such as leaves and balls, should be coupled with the motion of waves. The trajectories of these moving elements are represented by coupled Markov chains. The dynamic model also includes probabilistic representations for the birth/death (source/sink) of the motons. We adopt a stochastic gradient algorithm for learning and inference. Given an input video sequence, the algorithm iterates two steps: 1) computing the motons and their trajectories by a number of reversible Markov chain jumps, and 2) learning the parameters that govern the geometric deformations and motion dynamics. Novel video sequences are synthesized from the learned models and, by editing the model parameters, we demonstrate the controllability of the generative model.

摘要

自然场景包含各种各样的纹理运动现象,其特征是大量粒子和波动元素的运动,如雪、水波和舞动的草。在本文中,我们提出了一个用于表示这些运动模式的生成模型,并研究了一种马尔可夫链蒙特卡罗算法,用于从观察到的视频序列中推断出生成表示。我们的生成模型由三个部分组成。第一部分是光度模型,它将图像表示为从通用且超完备字典中选择的图像基的线性叠加。该字典包含用于点/粒子元素的Gabor和LoG基以及用于波动元素的傅里叶基。这些基竞争以解释输入图像,并将它们转换为具有O(10(2))倍降维的令牌(基)表示。第二部分是几何模型,它将空间上相邻的令牌(基)及其运动轨迹分组为多个移动元素——称为“运动子”。运动子是时空上的可变形模板,表示一个移动元素,如飘落的雪花或飞翔的鸟。第三部分是动态模型,它表征粒子、波及其相互作用的运动。例如,漂浮在河流中的粒子物体(如树叶和球)的运动应与波浪的运动耦合。这些移动元素的轨迹由耦合马尔可夫链表示。动态模型还包括运动子的出生/死亡(源/汇)的概率表示。我们采用随机梯度算法进行学习和推理。给定一个输入视频序列,该算法迭代两个步骤:1)通过多次可逆马尔可夫链跳跃计算运动子及其轨迹,2)学习控制几何变形和运动动力学的参数。从学习到的模型中合成新的视频序列,并且通过编辑模型参数,我们展示了生成模型的可控性。

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