共查询到19条相似文献,搜索用时 156 毫秒
1.
物体表面反射参数的恢复是新兴的逆向绘制技术的核心问题,提出一种恢复物体表面BRDF模型参数的方法,假定物体表面的BRDF模型可以近似分解为漫射纹理和整体不变的镜面反射分量,则每一点的反射参数可以用Phong模型来近似计算,首先选取物体表面的一片区域,利用该区域在不同视点光照条件下采样的几幅图像,计算得到该区域的平均镜面反射分量,作为整个物体表面的镜面反射分量,然后据此从物体表面各点的采样中分离出漫射分量,计算各点的漫反射参数,得到近似的BRDF模型,实验数据表明算法是有效的。 相似文献
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纺织品的真实感绘制是虚拟服装与试衣系统研究中的一项关键技术.采用图像图形结合的方法,提出了一种新的纺织品真实感绘制算法.对于场景中的实景,从原始照片中提取光照参数,将它与新纹理图相融合,利用色彩一致性理论和表面反射模型,达到类似于照片的展示效果.基于同样的理论研究,还可以模拟在纺织品的某些反射特性有所变化时的效果.对于原来场景中不存在的虚景,把用计算机生成的三维虚拟物体叠加到从真实世界获取的场景画面,应用实景提取的光照参数,并使用相应的光照模型对三维物体进行光照重计算.从而达到很好的虚实融合效果. 相似文献
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环境贴图是绘制物体表面漫反射和镜面反射效果的一种有效方法.为了把环境贴图应用于视景仿真中,实现场景对象的真实感绘制,首先从分析球面调和函数入手,提出了漫反射环境纹理图的快速计算方法;然后在研究镜面反射模型时,提出采用箱式滤波器代替Phong余弦函数滤波的方法,从而简化了镜面反射环境纹理图的滤波计算;最后在实现阶段,采用立方体环境纹理图表示场景光照环境,并对纹理图进行分级细化从而提高了绘制效率.实验表明,该方法在增强对象真实感的同时,其运算速度也能满足交互系统的需求,非常适合视景仿真应用. 相似文献
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现有的对半透明物体的绘制算法中大部分都是为均质材质设计的,虽然有少数算法可以绘制非均质材质,但效率不高,为此提出一种图形硬件加速的动态非均质半透明物体的实时绘制算法.首先将模型的采样点组织成八叉树的形式,将双向次表面散射反射函数(BSSRDF)表达绑定为顶点属性,同时充分利用图形硬件的并行性来实现八叉树的快速建立和遍历;然后以树的结点之间的空间距离和材质的相似度为准则提出一种新的采样方法来提高表面积分的效率.由于整个过程不需要任何预计算,因此该算法可以很容易地扩展到动画场景或者变化的材质,并且还可以灵活地选择BSSRDF的表达方式.实验结果表明,文中算法可以达到实时的绘制帧率和良好的视觉效果. 相似文献
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利用光强的可叠加性,本文提出了将光场分解为不随场景变化的子光场的思想,使得物体、光源、观察点都可自由变动的动态场景绘制也能利用基于图象的绘制技术之优势。依靠漫反射与观察方向的无关性,本文还提出了漫反射光场的四维表示法,并且利用物体对不同点光源的漫反射之间以及环境光与漫反射光之间的内在联系,只用一个单位强度的单色点光源为物体构造漫反射光场,从而节省了存储空间和预处理时间。利用其数据结构的一致性,环境光场、漫反射光场和深度场中对应点的数据被合并成5维矢量以便更有效地压缩。本文给出的绘制算法,能准确地计算出物体的颜色和场景中阴影的变化等动态场景的典型特征,从而为在低档计算机实现动态场景的实时绘制提供了理论和技术依据。 相似文献
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为了把环境贴图应用于VR系统中,实现场景对象的真实感绘制,首先从分析球面调和函数入手,提出了漫反射环境纹理图的快速计算方法。在研究镜面反射模型时,提出采用箱式滤波器代替Phong余弦函数滤波的方法,从而简化了镜面反射环境纹理图的滤波计算。在实现阶段,采用立方体环境纹理图表示场景光照环境,并对纹理图进行分级细化从而提高了绘制效率。实验表明,该方法实现了物体漫反射和镜面反射的快速绘制,非常适合虚拟现实应用。 相似文献
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现有的基于预计算的全局光照明绘制算法都假设场景中物体的材质固定不变,这样,从入射光照到出射的辐射亮度之间的传输变换就是线性变换.通过对这种线性变换的预计算,可以在动态光源下实现全局光照明的实时绘制.但是,当材质可以改变时,这种线性变换不再成立,因此,现有算法无法直接用于动态材质的场景.提出了一种方法:在修改场景中的物体材质时,可以实时得到场景在直接光照和间接光照下的绘制效果.将最终到达视点的辐射亮度根据其之前经过的反射次数及相应的反射材质分为多个部分,每个部分和先后反射的材质的乘积成正比,从而把该非线性问题转化为线性问题.又将所有可选的材质都表示为一组基的线性组合.将这组基作为材质赋予场景中的物体,就有各种不同的组合方式,预计算每种组合下所有部分的出射辐射亮度.在绘制时,根据各物体材质投影到基上的系数线性组合预计算的数据就能实时得到最终的全局光照明的绘制结果.该方法适用于几何场景、光照和视点都不发生变化的场景.使用双向反射分布函数来表示物体的材质,不考虑折射或者半透明的情况.该实现最多包含两次反射,并可以实时绘制得到一些很有趣的全局光照明效果,比如渗色、焦散等等. 相似文献
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一种用于动态场景的全景表示方法 总被引:3,自引:0,他引:3
针对全景图无法表示动态场景这一问题,提出一种用于动态场景的全景图表示方法,将视频纹理和全景图结合起来,构造动态全景图。系统首先将一系列定点拍摄的图像拼接成全景图,然后用摄像机拍摄场景中周期或随机运动的物体,提取视频纹理,最后视频纹理与全景图对准并融合,生成动态全景图。动态全景图既保持静态全景图全视角漫游的优点,又使得场景具有动态的特征,极大地增强漫游的真实感。 相似文献
11.
Rami R. Hagege 《Machine Vision and Applications》2014,25(5):1241-1256
The appearance of a static scene as sensed by a camera changes considerably as a result of changes in the illumination that falls upon it. Scene appearance modeling is thus necessary for understanding which changes in the appearance of a scene are the result of illumination changes. For any camera, the appearance of the scene is a function of the illumination sources in the scene, the three-dimensional configuration of the objects in the scene and the reflectance properties of all the surfaces in the scene. A scene appearance model is described here as a function of the behavior of static illumination sources, within or beyond the scene, and arbitrary three-dimensional configurations of patches and their reflectance distributions. Based on the suggested model, a spatial prediction technique was developed to predict the appearance of the scene, given a few measurements within it. The scene appearance model and the prediction technique were developed analytically and tested empirically. Two potential applications are briefly explored. 相似文献
12.
Rui Zhang Fan Zhong Lili Lin Guanyu Xing Qunsheng Peng Xueying Qin 《The Visual computer》2013,29(11):1197-1210
In augmented reality, it is essential that the rendered virtual objects are embedded harmonically into the view of the background scenes and their appearance should reflect the changing lighting condition of the real scene to ensure illumination consistency. In this paper, we propose a novel method to solve for the sunlight and skylight basis images of static outdoor scenes from a time-lapse image sequence. It is proved that the resulted basis images encapsulate the geometry and material reflectivity of the scene, correspond to the global illumination effects of the outdoor scene under a unit intensity of the sunlight and skylight. Our method is fully automatic. Unlike previous methods, it gets rid of the constraints that the reflectance of all objects in scenes should be ideal diffuse, or the weather condition should be overcast or sunshine. During decomposition, we first detect shadowed pixels by analyzing the time-lapse curve of each pixel through k-means clustering, the basis images of sunlight and skylight are then solved by an iterative procedure with the decomposition equation. The basis images are further optimized by exploiting their constraints and priors. Experimental results demonstrate the effectiveness and flexibility of the proposed method. Our method can also be applied in image understanding and compressing. 相似文献
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Lambert's model for diffuse reflection is extensively used in computational vision. It is used explicitly by methods such as shape from shading and photometric stereo, and implicitly by methods such as binocular stereo and motion detection. For several real-world objects, the Lambertian model can prove to be a very inaccurate approximation to the diffuse component. While the brightness of a Lambertian surface is independent of viewing direction, the brightness of a rough diffuse surface increases as the viewer approaches the source direction. A comprehensive model is developed that predicts reflectance from rough diffuse surfaces. The model accounts for complex geometric and radiometric phenomena such as masking, shadowing, and interreflections between points on the surface. Experiments have been conducted on real samples, such as, plaster, clay, sand, and cloth. All these surfaces demonstrate significant deviation from Lambertian behavior. The reflectance measurements obtained are in strong agreement with the reflectance predicted by the proposed model. The paper is concluded with a discussion on the implications of these results for machine vision. 相似文献
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CHEN XiaoWu JIN Xin WANG Ke 《中国科学:信息科学(英文版)》2014,(9):54-67
Achieving convincing visual consistency between virtual objects and a real scene mainly relies on the lighting effects of virtual-real composition scenes. The problem becomes more challenging in lighting virtual objects in a single real image. Recently,scene understanding from a single image has made great progress. The estimated geometry,semantic labels and intrinsic components provide mostly coarse information,and are not accurate enough to re-render the whole scene. However,carefully integrating the estimated coarse information can lead to an estimate of the illumination parameters of the real scene. We present a novel method that uses the coarse information estimated by current scene understanding technology to estimate the parameters of a ray-based illumination model to light virtual objects in a real scene. Our key idea is to estimate the illumination via a sparse set of small 3D surfaces using normal and semantic constraints. The coarse shading image obtained by intrinsic image decomposition is considered as the irradiance of the selected small surfaces. The virtual objects are illuminated by the estimated illumination parameters. Experimental results show that our method can convincingly light virtual objects in a single real image,without any pre-recorded 3D geometry,reflectance,illumination acquisition equipment or imaging information of the image. 相似文献
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StOMP algorithm is well suited to large-scale underdetermined applications in sparse vector estimations. It can reduce computation complexity and has some attractive asymptotical statistical properties.However,the estimation speed is at the cost of accuracy violation. This paper suggests an improvement on the StOMP algorithm that is more efficient in finding a sparse solution to the large-scale underdetermined problems. Also,compared with StOMP,this modified algorithm can not only more accurately estimate parameters for the distribution of matched filter coefficients,but also improve estimation accuracy for the sparse vector itself. Theoretical success boundary is provided based on a large-system limit for approximate recovery of sparse vector by modified algorithm,which validates that the modified algorithm is more efficient than StOMP. Actual computations with simulated data show that without significant increment in computation time,the proposed algorithm can greatly improve the estimation accuracy. 相似文献
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The Dichromatic Reflection Model (DRM) introduced by Shafer in 1985 is surely the most referenced physics-based model of image formation. A preliminary analysis of this model derives in the conclusion that colour channels remain coupled by the reflectance of objects surface material. Taking this observation as a basis, this paper shows that this coupling manifests itself at the signal level in the form of a set of properties only satisfied in uniform reflectance areas. Such properties are deeply analysed and formalized throughout the paper, and, eventually, they are stated geometrically. As will be seen, a compatibility relationship stems from this geometric interpretation, which allows checking at a very low cost whether two pixels correspond to the same scene reflectance or not. Finally, an edge detector based on the use of the previous relationship is presented as an example of application. This edge detector inherits all the properties of the compatibility relationship: simplicity, low computational power requirements, sensor noise adaptivity and insensitivity to image intensity changes due to scene objects curvature. 相似文献
17.
Baribeau R. Rioux M. Godin G. 《IEEE transactions on pattern analysis and machine intelligence》1992,14(2):263-269
A system for simultaneously measuring the 3-D shape and color properties of objects is described. Range data are obtained by triangulation over large volumes of the scene, whereas color components are separated by means of a white laser. Details are given concerning the modeling and the calibration of the system for bidirectional reflectance-distribution functions measurements. A reflection model is used to interpret the data collected with the system in terms of the underlying physical properties of the target. These properties are the diffuse reflectance of the body material, the Fresnel reflectance of the air media interface, and the slope surface roughness of the interface. Experimental results are presented for the extraction of these parameters. By allowing the subtraction of highlights from color images and the compensation for surface orientation, spectral reflectance modeling can help to understand 3-D scenes. A practical example is given where a color and range image is processed to yield uniform regions according to material pigmentation 相似文献
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Hsu-Huai Chang Yu-Chi Lai Chin-Yuan Yao Kai-Lung Hua Yuzhen Niu Feng Liu 《The Visual computer》2014,30(3):327-340
This work proposes a new voxelization algorithm based on newly available GPU functionalities and designs several real-time applications to render complex lighting effects with the voxelization result. The voxelization algorithm can efficiently transform a highly complex scene in a surface-boundary representation into a set of voxels in one GPU pass using the geometry shader. Newly available 3D textures are used to directly record the surficial and volumetric properties of objects such as opaqueness, refraction, and transmittance. In the first, the usage of 3D textures can remove those strenuous efforts required to modify the encoding and decoding scheme when adjusting the voxel resolution. Second, surficial and volumetric properties recorded in 3D textures can be used to interactively compute and render more realistic lighting effects including the shadow of objects with complex occlusion and the refraction and transmittance of transparent objects. The shadow can be rendered with an absorption coefficient which is computed according to the number of surfaces drawing in each voxel during voxelization and used to compute the amount of light passing through partially occluded complex objects. The surface normal, transmittance coefficient and refraction index recorded in each voxel can be used to simulate the refraction and transmittance lighting effects of transparent objects using our multiple-surfaced refraction algorithm. Finally, the results demonstrate that our algorithm can transform a dynamic scene into a set of voxels and render complex lighting effects in real time without any pre-processing. 相似文献
19.
Reflectance from images: a model-based approach for human faces 总被引:1,自引:0,他引:1
Fuchs M Blanz V Lensch H Seidel HP 《IEEE transactions on visualization and computer graphics》2005,11(3):296-305
In this paper, we present an image-based framework that acquires the reflectance properties of a human face. A range scan of the face is not required. Based on a morphable face model, the system estimates the 3D shape and establishes point-to-point correspondence across images taken from different viewpoints and across different individuals' faces. This provides a common parameterization of all reconstructed surfaces that can be used to compare and transfer BRDF data between different faces. Shape estimation from images compensates deformations of the face during the measurement process, such as facial expressions. In the common parameterization, regions of homogeneous materials on the face surface can be defined a priori. We apply analytical BRDF models to express the reflectance properties of each region and we estimate their parameters in a least-squares fit from the image data. For each of the surface points, the diffuse component of the BRDF is locally refined, which provides high detail. We present results for multiple analytical BRDF models, rendered at novel orientations and lighting conditions. 相似文献