共查询到20条相似文献，搜索用时 15 毫秒
1.
Photorealistic visualization combines 3-D geometric models with their texture images to render the virtual world. This paper points out that the texture images should be radiometrically corrected to achieve a true realistic appearance. Such a correction should include not only the color adjustment among images of the same object, but also the shade variation caused by the illumination change. The objective of this study is to correct the input texture images such that their shade varies when being rendered under different illumination directions. To achieve this goal we first apply the specular-to-diffuse mechanism based on the dichromatic reflection model to remove the specular component from the texture image. The resultant diffusion-only image then undergoes a shade correction to produce a normalized shade-free texture image. In the final step, shades under any illumination are produced to achieve a true photorealistic effect. Presented in the paper are the principles and methods for such corrections, along with a performance evaluation based on the graphic and numerical results for roof texture images. 相似文献
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城市三维可视化中规则房屋墙面纹理图像的压缩与恢复 总被引：2，自引：1，他引：2
以城市三维可视化中的房屋墙面纹理图像为对象，就其压缩与恢复的方法进行了研究，提出了一种基于自相似性墙面纹理分割的纹理图像压缩与恢复方法，以及对由于遮挡而墙面不完整的纹理图像的复原方法，并通过实例说明了此种方法对于城市三维可视墙面纹理贴图的实用性。 相似文献
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几种小波基在遥感图像压缩中的应用效果比较 总被引：4，自引：0，他引：4
分析了小波基的基本性质,简述了在遥感图像小波压缩中小波基选择的常用方法; 分别用4种常用的典型小波基对8幅含有
不同典型地物的遥感图像进行小波编码实验,并用5种方法全面评价了小波基的应用效果。结果表明,在遥感图像小波压缩中,D
(9,7)小波基的应用效果最好。据此,提出了一种小波基选择的改进方法。 相似文献
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Vipula Singh Navin Rajpal K. Srikanta Murthy 《Journal of the Indian Society of Remote Sensing》2009,37(2):185-199
Image compression forms the backbone for several applications such as storage of images in a database, picture archiving,
TV and facsimile transmission, and video conferencing. Compression of images involves taking advantage of the redundancy in
the data present within an image. This work evaluates the performance of an image compression system based on fuzzy vector
quantization, wavelet-based sub band decomposition and neural network. The vector quantization is often used when high compression
ratios are required. The implementation consists of three steps: first, the image is decomposed into a set of sub bands with
different resolutions corresponding to different frequency bands. Different quantization and coding schemes are used for different
sub bands based on their statistical properties. In the second step, wavelet coefficients corresponding to the lowest frequency
band are compressed by differential pulse code modulation (DPCM) and the coefficients corresponding to higher frequency bands
are compressed using neural network. Finally, the result of the second step was used as input to fuzzy vector quantizer. Image
quality was compared objectively using mean squared error and peak signal to noise ratio along with the visual appearance.
The simulation results show clear performance improvement with respect to decoded picture quality when compared with other
image compression techniques (Liu, 2005; Premaraju, 1996). 相似文献
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常规激光点云数据通过将激光点云与彩色影像进行融合,将影像所富含的色彩信息赋给相应的激光点云、可形成一种"纹理丰富、颜色直观、位置准确"的真彩色点云成果,不同类型相机拍摄得到的影像对激光点云赋彩色的原理和过程均不相同。文中基于移动测量系统及360°全景影像的测绘高新技术,研究全景相机拍摄的影像与激光点云的匹配、融合,提出一种基于共线原理的由全景影像给激光点云赋彩色的算法。算法充分利用全景影像360°可视以及激光点云位置精确的特点,经实验验证算法推导正确,生成的真彩色点云色彩纹理细致,空间位置准确。 相似文献
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ZHANG Xubing YU Xin 《测绘科技情报》2008,(1)
针对MODIS(Moderate Resolution Imaging Spectroradiometer)影像数据海量并具有重要研究价值的特点,研究MODIS影像的无损压缩算法。采用最佳线性预测方法,通过波段相关性排序确定波段最优预测顺序,并自适应计算"预测波段"与"当前波段"的二阶最佳预测器系数,减少谱间冗余;以多级树集合分裂树(Set Partitioning In Hierarchical Trees,SPIHT)编码算法降低谱内相关。为确保无损压缩,对线性预测系数进行最佳逼近取整操作,并采用基于提升格式的D5/3整数小波变换。实验结果表明本文提出的算法在压缩比上性能较3DSPIHT等算法突出。 相似文献
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针对卫星云图数据量大,但传输通道和存储空间相对狭小的问题,本文基于Tetrolet变换,利用相邻时次云图的时空相关性,实现了一种高重构质量的卫星云图压缩感知方法。该方法将善于表达图像方向纹理及边缘信息的Tetrolet变换引入压缩感知的稀疏表示环节,从而很好地体现了卫星云图细节丰富、纹理结构复杂的特性;同时,考虑到卫星云图序列间的相关性,将时间相邻的卫星云图组成图像组,以中间时刻云图作为参考图像,计算其与相邻时次云图的差异,通过在参考图片及序列差异图片间合理分配采样率,获取测量数据,在压缩感知框架下,采用带平滑处理的投影Landweber算法,重构出相邻时次的图像组。实验结果表明,Tetrolet变换适用于卫星云图的稀疏表示,而且图像组时空相关性的利用可显著提高重构云图的视觉效果及客观评价指标;在采样率低于0.2时,红外1、水汽和可见光3个通道重构云图的峰值信噪比(PSNR)较传统方法平均提高了7.48 dB,13.51 dB和6.15 dB。由此可见,本文方法可以通过获取少数随机测量值,重构出高质量的卫星云图,不仅为云图数据的低比特率压缩提供了一种可行的解决方案,而且对于其他序列图像的压缩采样具有借鉴意义。 相似文献
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纹理是影响三维模型真实感的一个重要因素。三维纹理映射的最终目的是得到高精度、全自动、高保真的三维模型,它是计算机视觉等领域的一个热点问题。本文介绍了三维纹理映射的原理和过程;针对三维建筑模型进行纹理映射这一研究方向,在投影变换中参数化应用、纹理坐标转换的处理、影像与模型的匹配等方面总结现有的解决方法,并针对多幅建筑物立面的倾斜影像及屋顶垂直遥感影像与三维几何模型的纹理映射,将一些有代表性的研究方法和成果进行对比分析;最后根据当前的研究现状和应用需求,提出一些问题和解决途径。 相似文献
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城区大比例尺影像三维景观重建 总被引：1，自引：0，他引：1
本文利用目标提取技术,根据近似点位进行房屋角点的自动定位,自动搜索同名点,然后建立一个尽可能多地包含房顶面的目标窗口,取代传统的以房角为中心的窗口进行房顶角点影像匹配,提高了房顶角点匹配的可靠性,实现了航空影像房屋三维数据的半自动量测。进而在地面与建筑物表面二维半不规则三角网和原始数字影像的基础上,实现了建筑物可见表面纹理的恢复,重建了城市真实三维景观。 相似文献
10.
建筑物的三维建模是城市三维建模和可视化的重要组成部分。本文提出一种基于点云数据与遥感图像的建筑物三维模型快速建模方法。首先,运用改进的RANSAC法从点云数据中提取建筑立面,根据立面区分平顶建筑与人字形屋顶建筑;在此基础上,进一步对建筑物的高度进行提取;之后,利用区域增长法从遥感图像中提取建筑物屋顶轮廓,利用形态学方法对提取出的轮廓进行规则化处理,并基于Freeman链码提取轮廓角点,得到规整的轮廓;最后,根据提取出的建筑高度属性对屋顶轮廓拉伸并进行纹理映射,实现对建筑物的三维重建。通过实例证明,提出的方法能快速、高效地实现建筑物三维模型的重建。 相似文献
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Three-dimensional (3D) reconstruction and texture mapping of buildings or other man-made objects are key aspects for 3D city landscapes. An effective coarse-to-fine approach for 3D building model generation and texture mapping based on digital photogrammetric techniques is proposed. Three video image sequences, two oblique views of building walls and one vertical view of building roofs, acquired by a digital video camera mounted on a helicopter, are used as input images. Lidar data and a coarse two-dimensional (2D) digital vector map used for car navigation are also used as information sources. Automatic aerial triangulation (AAT) suitable for a high overlap image sequence is used to give initial values of camera parameters of each image. To obtain accurate image lines, the correspondence between outlines of the building and their line features in the image sequences is determined with a coarse-to-fine strategy. A hybrid point/line bundle adjustment is used to ensure the stability and accuracy of reconstruction. Reconstructed buildings with fine textures superimposed on a digital elevation model (DEM) and ortho-image are realistically visualised. Experimental results show that the proposed approach of 3D city model generation has a promising future in many applications. 相似文献
12.
在考虑地形特征和视相关特点的基础上,采用了一种简单的四叉树剖分评价函数用于实时生成动态的多分辨率地形模型。在三维场景漫游中,采用多级缓冲机制实现了视点快速移动下场景数据的调度和绘制,同时提出了一种综合考虑帧率和细分评价函数的自适应LOD调度方法,并采用和地形调度相一致的方法进行多级纹理映射。最后开展了算法实现的编程工作,实现了基于以上简化技术的大规模三维地形的可视化。 相似文献
13.
古建筑保护是当下测绘领域的热点研究课题，非接触测量是克服传统方法数字化不足、容易造成"二次破坏"的有力举措。本文以哈尔滨红霞街99号外侨私邸为例，提出了一种将三维激光扫描技术和无人机航测技术相结合进行古建筑重建的研究方案。基于三维激光扫描仪和无人机获取的古建筑内外点云数据和影像数据，利用点云数据生成正射影像并绘制平、立、剖面图，创建三维模型，最后以实地量取的建筑物尺寸数据为参考分析得出图纸和模型误差。结果表明：利用三维激光点云联合无人机影像能够高效地进行建筑图纸恢复，创建高精度精细化的三维模型，为古建筑保护提供了一种全新的思路。 相似文献
14.
An Evaluation of Four Different Wavelet Decomposition Procedures for Spatial Feature Discrimination in Urban Areas 总被引：2，自引：0，他引：2
Texture or spatial arrangement of neighborhood objects and features plays an important role in the human visual system for pattern recognition and image classification. The traditional spectral–based image processing techniques have proven inadequate for urban land use and land cover mapping from images acquired by the current generation of fine–resolution satellites. This is because of the high frequency spatial arrangements or complex nature of urban features. There is a need for an effective algorithm to digitally classify urban land use and land cover categories using high–resolution image data. Recent studies using wavelet transforms for texture analysis have generally reported better accuracy. Based on a high–resolution ATLAS image, this study illustrates four different wavelet decomposition procedures – the standard, horizontal, vertical, and diagonal decompositions – for urban land use and land cover feature extraction with the use of 33×33 pixel samples. The standard decomposition approach was found to be the most efficient approach in urban texture analysis and classification. For comparison purposes and to better evaluate the accuracy of wavelet approaches in image classification, spatial autocorrelation techniques (Moran's I and Geary's C ) and the spatial co–occurrence matrix method were also examined. The results suggest that the wavelet transform approach is superior to all other approaches. 相似文献
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本文介绍了一种基于轮廓纹理分解的三维谱象数据压缩方法。根据成象光谱仪三维谱象数据的特点，首先用轮廓纹理方法将其中二维单色图象分解成一系列轮廓及其包围的纹理。由于成象光谱仪三维谱象数据是同一地面景物沿波长方向展开的一叠单色图象，同一地面景物反映在不同波长的单色图的轮廓相同，但纹理不同。只需对其中某一单色图的轮廓编码即可。而各单色图因波长变化而引起的纹理变化只需对相应的多项式系数编码即可。采用本文的方法对用我国自行研制的６４波段航空机载成象光谱仪在澳大利亚达尔文地区试飞获得的三维谱象数据实验，当纹理系数用零阶多项式表示时可获得３７９：１的压缩比。 相似文献
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随着GIS用户对地理信息可视化性能要求的不断提高,虚拟地理场景的景物实体建模方法成为VRGIS领域的热点问题之一。本文探讨了一种基于立体视觉的影像多视点建模方法,包括景物实体表面影像纹理的采集和重建。影像纹理采集方面,提出了根据景物实体形状和景物实体表面纹理分布特点分配采集点的纹理采集方法。影像纹理重建方面,根据多幅影像对应特征点创建采样点模型,最后与几何模型进行空间配准,创建景物实体模型。以一实例进行实验论证,实验结果表明,该建模方法能够有效的提高虚拟地理环境中模型的真实感。 相似文献
20.
Automatic change detection and geo-database updating in the urban environment are difficult tasks. There has been much research on detecting changes with satellite and aerial images, but studies have rarely been performed at the street level, which is complex in its 3D geometry. Contemporary geo-databases include 3D street-level objects, which demand frequent data updating. Terrestrial images provides rich texture information for change detection, but the change detection with terrestrial images from different epochs sometimes faces problems with illumination changes, perspective distortions and unreliable 3D geometry caused by the lack of performance of automatic image matchers, while mobile laser scanning (MLS) data acquired from different epochs provides accurate 3D geometry for change detection, but is very expensive for periodical acquisition. This paper proposes a new method for change detection at street level by using combination of MLS point clouds and terrestrial images: the accurate but expensive MLS data acquired from an early epoch serves as the reference, and terrestrial images or photogrammetric images captured from an image-based mobile mapping system (MMS) at a later epoch are used to detect the geometrical changes between different epochs. The method will automatically mark the possible changes in each view, which provides a cost-efficient method for frequent data updating. The methodology is divided into several steps. In the first step, the point clouds are recorded by the MLS system and processed, with data cleaned and classified by semi-automatic means. In the second step, terrestrial images or mobile mapping images at a later epoch are taken and registered to the point cloud, and then point clouds are projected on each image by a weighted window based z-buffering method for view dependent 2D triangulation. In the next step, stereo pairs of the terrestrial images are rectified and re-projected between each other to check the geometrical consistency between point clouds and stereo images. Finally, an over-segmentation based graph cut optimization is carried out, taking into account the color, depth and class information to compute the changed area in the image space. The proposed method is invariant to light changes, robust to small co-registration errors between images and point clouds, and can be applied straightforwardly to 3D polyhedral models. This method can be used for 3D street data updating, city infrastructure management and damage monitoring in complex urban scenes. 相似文献