基于物理的次表面散射繪制方法
發(fā)布時(shí)間：2018-09-18 11:31
【摘要】：隨著圖形學(xué)技術(shù)的發(fā)展以及計(jì)算機(jī)運(yùn)算能力的提升,真實(shí)感渲染技術(shù)在影視動(dòng)漫、視頻游戲、模擬仿真等領(lǐng)域的應(yīng)用越來越廣泛。具有高度真實(shí)感的材質(zhì)在整個(gè)渲染過程中具有重要作用,目前像PRman、Arnold等主流的電影級商業(yè)渲染器都具有自己的材質(zhì)系統(tǒng),藝術(shù)家通過組合各種材質(zhì)并調(diào)節(jié)它們的參數(shù),就可以使用這些渲染器渲染出照片級真實(shí)感的圖片,最終這些令人震撼的畫面制作成電影呈現(xiàn)給了觀眾。商業(yè)渲染器提供的材質(zhì)可以分為兩類,其中可用于模擬玻璃、塑料、不銹鋼等硬質(zhì)表面的基本材質(zhì)因?yàn)閷?shí)現(xiàn)難度低且發(fā)展較早已經(jīng)日趨成熟,而像皮膚這種特殊的具有次表面散射特點(diǎn)的材質(zhì)因?yàn)閷?shí)現(xiàn)難度高且發(fā)展起步晚一直是衡量一個(gè)真實(shí)感渲染器優(yōu)劣的重要因素。另一方面,因?yàn)樗蟹莻鲗?dǎo)的有機(jī)體都具有次表面散射特性,所以這種材質(zhì)在影視和游戲中的應(yīng)用非常廣泛。使用純物理模擬的次表面散射材質(zhì)因?yàn)槭諗克俣忍鵁o法實(shí)際應(yīng)用,然后近似模擬的次表面散射材質(zhì)便應(yīng)運(yùn)而生。但這些近似方法各有優(yōu)缺點(diǎn),有的渲染速度快但是流程復(fù)雜效果一般,有的流程簡單效果一流但是渲染速度較慢,而目前關(guān)于實(shí)時(shí)次表面散射的研究很少,徐昆提出的方法只能適用于物體的光照環(huán)境不變的情形。本文深入研究了兩種不同的次表面散射算法,并以renderman規(guī)范渲染器為平臺,就如何在該類渲染器下實(shí)現(xiàn)次表面散射材質(zhì)進(jìn)行了深入研究,最終給出一套完整實(shí)現(xiàn),并對實(shí)驗(yàn)結(jié)果進(jìn)行了對比和分析。然后,結(jié)合前面方法,提出了一種基于GPU的實(shí)時(shí)次表面散射算法,該方法分為兩步,第一步利用BSSRDF的重要性采樣方法得到每個(gè)著色點(diǎn)所依賴的采樣點(diǎn)紋理坐標(biāo),并將它們存入貼圖中,第二步計(jì)算每個(gè)著色點(diǎn)時(shí),根據(jù)上一步得到的紋理坐標(biāo)將物體表面的直接光照進(jìn)行融合即得到著色點(diǎn)顏色。本文的主要工作有：1,研究基于點(diǎn)云的快速分層次表面散射,對在REYES架構(gòu)渲染器中實(shí)現(xiàn)該方法時(shí)的點(diǎn)云分布進(jìn)行優(yōu)化,結(jié)合多層次表面散射算法,提出了一種帶有表面粗糙度的快速分層次表面散射算法,可以模擬光滑的玉石。2,提出了一種在renderman規(guī)范渲染器中實(shí)現(xiàn)基于BSSRDF重要性采樣次表面散射算法的方法,提出了一種簡單高效的BVH樹構(gòu)建方法用于光線與場景求交,并對之前渲染器中射線與四邊形求交算法進(jìn)行改進(jìn)。3,提出了一種通過將BSSRDF的重要性采樣點(diǎn)預(yù)計(jì)算并存入貼圖的方式實(shí)現(xiàn)基于GPU的實(shí)時(shí)次表面散射的算法,該方法首次允許物體的光照環(huán)境可以實(shí)時(shí)改變。
[Abstract]:With the development of graphics technology and the improvement of computer computing ability, realistic rendering technology is more and more widely used in video animation, video games, simulation and other fields. Materials with a high degree of realism play an important role in the whole rendering process. At present, mainstream commercial renderings such as PRman,Arnold have their own material systems, and artists combine various materials and adjust their parameters. You can use these renderings to render photo-level realistic images, and eventually these stunning images are made into movies and presented to the audience. The commercial renderer offers two types of materials, one of which can be used to simulate hard surfaces such as glass, plastic, stainless steel and so on, because of the low difficulty of implementation and the early development of the basic materials, they have become more and more mature. The special material with subsurface scattering such as skin has been an important factor to evaluate the quality of a realistic renderer because of its high implementation difficulty and late development. On the other hand, because all non-conducting organisms have subsurface scattering properties, this material is widely used in film, television and games. Due to the slow convergence rate of the subsurface scattering material simulated by pure physics, it can not be applied in practice, and then the subsurface scattering material which is similar to the simulated subsurface scattering material emerges as the times require. However, these approximate methods have their own advantages and disadvantages. Some of them have fast rendering speed but generally complex process effects, while some simple process effects are first class but rendering speed is relatively slow. However, there are few researches on real-time subsurface scattering at present. The method proposed by Xu Kun can only be applied to the case where the illumination environment of an object is invariant. In this paper, two different subsurface scattering algorithms are studied in depth, and how to realize the subsurface scattering material under the renderman standard renderer is studied deeply, and a complete set of implementation is given. The experimental results are compared and analyzed. Then, a real-time subsurface scattering algorithm based on GPU is proposed, which is divided into two steps. In the first step, the texture coordinates of each coloring point are obtained by using the importance sampling method of BSSRDF. They are stored in the map. In the second step, when each coloring point is calculated, the coloring point color is obtained by merging the direct illumination of the object surface according to the texture coordinates obtained from the previous step. The main work of this paper is: 1. The fast hierarchical surface scattering based on point cloud is studied. The distribution of point cloud in REYES architecture renderer is optimized, and the multi-layer surface scattering algorithm is combined. In this paper, a fast hierarchical surface scattering algorithm with surface roughness is proposed, which can simulate smooth jade. A method is proposed to realize the subsurface scattering algorithm based on BSSRDF importance sampling in renderman renderer. In this paper, a simple and efficient BVH tree construction method is proposed for the intersection of light and scene. By improving the intersection algorithm of ray and quadrilateral in the previous renderer, a real-time subsurface scattering algorithm based on GPU is proposed by pre-calculating the important sampling points of BSSRDF and storing them into the map. For the first time, the method allows the illumination of objects to change in real time.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TP391.41
本文編號：2247773
[Abstract]:With the development of graphics technology and the improvement of computer computing ability, realistic rendering technology is more and more widely used in video animation, video games, simulation and other fields. Materials with a high degree of realism play an important role in the whole rendering process. At present, mainstream commercial renderings such as PRman,Arnold have their own material systems, and artists combine various materials and adjust their parameters. You can use these renderings to render photo-level realistic images, and eventually these stunning images are made into movies and presented to the audience. The commercial renderer offers two types of materials, one of which can be used to simulate hard surfaces such as glass, plastic, stainless steel and so on, because of the low difficulty of implementation and the early development of the basic materials, they have become more and more mature. The special material with subsurface scattering such as skin has been an important factor to evaluate the quality of a realistic renderer because of its high implementation difficulty and late development. On the other hand, because all non-conducting organisms have subsurface scattering properties, this material is widely used in film, television and games. Due to the slow convergence rate of the subsurface scattering material simulated by pure physics, it can not be applied in practice, and then the subsurface scattering material which is similar to the simulated subsurface scattering material emerges as the times require. However, these approximate methods have their own advantages and disadvantages. Some of them have fast rendering speed but generally complex process effects, while some simple process effects are first class but rendering speed is relatively slow. However, there are few researches on real-time subsurface scattering at present. The method proposed by Xu Kun can only be applied to the case where the illumination environment of an object is invariant. In this paper, two different subsurface scattering algorithms are studied in depth, and how to realize the subsurface scattering material under the renderman standard renderer is studied deeply, and a complete set of implementation is given. The experimental results are compared and analyzed. Then, a real-time subsurface scattering algorithm based on GPU is proposed, which is divided into two steps. In the first step, the texture coordinates of each coloring point are obtained by using the importance sampling method of BSSRDF. They are stored in the map. In the second step, when each coloring point is calculated, the coloring point color is obtained by merging the direct illumination of the object surface according to the texture coordinates obtained from the previous step. The main work of this paper is: 1. The fast hierarchical surface scattering based on point cloud is studied. The distribution of point cloud in REYES architecture renderer is optimized, and the multi-layer surface scattering algorithm is combined. In this paper, a fast hierarchical surface scattering algorithm with surface roughness is proposed, which can simulate smooth jade. A method is proposed to realize the subsurface scattering algorithm based on BSSRDF importance sampling in renderman renderer. In this paper, a simple and efficient BVH tree construction method is proposed for the intersection of light and scene. By improving the intersection algorithm of ray and quadrilateral in the previous renderer, a real-time subsurface scattering algorithm based on GPU is proposed by pre-calculating the important sampling points of BSSRDF and storing them into the map. For the first time, the method allows the illumination of objects to change in real time.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TP391.41
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