人物真实皮肤材质实时渲染研究
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摘要
如今,在电影行业,借助电脑数字技术营造的各种影视特效,不断地制造出一部部优秀的电影;在电子游戏行业,同样是借助电脑图形渲染技术创作出无数的经典游戏。然而这两种媒介各有缺点,交互电影这个全新概念恰恰能弥补电影单线故事情节与游戏画面不够真实精致的缺点。它既能保证电影的逼真效果,又有游戏的交互性,多故事性和多结局性。而这关键技术之一便是实时交互渲染技术。
同时,这项技术又涉及不同对象的渲染,特别是强调物体材质质感的真实性,如金属,砖瓦,水等质感各不相同。以往在实时渲染中实现这些不同对象材质的效果时,仅仅通过贴图纹理来区别,在其视觉效果上少有深入的研究。
其中,人物皮肤可谓是最复杂的效果,这种半透明材质一直是预渲染作品方面研究的高级课题,如何表现次表面散射3S(Sub-Surface Scattering)效果研究已经有了不少研究成果。但是由于这类材质光照的复杂性,此类研究成果依然有由于计算复杂、计算量大而渲染速度慢的缺点,从而很难在交互媒介上得到应用。
如何近似地将这效果模拟应用于交互电影中的人物上,并且高效地进行实时演算成为极其有意义的工作。
有鉴于此,本文通过长期在游戏行业工作经验的积累,借助虚幻3游戏引擎,通过大量的测试方案对比,以及参数的调试,在保证效率的前提下获得比较满意,接近电影品质的人物皮肤材质效果。
本文的研究重点及主要成果有:
1.确立了逼真皮肤表面几何细节制作有效的流程。Normal Map(法线贴图)的应用是平衡渲染效率和最终质量最为有效的方法,研究如何基于三维软件成功得到了最优化的实时渲染模型,以及通过合理的多边形曲面布线分配获得比较完美的法线贴图。
2.掌握了光照模型的一些基本概念,确定了皮肤基础质感的实现方法。并且通过测试研究了科学计算节点表达式、多维常量表达式、贴图样本表达式和贴图坐标表达式的工作原理。
3.本文通过复合节点表达式形成的节点网分别对角色脸部Diffuse(漫反射)效果,多层遮罩的Normal(法线)效果以及Specular(高光)效果实践,尝试了不同的参数进行对比,总结并确定了一套效果较正确的设置。并且综合运用到整个材质网络中,得到基础皮肤材质效果。
4.对发生次表面散射现象的半透明物体从视觉效果的角度进行了较为详细的讨论。通过多种模拟次表面散射现象的渲染图片的对比,真正了解次表面散射的视觉效果。
5.拟定了3套模拟次表面反射的半透明效果实现方案,从最简单的算法到更真实的算法,分别是emissive(自发光)算法,Fresnel(菲涅尔)以及Transmission(传播)。在不同灯光角度下通过大量调试比较透光度,指出了每个算法的优缺点。最终确立了运用Transmission(传播)的算法方式,高效地制作出非常贴近Offline(离线渲染)次表面散射效果的材质。
6.运用2种反射技术,分别是单贴图反射和Cube Map(立方体环境反射),实现真实眼球质感表现。分析了眼球材质与人体其他部位材质的不同,反射的特征是视觉上表现眼球材质效果的重要因素。
Nowadays,in movie industry,by using digital techniques to create all kinds of visual special effects, constantly produce many excellent movies;In video game industry,is also using computing graphics rendering techniques to create innumerable classic games. However, these two media each have shortages. Interactive movie, the brand-new media can compensate for their shortages which single storyline for movie and low quality visual effects for game rendering. It provides movie's lifelike effect and game's interactivity, multi narrative and multi ending. And one of the key techniques is real-time rendering.
Meanwhile,this technique relate to different objects rendering, Especially emphasizing on real tactile sensation, such as the different materials of metal, brick and water. When deal with this kind of effects, just use textures to distinguish them before, lack of in-depth research on its visual effects.
Among them,the character skin effect is the most complex part. This translucent material has always been an advanced topic in pre-render field. Scientists have many experiences and achievements on how to simulate 3S(Sub-Surface Scattering). But it's hard to apply to interactive Medias directly because of shortage: complex shader, large amount of calculation and low efficiency.
How to approximate to simulate this kind of effect on characters in activity movies and real-time rendering with high efficient will be a significant job.
In view of this, this paper through long term of game industry experiences, making large number of tests, comparisons and modification, simulate the character skin effect which close to movie quality and with acceptable efficiency.
In this paper, the research focuses and main achievements of this thesis are as follow:
Establish the workflow about the character details producing. Using normal map is the best way to balance the efficiency and final quality. Research how to achieve the optimized models base on 3d software. And achieve perfect normal maps according to reasonable polygon topology.
Master some basic concepts of illumination models, and determine the implementation methods of character basic skin. Try and research the working principle of scientific expressions, multi vector expressions, texture sample expressions and texture coordinate expressions
The paper through composite node expression nets, simulate the diffuse, multi-mask layer normal and specular effects. By comparison of different parameter settings set up a series of correct settings. And then apply to whole material net to get realistic basic skin shader.
Discuss about the visual effects of Sub-Surface Scattering objects. Real know the effects of 3S through comparison of a variety of images which rendered by 3S techniques.
Draw up 3 sets of scheme to simulate translucent effect of sub surface scatter from simplest to more realistic methods. They are Emissive algorithm, Fresnel algorithm and Transmission algorithm. Compare and modify the transmittance. Point out the shortage for each. The conclusion is: transmission algorithm can produce the effect which is very close to offline 3S rendering.
By two reflection techniques (single image based reflection and cube map reflection) to simulate realistic eyeball. Analyzing the difference between eyeball effects and other parts, achieve the conclusion that the reflection effect is key factor.
同时,这项技术又涉及不同对象的渲染,特别是强调物体材质质感的真实性,如金属,砖瓦,水等质感各不相同。以往在实时渲染中实现这些不同对象材质的效果时,仅仅通过贴图纹理来区别,在其视觉效果上少有深入的研究。
其中,人物皮肤可谓是最复杂的效果,这种半透明材质一直是预渲染作品方面研究的高级课题,如何表现次表面散射3S(Sub-Surface Scattering)效果研究已经有了不少研究成果。但是由于这类材质光照的复杂性,此类研究成果依然有由于计算复杂、计算量大而渲染速度慢的缺点,从而很难在交互媒介上得到应用。
如何近似地将这效果模拟应用于交互电影中的人物上,并且高效地进行实时演算成为极其有意义的工作。
有鉴于此,本文通过长期在游戏行业工作经验的积累,借助虚幻3游戏引擎,通过大量的测试方案对比,以及参数的调试,在保证效率的前提下获得比较满意,接近电影品质的人物皮肤材质效果。
本文的研究重点及主要成果有:
1.确立了逼真皮肤表面几何细节制作有效的流程。Normal Map(法线贴图)的应用是平衡渲染效率和最终质量最为有效的方法,研究如何基于三维软件成功得到了最优化的实时渲染模型,以及通过合理的多边形曲面布线分配获得比较完美的法线贴图。
2.掌握了光照模型的一些基本概念,确定了皮肤基础质感的实现方法。并且通过测试研究了科学计算节点表达式、多维常量表达式、贴图样本表达式和贴图坐标表达式的工作原理。
3.本文通过复合节点表达式形成的节点网分别对角色脸部Diffuse(漫反射)效果,多层遮罩的Normal(法线)效果以及Specular(高光)效果实践,尝试了不同的参数进行对比,总结并确定了一套效果较正确的设置。并且综合运用到整个材质网络中,得到基础皮肤材质效果。
4.对发生次表面散射现象的半透明物体从视觉效果的角度进行了较为详细的讨论。通过多种模拟次表面散射现象的渲染图片的对比,真正了解次表面散射的视觉效果。
5.拟定了3套模拟次表面反射的半透明效果实现方案,从最简单的算法到更真实的算法,分别是emissive(自发光)算法,Fresnel(菲涅尔)以及Transmission(传播)。在不同灯光角度下通过大量调试比较透光度,指出了每个算法的优缺点。最终确立了运用Transmission(传播)的算法方式,高效地制作出非常贴近Offline(离线渲染)次表面散射效果的材质。
6.运用2种反射技术,分别是单贴图反射和Cube Map(立方体环境反射),实现真实眼球质感表现。分析了眼球材质与人体其他部位材质的不同,反射的特征是视觉上表现眼球材质效果的重要因素。
Nowadays,in movie industry,by using digital techniques to create all kinds of visual special effects, constantly produce many excellent movies;In video game industry,is also using computing graphics rendering techniques to create innumerable classic games. However, these two media each have shortages. Interactive movie, the brand-new media can compensate for their shortages which single storyline for movie and low quality visual effects for game rendering. It provides movie's lifelike effect and game's interactivity, multi narrative and multi ending. And one of the key techniques is real-time rendering.
Meanwhile,this technique relate to different objects rendering, Especially emphasizing on real tactile sensation, such as the different materials of metal, brick and water. When deal with this kind of effects, just use textures to distinguish them before, lack of in-depth research on its visual effects.
Among them,the character skin effect is the most complex part. This translucent material has always been an advanced topic in pre-render field. Scientists have many experiences and achievements on how to simulate 3S(Sub-Surface Scattering). But it's hard to apply to interactive Medias directly because of shortage: complex shader, large amount of calculation and low efficiency.
How to approximate to simulate this kind of effect on characters in activity movies and real-time rendering with high efficient will be a significant job.
In view of this, this paper through long term of game industry experiences, making large number of tests, comparisons and modification, simulate the character skin effect which close to movie quality and with acceptable efficiency.
In this paper, the research focuses and main achievements of this thesis are as follow:
Establish the workflow about the character details producing. Using normal map is the best way to balance the efficiency and final quality. Research how to achieve the optimized models base on 3d software. And achieve perfect normal maps according to reasonable polygon topology.
Master some basic concepts of illumination models, and determine the implementation methods of character basic skin. Try and research the working principle of scientific expressions, multi vector expressions, texture sample expressions and texture coordinate expressions
The paper through composite node expression nets, simulate the diffuse, multi-mask layer normal and specular effects. By comparison of different parameter settings set up a series of correct settings. And then apply to whole material net to get realistic basic skin shader.
Discuss about the visual effects of Sub-Surface Scattering objects. Real know the effects of 3S through comparison of a variety of images which rendered by 3S techniques.
Draw up 3 sets of scheme to simulate translucent effect of sub surface scatter from simplest to more realistic methods. They are Emissive algorithm, Fresnel algorithm and Transmission algorithm. Compare and modify the transmittance. Point out the shortage for each. The conclusion is: transmission algorithm can produce the effect which is very close to offline 3S rendering.
By two reflection techniques (single image based reflection and cube map reflection) to simulate realistic eyeball. Analyzing the difference between eyeball effects and other parts, achieve the conclusion that the reflection effect is key factor.
引文
[1] Interactive movie,http://en.wikipedia.org/wiki/Interactive_movie.
[2] Bernard Mendiburu,3D Movie Making: Stereoscopic Digital Cinema from Script to Screen,Focal Press,May 6,2009.
[3]指环王原画图集, http://image.baidu.com/i?tn=baiduimage&ct=201326592&lm=-1&cl=2&fr=ala0&word=%D6%B8%BB%B7%CD%F5%D4%AD%BB%AD.
[4] John Brown,Sculpting the Femme Fatale, The Techniques of John Brown,Volume 6, 2008.
[5]张向春,三维建模的艺术与速度,清华大学出版社, 2010-4.
[6] (美)克维克,笑傲次世代:高级游戏角色3D制作宝典,化学工业出版社,2011.
[7] Rohan Coelho and Maher Hawash,DirectX(R),RDX,RSX,and MMX(TM) Technology:A Jumpstart Guide to High Performance APIs,Addison-Wesley Professional,Jan 9,1998.
[8] Paul Cockshott and Kenneth Renfrew,SIMD Programming Manual for Linux and Windows (Springer Professional Computing),Springer,1st ed. Softcover of orig. ed. Dec 15,2010.
[9] Hubert Nguyen,GPU Gems 3,Addison-Wesley Professional,Aug 12,2007.
[10] Mike McShaffry,Computer Physics Engines:Collision Detection,Soft Body Dynamics,Cuda,Physx,Physics Engine,Bullet,Physics Processing Unit. Books LLC,2003.
[11] SIGGRAPH 2009 sessions,Art papers, http://www.siggraph.org/s2009/sessions/index.php.
[12]林大为,3D游戏角色制作,上海人民美术出版社,2010-6.
[13]朱咏,万国华,周宇峰,绘画入门正规训练——速写,江西美术出版社,2004-3.
[14] (美)斯潘塞(Spencer,S.), ZBrush角色塑造:高级数字雕刻,人民邮电出版社,2009-6.
[15]熊绍庚,人体解剖学(美术技法理论)/高等院校美术专业系列教材,岭南美术出版社,3004-3.
[16] UV坐标基础知识, http://translate.google.com.hk/translate?hl=zh-CN&langpair=en|zh-CN&u=http://www.rozengain.com/blog/2007/08/26/uv-coordinate-basics/.
[17] Surface Patterning with UV Coordinates, http://lmnts.lmnarchitects.com/parametrics/surface-uv-coordinates/.
[18] St-Laurent Sebastien and Engel Wolfgang, the COMPLETE Effect and HLSL Guide,Paradoxal Press,Jul 1,2005
[19] DX9的光照模型,http://www.gamengines.com/simple/?t1712.html.
[20] Matt Pharr,Greg Humphreys Physically:Based Rendering,Second Edition, From Theory To Implementation,Morgan Kaufmann,2008.
[21]刘建科,超写实艺术:3ds max/VRay家装设计渲染篇,电子工业出版社,2009-1.
[22] Sebastien St-Laurent,Shaders for Game Programmers and Artists (Premier Press Game Development),Course Technology PTR,2004.
[23] Wolfgang Engel,GPU Pro:Advanced Rendering Techniques,A K Peters/CRC Press,2010.
[24] Frank Luna,Introduction to 3D Game Programming with Direct X 9.0c:A Shader Approach (Wordware Game and Graphics Library),Jones & Bartlett Publishers,June 25,2006.
[25] Frank D. Luna,Introduction to 3D Game Programming with DirectX 10,Jones & Bartlett Publishers,October 25, 2008.
[26]张永昌,质感传奇-3ds Max写实渲染完全实例教程,科学出版社,2010-5.
[27] GPU加速Diffuse Cube Map经典计算, http://game.chinaitlab.com/devdoc/30004.html.
[28]眼球的立体结构, http://amuseum.cdstm.cn/AMuseum/perceptive/page_3_eye/page_3_1_0.htm.
[2] Bernard Mendiburu,3D Movie Making: Stereoscopic Digital Cinema from Script to Screen,Focal Press,May 6,2009.
[3]指环王原画图集, http://image.baidu.com/i?tn=baiduimage&ct=201326592&lm=-1&cl=2&fr=ala0&word=%D6%B8%BB%B7%CD%F5%D4%AD%BB%AD.
[4] John Brown,Sculpting the Femme Fatale, The Techniques of John Brown,Volume 6, 2008.
[5]张向春,三维建模的艺术与速度,清华大学出版社, 2010-4.
[6] (美)克维克,笑傲次世代:高级游戏角色3D制作宝典,化学工业出版社,2011.
[7] Rohan Coelho and Maher Hawash,DirectX(R),RDX,RSX,and MMX(TM) Technology:A Jumpstart Guide to High Performance APIs,Addison-Wesley Professional,Jan 9,1998.
[8] Paul Cockshott and Kenneth Renfrew,SIMD Programming Manual for Linux and Windows (Springer Professional Computing),Springer,1st ed. Softcover of orig. ed. Dec 15,2010.
[9] Hubert Nguyen,GPU Gems 3,Addison-Wesley Professional,Aug 12,2007.
[10] Mike McShaffry,Computer Physics Engines:Collision Detection,Soft Body Dynamics,Cuda,Physx,Physics Engine,Bullet,Physics Processing Unit. Books LLC,2003.
[11] SIGGRAPH 2009 sessions,Art papers, http://www.siggraph.org/s2009/sessions/index.php.
[12]林大为,3D游戏角色制作,上海人民美术出版社,2010-6.
[13]朱咏,万国华,周宇峰,绘画入门正规训练——速写,江西美术出版社,2004-3.
[14] (美)斯潘塞(Spencer,S.), ZBrush角色塑造:高级数字雕刻,人民邮电出版社,2009-6.
[15]熊绍庚,人体解剖学(美术技法理论)/高等院校美术专业系列教材,岭南美术出版社,3004-3.
[16] UV坐标基础知识, http://translate.google.com.hk/translate?hl=zh-CN&langpair=en|zh-CN&u=http://www.rozengain.com/blog/2007/08/26/uv-coordinate-basics/.
[17] Surface Patterning with UV Coordinates, http://lmnts.lmnarchitects.com/parametrics/surface-uv-coordinates/.
[18] St-Laurent Sebastien and Engel Wolfgang, the COMPLETE Effect and HLSL Guide,Paradoxal Press,Jul 1,2005
[19] DX9的光照模型,http://www.gamengines.com/simple/?t1712.html.
[20] Matt Pharr,Greg Humphreys Physically:Based Rendering,Second Edition, From Theory To Implementation,Morgan Kaufmann,2008.
[21]刘建科,超写实艺术:3ds max/VRay家装设计渲染篇,电子工业出版社,2009-1.
[22] Sebastien St-Laurent,Shaders for Game Programmers and Artists (Premier Press Game Development),Course Technology PTR,2004.
[23] Wolfgang Engel,GPU Pro:Advanced Rendering Techniques,A K Peters/CRC Press,2010.
[24] Frank Luna,Introduction to 3D Game Programming with Direct X 9.0c:A Shader Approach (Wordware Game and Graphics Library),Jones & Bartlett Publishers,June 25,2006.
[25] Frank D. Luna,Introduction to 3D Game Programming with DirectX 10,Jones & Bartlett Publishers,October 25, 2008.
[26]张永昌,质感传奇-3ds Max写实渲染完全实例教程,科学出版社,2010-5.
[27] GPU加速Diffuse Cube Map经典计算, http://game.chinaitlab.com/devdoc/30004.html.
[28]眼球的立体结构, http://amuseum.cdstm.cn/AMuseum/perceptive/page_3_eye/page_3_1_0.htm.