枫叶老化虚拟方法与关键技术研究
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摘要
叶子是体现植物形态之美的一个重要器官，是植物可视化模拟的关键部分。植物叶子的虚拟仿真对数字农业、远程教育、电影特效及游戏制作等领域均具有重要意义。然而，叶子拥有复杂的内外结构，且随着季节与气候的交替变化，其形态与纹理变化十分显著，导致叶子的建模仿真及其动画制作变得十分困难。针对已有研究很少关注叶子在不同季节和环境下的形态特征及颜色纹理变化模拟等问题，论文以元宝枫的叶子为主要研究对象，研究了植物叶子三维建模方法，植物叶子卷曲变形动态仿真方法，植物叶子颜色纹理动态变化模拟方法，并设计开发了虚拟植物叶子老化的软件平台。主要研究内容和结论如下：
（1）研究了基于叶子图像重建叶子三维模型的方法，提出了一种根据叶子轮廓，自动生成主、二级叶脉的方法，较好地模拟了叶脉在叶子轮廓内的分布，解决了传统的叶脉生成方法引入过多手动交互的问题，同时重点探讨了利用双面纹理映射技术对叶子模型进行颜色渲染的方法，构建了接近照片的叶子可视化模型。
（2）提出了基于叶脉骨架的旋转模型，以枫叶和玉兰叶子为研究对象，利用该模型仿真了叶子多种形态的卷曲变形及褶皱效果。和以往的模型相比，该模型没有进行复杂的力学分析或引入过多的生物学理论，故算法的运行速度（大约16~17fps）接近实时性要求，叶子变形动画效果流畅，模拟的叶子变形效果较为真实。
（3）基于叶子老化的假设条件，建立了植物叶子内叶绿素、类胡萝卜素和花色素伴随叶子老化而变化的数学模型，以及这3种色素与HSI颜色模型之间的数学关系，并充分考虑主脉、二级叶脉、叶柄点及光照对叶子老化的影响，从单片叶子模拟角度出发，仿真了枫叶在秋季的颜色纹理变化，即叶子呈现由绿变黄，再变红的动态变化过程，仿真效果具有一定的真实性，算法可在1分钟内再现秋季枫叶的颜色纹理变化。
（4）设计开发了基于PC平台的植物叶子老化仿真系统。利用该系统可基于叶子图片构建叶子的三维模型，交互输入变形控制参数，可获得叶子各种形态的变形效果，设定颜色及形态变化的动画帧数，可动态模拟叶子各种程度的老化过程。系统的开发设计与参数L系统相结合，构建了简单的叶子簇，模拟了多片叶子的形态、纹理变化过程。系统仿真效果表明，本文提出的方法可以较真实地再现叶子在秋季的形态及纹理变化。
Leaves are essential parts to portray the natural beauty of plants, and play the pivotalrole in plants visualization and simulations. Plant leaves simulations are of criticalsignificance for digital agriculture, online education, film special effects and games design.However, leaves have complicated external morphology and internal construction, and theirshapes and textures change greatly with season and weather, all of which make the simulationand animation of leaves become quite difficult. As the previous research paid little attentionto the simulations of the morphology and color changes of leaves in different circumstancesand seasons, this dissertation took maple leaves as the main research object, and studied thethree-dimensional modeling method of plant leaves, dynamic simulation methods of curlyplant leaves and texture changes of plant leaves. Then we designed and developed thevisualization system for simulating the dynamic process of plant leaves ageing. The mainwork and conclusions are as follows:
(1) We studied the method to generate three-dimensional leaf models based on leafimages, and proposed the method to build primary and secondary veins automaticallyaccording to the leaf silhouette, which can properly simulate veins distribution in the leafsilhouette and solve the problem that traditional approaches generating veins usually requiretoo much manual interactions. Meanwhile, how to render leaf models by double sided texturemapping techniques was discussed, by which the three-dimensional leaf models analogous toleaf photos were constructed.
(2) The venation-skeleton based Rotation-Model is proposed in this paper. Maple andmagnolia leaves were used for studying, and various curly and folded leaves’ models weresimulated by the Rotation-Model. Compared with previous approaches, Rotation-Model doesnot have complicated mechanical analysis or introduce excessive biological theory, whichmakes the running speed (about16~17fps) of our algorithm approach the real-timerequirement, and the animation of leaves deformation is fluid. Further, the simulation resultsof curly plant leaves are quite realistic by our method.
(3) Based on the assumptions about leaves ageing, we built the mathematical model forthe chlorophyll, the carotenoid, the anthocyanin in leaves, the amounts of which change with leaves ageing process, as well as the mathematical relationships between these three pigmentsand the HSI color model. Additionally, the influences of primary veins, secondary veins, thepetiole and the light were taken into account for simulating leaves ageing, and from theprospective of one single leaf simulation, we modeled the color changes of maple leavesduring ageing in autumn, which showed the dynamic process from green to yellow and thento red. The simulation results are realistic to a certain degree, and the algorithm could showthe color changes of a maple leaf in autumn within1minutes.
(4) We designed and explored the virtual system of plant leaves ageing on the basis ofPC platform. The three-dimensional leaf model could be generated based on the leaf imageby our system. Then, we could obtain all forms of leaf deformation through interactivelyinputting parameters controlling leaves deformation. After setting the frames of animation forcolor and morphology changes, we could simulate different kinds of leaves ageing effectsdynamically. The design of our system was combined with parameterized L-systems, bywhich the simple leaf clusters were built; therefore, the morphology and color changes forseveral leaves were simulated. The simulation results of our system indicate that the proposedmethods in this dissertation could realistically describe the shape and color changes of leavesin autumn.
（1）研究了基于叶子图像重建叶子三维模型的方法，提出了一种根据叶子轮廓，自动生成主、二级叶脉的方法，较好地模拟了叶脉在叶子轮廓内的分布，解决了传统的叶脉生成方法引入过多手动交互的问题，同时重点探讨了利用双面纹理映射技术对叶子模型进行颜色渲染的方法，构建了接近照片的叶子可视化模型。
（2）提出了基于叶脉骨架的旋转模型，以枫叶和玉兰叶子为研究对象，利用该模型仿真了叶子多种形态的卷曲变形及褶皱效果。和以往的模型相比，该模型没有进行复杂的力学分析或引入过多的生物学理论，故算法的运行速度（大约16~17fps）接近实时性要求，叶子变形动画效果流畅，模拟的叶子变形效果较为真实。
（3）基于叶子老化的假设条件，建立了植物叶子内叶绿素、类胡萝卜素和花色素伴随叶子老化而变化的数学模型，以及这3种色素与HSI颜色模型之间的数学关系，并充分考虑主脉、二级叶脉、叶柄点及光照对叶子老化的影响，从单片叶子模拟角度出发，仿真了枫叶在秋季的颜色纹理变化，即叶子呈现由绿变黄，再变红的动态变化过程，仿真效果具有一定的真实性，算法可在1分钟内再现秋季枫叶的颜色纹理变化。
（4）设计开发了基于PC平台的植物叶子老化仿真系统。利用该系统可基于叶子图片构建叶子的三维模型，交互输入变形控制参数，可获得叶子各种形态的变形效果，设定颜色及形态变化的动画帧数，可动态模拟叶子各种程度的老化过程。系统的开发设计与参数L系统相结合，构建了简单的叶子簇，模拟了多片叶子的形态、纹理变化过程。系统仿真效果表明，本文提出的方法可以较真实地再现叶子在秋季的形态及纹理变化。
Leaves are essential parts to portray the natural beauty of plants, and play the pivotalrole in plants visualization and simulations. Plant leaves simulations are of criticalsignificance for digital agriculture, online education, film special effects and games design.However, leaves have complicated external morphology and internal construction, and theirshapes and textures change greatly with season and weather, all of which make the simulationand animation of leaves become quite difficult. As the previous research paid little attentionto the simulations of the morphology and color changes of leaves in different circumstancesand seasons, this dissertation took maple leaves as the main research object, and studied thethree-dimensional modeling method of plant leaves, dynamic simulation methods of curlyplant leaves and texture changes of plant leaves. Then we designed and developed thevisualization system for simulating the dynamic process of plant leaves ageing. The mainwork and conclusions are as follows:
(1) We studied the method to generate three-dimensional leaf models based on leafimages, and proposed the method to build primary and secondary veins automaticallyaccording to the leaf silhouette, which can properly simulate veins distribution in the leafsilhouette and solve the problem that traditional approaches generating veins usually requiretoo much manual interactions. Meanwhile, how to render leaf models by double sided texturemapping techniques was discussed, by which the three-dimensional leaf models analogous toleaf photos were constructed.
(2) The venation-skeleton based Rotation-Model is proposed in this paper. Maple andmagnolia leaves were used for studying, and various curly and folded leaves’ models weresimulated by the Rotation-Model. Compared with previous approaches, Rotation-Model doesnot have complicated mechanical analysis or introduce excessive biological theory, whichmakes the running speed (about16~17fps) of our algorithm approach the real-timerequirement, and the animation of leaves deformation is fluid. Further, the simulation resultsof curly plant leaves are quite realistic by our method.
(3) Based on the assumptions about leaves ageing, we built the mathematical model forthe chlorophyll, the carotenoid, the anthocyanin in leaves, the amounts of which change with leaves ageing process, as well as the mathematical relationships between these three pigmentsand the HSI color model. Additionally, the influences of primary veins, secondary veins, thepetiole and the light were taken into account for simulating leaves ageing, and from theprospective of one single leaf simulation, we modeled the color changes of maple leavesduring ageing in autumn, which showed the dynamic process from green to yellow and thento red. The simulation results are realistic to a certain degree, and the algorithm could showthe color changes of a maple leaf in autumn within1minutes.
(4) We designed and explored the virtual system of plant leaves ageing on the basis ofPC platform. The three-dimensional leaf model could be generated based on the leaf imageby our system. Then, we could obtain all forms of leaf deformation through interactivelyinputting parameters controlling leaves deformation. After setting the frames of animation forcolor and morphology changes, we could simulate different kinds of leaves ageing effectsdynamically. The design of our system was combined with parameterized L-systems, bywhich the simple leaf clusters were built; therefore, the morphology and color changes forseveral leaves were simulated. The simulation results of our system indicate that the proposedmethods in this dissertation could realistically describe the shape and color changes of leavesin autumn.
引文
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迟小羽,盛斌,陈彦云,吴恩华.2009a.基于物理的植物叶子形态变化过程仿真造型.计算机学报,32(2):221-230
迟小羽，盛斌，杨猛，陈彦云，吴恩华.2009b.秋季植物叶子表观的模拟.软件学报,20(3):703-712
郭焱,李保国.2001.虚拟植物的研究进展.科学通报,46(4):273-280
方小勇,郭新宇,王丹虹,孙广宇.2006.黄瓜叶几何造型研究.计算机工程与应用,(32):183-185
何东健,耿楠,张义宽.2003.数字图像处理，西安：西安电子科技大学出版社:30-32,206-207
胡少军.2006.越冬前期小麦生长可视化技术研究[硕士学位论文].杨凌:西北农林科技大学
胡少军,何东健,耿楠,郭亚红.2007.基于图像处理的小麦叶片形态的三维重建.农业工程学报,23(1):150-154
胡伟.2009.苹果果实变质过程虚拟关键技术研究[硕士学位论文].杨凌:西北农林科技大学
焦少慧,杨刚, Heng Pheng-Ann，吴恩华.2010.基于时变纹元的真实感草地枯萎模拟,软件学报,21(9):2224-2236.
康丽,苏中滨,郑萍,李彦锋.2006.基于L系统的植物叶脉模拟的研究.农机化研究,(7):180-181
雷蕾,郭新宇,周淑秋.2004.基于粒子系统思想的叶片纹理构造.计算机工程与应用,36:218-219
李云峰.2005.叶图像提取研究及虚拟植物可视化实现[博士学位论文].重庆:重庆大学
刘钢,彭群生,鲍虎军.2005.基于图像建模技术研究综述与展望.计算机辅助设计与图形学,17(1)：18-27
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