共查询到20条相似文献,搜索用时 218 毫秒
1.
2.
环境光遮蔽(ambient occlusion)被广泛用于近似计算低频全局光照、消除间接光照和阴影等计算机图形学和视觉应用中.已有算法直接通过场景的3维几何,或不同光照下的多幅图像计算每个点的环境光遮蔽,存在着对光照和输入图像数量要求高等问题.针对以上不足,提出了一种基于单张图像的环境光遮蔽估计算法.算法利用一个在大量仿真图像数据集上训练的卷积神经网络,直接从自然光照条件下场景的单张图像中恢复每个点的环境光遮蔽.提出并比较了3种不同的神经网络结构设计,实验分析验证了端到端的设计方案可以获得最佳的结果.和已有的环境光遮蔽算法方法比较,所提出的方法不仅计算速度快,而且在数值和视觉上具有更好的结果. 相似文献
3.
4.
变化光照的对象图像合成 总被引:3,自引:0,他引:3
光照是真实感图形绘制和许多图像应用中的一个非常重要的因素.提出了一种完全基于图像的方法来反映光照变化在绘制对图像时的影响.所提出的方法不是直接去估计对象反射模型中的参数,或是去拟合BRDF函数,而是用奇异值分解(SVD)来拟合Lambertian 对象在光照和几何朝向变化情况下的所有图像集合.其中,光线方向的解析表达可以由样本图像、基图像以及已知类对象的图像集导出,对象在新的光线方向下的图像可通过适当地线性组合基图像而有效地绘出.另外,利用对SVD系数的线性插值可以生成反映对象几何朝向和光线变化的连续变形 相似文献
5.
6.
廖新飞 《计算机工程与科学》2009,31(3)
基于图像的光照是计算机图形学中一个新的研究领域。本文研究了一种基于球面调和函数理论的快速光照技术,此方法采用三阶球面调和函数近似估计理想漫反射物体表面的光亮度,以此实现物体表面光亮度的计算。实验结果表明,本算法能够实现真实感图像的实时绘制。 相似文献
7.
8.
辐照度环境纹理图是绘制任意光照环境下漫反射物体表面的一种有效的方法。为了实现动态光照环境下辐照度环境纹理图的实时绘制,基于当前的通用图形硬件,提出了一种采用顶点着色器快速计算辐照度环境纹理图的方法。该方法从分析球面调和函数入手,首先得出环境贴图的二次多项式表达形式;然后用顶点着色程序对多项式系数和球面调和函数进行加速计算,以快速生成辐照度环境纹理图;最后对于动态光照环境,则通过对环境纹理图的分级细化来加快光照系数的计算,进而实现了动态光照环境下辐照度环境纹理图的重新绘制。实验表明,在动态光照条件下,采用该方法在获取真实感光照效果的同时,其运算速度也能满足交互系统的需求。 相似文献
9.
在介绍虚拟现实系统位置关联、时间关联、焦距关联和虚化关联的基础上,研究了基于图像的多关联性虚拟现实系统的设计。针对虚拟场景焦距关联的需要,在考虑场景真实性和实时性的基础上,采用基于熵变分分辨率增强和线性插值相结合的方法生成任意焦距下场景对应图像;对于时间关联,采用基于颜色传输的光照变化图像生成方法,实现不同光照条件下场景图像的生成;针对场景虚化关联的需要,结合非真实感绘制技术,采用真实感全景图像和波动感虚化特效图像相结合的方法,实现超越现实时空的场景虚化关联。在此基础上,给出了多关联性虚拟现实系统的构建框架。 相似文献
10.
针对带有微结构表面的几何模型全局光照计算复杂、难以达到实时性要求的问题,提出一种基于高度梯度图分析的全局光照实时绘制方法.首先,定义微结构高度梯度图,并据此构建可见点的局部最高点集合.其次,给出面向微结构表面对象实时绘制的全局光照计算模型,将光照计算近似分解为环境光入射、光源直接光照和一次交互漫反射这3种分量的计算.在环境光计算过程中,提出一种自适应环境光遮挡计算,借助局部最高点集合计算遮挡角.在直接光照中,给出一种微结构阴影的修正方法,搜索入射光方向的最近局部最高点剖面;通过比较剖面内光线投影与局部最高点的遮挡角,近似确定由微结构造成的阴影区域.最后,根据可见点的局部最高点集合确定一次交互漫反射的采样范围,进行渗色处理.整个全局光照计算方法在图像空间完成,较好地利用了延迟着色的思想和GPU并行计算的特点.算法可以在使用低精度几何模型时表现出带有微结构表面的高精度模型的全局光照效果,且适用于动态场景和可变形物体的全局光照计算. 相似文献
11.
基于图象的绘制(Image Based Rendering)作为一种全新的图形绘制方式,以其相对于传统几何绘制而言,具有高效实用的优点,近年来得到了研究人员越来越多的关注,但IBR技术仍存在一些主要难点,如图象的无缝拼接和实时漫游。针对此问题,开发了一个基于部分球面模型的室内虚拟漫游系统。该系统采用自动匹配和人机交互相结合的方法,可以无缝地将多幅照片拼接成一张全景图,同时采用一种改进的基于查找表的算法,实现了固定视点的实时漫游。 相似文献
12.
We present a method for rendering approximate soft shadows and diffuse indirect illumination in dynamic scenes. The proposed method approximates the original scene geometry with a set of tightly fitting spheres. In previous work, such spheres have been used to dynamically evaluate the visibility function to render soft shadows. In this paper, each sphere also acts as a low‐frequency secondary light source, thereby providing diffuse one‐bounce indirect illumination. The method is completely dynamic and proceeds in two passes: In a first pass, the light intensity distribution on each sphere is updated based on sample points on the corresponding object surface and converted into the spherical harmonics basis. In a second pass, this radiance information and the visibility are accumulated to shade final image pixels. The sphere approximation allows us to compute visibility and diffuse reflections of an object at interactive frame rates of over 20 fps for moderately complex scenes. 相似文献
13.
K. Vanhoey B. Sauvage O. Génevaux F. Larue J.‐M. Dischler 《Computer Graphics Forum》2013,32(6):101-112
Two‐dimensional (2D) parametric colour functions are widely used in Image‐Based Rendering and Image Relighting. They make it possible to express the colour of a point depending on a continuous directional parameter: the viewing or the incident light direction. Producing such functions from acquired data is promising but difficult. Indeed, an intensive acquisition process resulting in dense and uniform sampling is not always possible. Conversely, a simpler acquisition process results in sparse, scattered and noisy data on which parametric functions can hardly be fitted without introducing artefacts. Within this context, we present two contributions. The first one is a robust least‐squares‐based method for fitting 2D parametric colour functions on sparse and scattered data. Our method works for any amount and distribution of acquired data, as well as for any function expressed as a linear combination of basis functions. We tested our fitting for both image‐based rendering (surface light fields) and image relighting using polynomials and spherical harmonics. The second one is a statistical analysis to measure the robustness of any fitting method. This measure assesses a trade‐off between precision of the fitting and stability with respect to input sampling conditions. This analysis along with visual results confirm that our fitting method is robust and reduces reconstruction artefacts for poorly sampled data while preserving the precision for a dense and uniform sampling. 相似文献
14.
《Neural Networks, IEEE Transactions on》2009,20(12):1987-1993
15.
Guanyu Xing Xuehong Zhou Qunsheng Peng Yanli Liu Xueying Qin 《Computer Graphics Forum》2013,32(7):101-110
We propose a novel approach to simulate the illumination of augmented outdoor scene based on a legacy photograph. Unlike previous works which only take surface radiosity or lighting related prior information as the basis of illumination estimation, our method integrates both of these two items. By adopting spherical harmonics, we deduce a linear model with only six illumination parameters. The illumination of an outdoor scene is finally calculated by solving a linear least square problem with the color constraint of the sunlight and the skylight. A high quality environment map is then set up, leading to realistic rendering results. We also explore the problem of shadow casting between real and virtual objects without knowing the geometry of objects which cast shadows. An efficient method is proposed to project complex shadows (such as tree's shadows) on the ground of the real scene to the surface of the virtual object with texture mapping. Finally, we present an unified scheme for image composition of a real outdoor scene with virtual objects ensuring their illumination consistency and shadow consistency. Experiments demonstrate the effectiveness and flexibility of our method. 相似文献
16.
基于图像的光照模型研究综述 总被引:9,自引:1,他引:8
从传统图形学的绘制技术与基于图像的绘制技术相结合的角度出发,以全光函数这个基于图像的绘制技术的理论基础为核心,概括性地提出基于图像的光照研究的基本任务实际上是对全光函数的采样、重建、合成和重采样的过程,并进一步地指出,基于图像的光照研究的重要意义在于扩展了原有基于图像的绘制技术中只能改变视点位置和视线方向的限制,使之可以通过改变场景本身的组成成分产生出更加丰富的光照效果。同时,该文综述性地分析了近期内有关基于图像的光照问题的部分研究工作,并从如何改变场景光照条件的角度出发,按照所使用的光照模型的不同,将这些方法分成三大类,即利用传统光照模型的方法、利用基于图像的光照模型的方法以及无需光照模型的方法。并从这个分类框架出发,进一步分析指出,利用基于图像的光照模型的方法将是未来研究的重点,并沿着这一方向尝试性地提出了一种新的模型。 相似文献
17.
Jiaping Wang Kun Xu Kun Zhou Stephen Lin Shimin Hu Baining Guo 《The Visual computer》2006,22(9-11):713-720
In this paper, we present a new SH operation, called spherical harmonics scaling, to shrink or expand a spherical function in the frequency domain. We show that this problem can be elegantly formulated as a linear transformation of SH projections, which is efficient to compute and easy to implement on a GPU. Spherical harmonics scaling is particularly useful for extrapolating visibility and radiance functions at a sample point to points closer to or farther from an occluder or light source. With SH scaling, we present applications to low-frequency shadowing for general deformable object, and to efficient approximation of spherical irradiance functions within a mid-range illumination environment. 相似文献
18.
Ze Wang Chi-Sing Leung Yi-Sheng Zhu Tien-Tsin Wong 《Computer Vision and Image Understanding》2004,96(3):327
Image based relighting (IBL) solves the illumination control problem in the image-based modelling and rendering. However, it trades a drastic increase of storage requirement caused by the tremendous reference images pre-captured under various illumination conditions. In this paper, we propose a spherical wavelet transform and wavelet transform (SWT–WLT) based approach to compress the huge IBL dataset. Two major steps are involved. First, the spherical wavelet transform (SWT) is used to reduce the correlation between different reference images. Second, wavelet transform (WLT) is applied to compress those SW transformed images (SWT images). Due to the locality of SWT and WLT, the proposed method inherits an advantage of low memory requirement, hence, it is suitable for compressing arbitrarily large dataset. Using its integer format implementation this method can be further sped up with the help of bit shift operation. Simulations are given to evaluate its good features. 相似文献
19.
We present a novel technique for capturing spatially or temporally resolved light probe sequences, and using them for image
based lighting. For this purpose we have designed and built a real-time light probe, a catadioptric imaging system that can capture the full dynamic range of the lighting incident at each point in space at
video frame rates, while being moved through a scene. The real-time light probe uses a digital imaging system which we have
programmed to capture high quality, photometrically accurate color images of 512×512 pixels with a dynamic range of 10000000:1
at 25 frames per second.
By tracking the position and orientation of the light probe, it is possible to transform each light probe into a common frame
of reference in world coordinates, and map each point and direction in space along the path of motion to a particular frame
and pixel in the light probe sequence. We demonstrate our technique by rendering synthetic objects illuminated by complex
real world lighting, first by using traditional image based lighting methods and temporally varying light probe illumination,
and second an extension to handle spatially varying lighting conditions across large objects and object motion along an extended
path. 相似文献
20.
Face recognition from a single training image under arbitrary unknown lighting using spherical harmonics 总被引:1,自引:0,他引:1
Zhang L Samaras D 《IEEE transactions on pattern analysis and machine intelligence》2006,28(3):351-363
In this paper, we propose two novel methods for face recognition under arbitrary unknown lighting by using spherical harmonics illumination representation, which require only one training image per subject and no 3D shape information. Our methods are based on the result which demonstrated that the set of images of a convex Lambertian object obtained under a wide variety of lighting conditions can be approximated accurately by a low-dimensional linear subspace. We provide two methods to estimate the spherical harmonic basis images spanning this space from just one image. Our first method builds the statistical model based on a collection of 2D basis images. We demonstrate that, by using the learned statistics, we can estimate the spherical harmonic basis images from just one image taken under arbitrary illumination conditions if there is no pose variation. Compared to the first method, the second method builds the statistical models directly in 3D spaces by combining the spherical harmonic illumination representation and a 3D morphable model of human faces to recover basis images from images across both poses and illuminations. After estimating the basis images, we use the same recognition scheme for both methods: we recognize the face for which there exists a weighted combination of basis images that is the closest to the test face image. We provide a series of experiments that achieve high recognition rates, under a wide range of illumination conditions, including multiple sources of illumination. Our methods achieve comparable levels of accuracy with methods that have much more onerous training data requirements. Comparison of the two methods is also provided. 相似文献