虚平面映射:深度图像内部视点的绘制技术

首先推导与归纳了图像三维变换中像素深度场的变换规律,同时提出了基于深度场和极线原则的像素可见性别方法,根据上述理论和方法,提出一种基于深度图像的建模与绘制(image-based modeling and rendering,简称IBMR)技术,称为虚平面映射.该技术可以基于图像空间内任意视点对场景进行绘制.绘制时,先在场景中根据视线建立若干虚拟平面,将源深度图像中的像素转换到虚平面上,然后通过对虚平面上像素的中间变换,将虚平面转换成平面纹理,再利用虚平面的相互拼接,将视点的成像以平面纹理映射的方式完成.新方法还能在深度图像内侧,基于当前视点快速获得该视点的全景图,从而实现视点的实时漫游.新方法视点运动空间大、存储需求小,且可以发挥图形硬件的纹理映射功能,并能表现物体表面的三维凹凸细节和成像视差效果,克服了此前类似算法的局限和不足.     

Texture evolution: 3D texture synthesis from single 2D growable texture pattern

An efficient model-independent 3D texture synthesis algorithm based on texture growing and texture turbulence is presented to create vivid 3D solid texture from a single 2D growable texture pattern. Given a 2D texture pattern of some growable material, our technique is able to create an anisotropic 3D volumetric texture cube to simulate the evolution of the material in 3D. An effective tiling scheme is designed to save computation and storage costs. Target objects are directly dipped into the synthesized 3D texture volume to generate creative, sculpture-like models that can be visualized with interactive speed. Our method is conceptually intuitive, computationally fast, and storage efficient compared with other solid texturing methods. As opposed to conventional 2D texture mapping work on polygonal surfaces, our approach is capable of decorating 3D point-rendering systems seamlessly. Furthermore, our combination of texture turbulence and texture growing techniques provides an attractive way to synthesize and tile natural 2D texture patterns, or generate simple but interesting motion textures.     

Resolution Independent NPR-Style 3D Line Textures

This work introduces a technique for interactive walk-throughs of non-photorealistically rendered (NPR) scenes using three-dimensional (3D) line primitives to define architectural features of the model, as well as indicate textural qualities. Line primitives are not typically used in this manner in favour of texture mapping techniques which can encapsulate a great deal of information in a single texture map, and take advantage of GPU optimizations for accelerated rendering. However, texture mapped images may not maintain the visual quality or aesthetic appeal that is possible when using 3D lines to simulate NPR scenes such as hand-drawn illustrations or architectural renderings. In addition, line textures can be modified interactively, for instance changing the sketchy quality of the lines. The technique introduced here extracts feature edges from a model, and using these edges, generates a reduced set of line textures which indicate material properties while maintaining interactive frame rates. A clipping algorithm is presented to enable 3D lines to reside only in the interior of the 3D model without exposing the underlying triangulated mesh. The resulting system produces interactive illustrations with high visual quality that are free from animation artifacts.     

地形仿真中遥感影像的应用及处理技术

在分析几种地球表面表示方法的优缺点的基础上,提出用遥感影像作为三维地形仿真中表面纹理图以提高真实感的思想;提出不同高度实体视景地形的仿真应采用多级精度仿真的方案,并分析了地形仿真精度与影像分辨率间的关系;详细叙述了该应用方案中影像数据处理的流程及方法,包括：数据准备、真彩波段组合、影像增强、几何校正、拼接镶嵌、投影变换及三维地形生成等。实践证明,合理的影像数据处理方法和步骤可减少工作量并保证影像处理的精度和效果,现势件好,真彩组合的遥感影像用作三维地形仿真的表面纹理图是提高仿真真实感的有效技术途径。     

Texture mapping and distortion in digital graphics

Texture mapping is a method commonly used to increase the visual complexity of computer generated images while maintaining simplicity in the underlying geometric models. Texture maps are generally defined in two dimensional space; thus, a primary problem when applying textures to objects is determining a mapping transformation from the three dimensional space of the object to the two dimensional space of the map. A method for mapping complex polygonal geometries is presented. The algorithmunfolds the object polygon by polygon and projects the texture map onto the resulting two dimensional geometry. Enhancements to the basic unfolding algorithm either (1) control the location of map distorition introduced at areas of severe curvature or (2) average distortions over a larger area.     

Volumetric Billboards

We introduce an image‐based representation, called volumetric billboards, allowing for the real‐time rendering of semi‐transparent and visually complex objects arbitrarily distributed in a 3D scene. Our representation offers full parallax effect from any viewing direction and improved anti‐aliasing of distant objects. It correctly handles transparency between multiple and possibly overlapping objects without requiring any primitive sorting. Furthermore, volumetric billboards can be easily integrated into common rasterization‐based renderers, which allows for their concurrent use with polygonal models and standard rendering techniques such as shadow‐mapping. The representation is based on volumetric images of the objects and on a dedicated real‐time volume rendering algorithm that takes advantage of the GPU geometry shader. Our examples demonstrate the applicability of the method in many cases including levels‐of‐detail representation for multiple intersecting complex objects, volumetric textures, animated objects and construction of high‐resolution objects by assembling instances of low‐resolution volumetric billboards.     

High-quality texture reconstruction from multiple scans

The creation of three-dimensional digital content by scanning real objects has become common practice in graphics applications for which visual quality is paramount, such as animation, e-commerce, and virtual museums. While a lot of attention has been devoted recently to the problem of accurately capturing the geometry of scanned objects, the acquisition of high-quality textures is equally important, but not as widely studied. In this paper, we focus on methods to construct accurate digital models of scanned objects by integrating high-quality texture and normal maps with geometric data. These methods are designed for use with inexpensive, electronic camera-based systems in which low-resolution range images and high-resolution intensity images are acquired. The resulting models are well-suited for interactive rendering on the latest-generation graphics hardware with support for bump mapping. Our contributions include new techniques for processing range, reflectance, and surface normal data, for image-based registration of scans, and for reconstructing high-quality textures for the output digital object     

High-Dynamic-Range Texture Compression for Rendering Systems of Different Capacities

In this paper, we propose a novel approach for high-dynamic-range (HDR) texture compression (TC) suitable for rendering systems of different capacities. Based on the previously proposed DHTC scheme, we first work out an improved joint-channel compression framework, which is robust and flexible enough to provide compressed HDR textures at different bit rates. Then, two compressed HDR texture formats based on the proposed framework are developed. The 8 bpp format is of near lossless visual quality, improving upon known state-of-the-art algorithms. And, to our knowledge, the 4 bpp format is the first workable 4 bpp solution with good quality. We also show that HDR textures in the proposed 4 bpp and 8 bpp formats can compose a layered architecture in the texture consumption pipeline, to significantly save the memory bandwidth and storage in real-time rendering. In addition, the 8 bpp format can also be used to handle traditional low dynamic range (LDR) RGBA textures. Our scheme exhibits a practical solution for compressing HDR textures at different rates and LDR textures with alpha maps.     

Texture-based visualization of unsteady 3D flow by real-time advection and volumetric illumination

This paper presents an interactive technique for the dense texture-based visualization of unsteady 3D flow, taking into account issues of computational efficiency and visual perception. High efficiency is achieved by a 3D graphics processing unit (GPU)-based texture advection mechanism that implements logical 3D grid structures by physical memory in the form of 2D textures. This approach results in fast read and write access to physical memory, independent of GPU architecture. Slice-based direct volume rendering is used for the final display. We investigate two alternative methods for the volumetric illumination of the result of texture advection: First, gradient-based illumination that employs a real-time computation of gradients, and, second, line-based lighting based on illumination in codimension 2. In addition to the Phong model, perception-guided rendering methods are considered, such as cool/warm shading, halo rendering, or color-based depth cueing. The problems of clutter and occlusion are addressed by supporting a volumetric importance function that enhances features of the flow and reduces visual complexity in less interesting regions. GPU implementation aspects, performance measurements, and a discussion of results are included to demonstrate our visualization approach.     

Layered textures for image-based rendering

An extension to texture mapping is given in this paper for improving the efficiency of image-based rendering. For a depth image with an orthogonal displacement at each pixel, it is decomposed by the displacement into a series of layered textures (LTs) with each one having the same displacement for all its texels. Meanwhile, some texels of the layered textures are interpolated for obtaining a continuous 3D approximation of the model represented in the depth image. Thus, the plane-to-plane texture mapping can be used to map these layered textures to produce novel views and the advantages can be obtained as follows: accelerating the rendering speed, supporting the 3D surface details and view motion parallax, and avoiding the expensive task of hole-filling in the rendering stage. Experimental results show the new method can produce high-quality images and run faster than many famous image-based rendering techniques.     

使用多重纹理实时绘制Phong高光表面

物体表面的高光现象均由镜面反射的一个复杂的非线性表达式描述,这为实时绘制带来了困难,由此本文提出了一种使用纹理映射技术绘制高光表面的方法。首先将具有镜面反射表达式的Phong模型分解成多个预计算的函数,然后存储为纹理图,最后使用多重纹理技术将这些纹理组合起来,实现高光表面的绘制。实验结果表明,本文算法大大提高了绘制的性能。     

Floating Textures

We present a novel multi‐view, projective texture mapping technique. While previous multi‐view texturing approaches lead to blurring and ghosting artefacts if 3D geometry and/or camera calibration are imprecise, we propose a texturing algorithm that warps (“floats”) projected textures during run‐time to preserve crisp, detailed texture appearance. Our GPU implementation achieves interactive to real‐time frame rates. The method is very generally applicable and can be used in combination with many image‐based rendering methods or projective texturing applications. By using Floating Textures in conjunction with, e.g., visual hull rendering, light field rendering, or free‐viewpoint video, improved rendering results are obtained from fewer input images, less accurately calibrated cameras, and coarser 3D geometry proxies.     

一个新的基于3D纹理映射及Shear-warp变换的快速体绘制方法

介绍了一个新的基于纹理映射及Shear-warp变换的快速体绘制方法。所提出的方法吸收了纹理映射方法的长处，通过纹理硬件的加速，并在纹理装载时提出了可适应性的纹理分割方法，使该算法不受纹理内存的限制。在进行纹理映射时，通过剪切（Shear）变换和三维图象的分割，加快给制速度。与多种经典的快速体绘制方法进行测试比较，该方法达到了交互的效果和更高的绘制速度。     

Geodesic-driven visual effects over complex surfaces

Texture mapping is an important technique for adding visual details to geometric models. Image-based texture mapping is the most popular approach, but it relies on pre-computed images which often limit their use to static effects. For adding dynamic effects, procedural-based texturing is more adequate. Since it rely on functions to describe texturing patterns, procedural texturing allows for a more compact representation and control of visual effects by a simple change of parameters. In this work we describe GeoTextures, an approach that uses geodesic distance fields defined from multiple sources at different locations over a model surface to place, advect, and combine procedural visual effects over complex surfaces. The use of geodesics extends the scope of common procedural textures which are usually limited to using spatial 3D coordinates or 2D texture coordinates. We illustrate the flexibility of our real-time approach with a range of visual effects, such as time-based propagation of weathering phenomena, transparency effects, and mesh displacement over surfaces with smooth silhouettes using hardware based tessellation available in current graphics cards.     

Visualization of Large‐Scale Urban Models through Multi‐Level Relief Impostors

In this paper, we present an efficient approach for the interactive rendering of large‐scale urban models, which can be integrated seamlessly with virtual globe applications. Our scheme fills the gap between standard approaches for distant views of digital terrains and the polygonal models required for close‐up views. Our work is oriented towards city models with real photographic textures of the building facades. At the heart of our approach is a multi‐resolution tree of the scene defining multi‐level relief impostors. Key ingredients of our approach include the pre‐computation of a small set of zenithal and oblique relief maps that capture the geometry and appearance of the buildings inside each node, a rendering algorithm combining relief mapping with projective texture mapping which uses only a small subset of the pre‐computed relief maps, and the use of wavelet compression to simulate two additional levels of the tree. Our scheme runs considerably faster than polygonal‐based approaches while producing images with higher quality than competing relief‐mapping techniques. We show both analytically and empirically that multi‐level relief impostors are suitable for interactive navigation through large urban models.     

A PC-based high-quality and interactive virtual endoscopy navigating system using 3D texture based volume rendering

As an alternative method to optical endoscopy, visual quality and interactivity are crucial for virtual endoscopy. One solution is to use the 3D texture map based volume rendering method that offers high rendering speed without reducing visual quality. However, it is difficult to apply the method to virtual endoscopy. First, 3D texture mapping requires a high-end graphic workstation. Second, texture memory limits reduce the frame-rate. Third, lack of shading reduces visual quality significantly. As 3D texture mapping has become available on personal computers recently, we developed an interactive navigation system using 3D texture mapping on a personal computer. We divided the volume data into small cubes and tested whether the cubes had meaningful data. Only the cubes that passed the test were loaded into the texture memory and rendered. With the amount of data to be rendered minimized, rendering speed increased remarkably. We also improved visual quality by implementing full Phong shading based on the iso-surface shading method without sacrificing interactivity. With the developed navigation system, 256 x 256 x 256 sized brain MRA data was interactively explored with good image quality.     

高质量的三维纹理硬件体绘制

与光线投射法相比,传统的3D纹理体绘制算法通常难以产生高质量的图像。为了增强渲染图像的真实感与质量,在基于GPU（Graphics Processing Unit）的三维纹理体绘制过程中以交互的速率实现了体阴影效果,并考虑现实图像合成中的可视化感知,提出将基于GPU的高动态范围色调映射技术应用到体绘制得到的结果图片中。最后对一些体数据集进行绘制,实验表明这些技术较好地解决了传统纹理绘制方法的缺点,提高了图像的质量。     

Anti-aliased and real-time rendering of scenes with light scattering effects

Recently, for real-time applications such as games, the rendering of scenes with light scattering effects in the presence of volumetric objects such as smoke, mist, etc., has gained much attention. Slice-based methods are well-known techniques for achieving fast rendering of these effects. However, for real-time applications, it is necessary to reduce the number of slice planes that are used. As a result, aliasing (striped patterns) can appear in the rendered images. In this paper, we propose a real-time rendering method for scenes containing volumetric objects that does not generate aliasing in the rendered images. When a scene consists of volumetric and polygonal objects, the proposed method also does not generate aliasing at the boundaries between the polygonal and the volumetric objects. Moreover, we are able to reduce aliasing at shadows inside a volumetric object that are cast by polygonal objects by interpolating the occlusion rates of light at several locations. The proposed method can be efficiently implemented on a GPU.     

纹理映射中的平面校正技术研究

为了快速实时地进行由平面组成的结构景物的3D建模问题,文中介绍了一种在进行图像3D重构时纹理映射中的平面校正方法。介绍了三角形模型在图像处理、图形绘制、虚拟现实等技术中的重要作用。从射影几何的角度出发,给出了从两幅视图进行景物三维重构的分层重构方法。在已知欧氏重构即摄像机内参数的基础上,介绍一种基于标定的平面射影失真矫正方法。通过此方法,将矫正过的纹理映射到欧式点重构结构中,得到景物的3D模型。经实验验证,这种方法在处理由平面组成的景物的3D重构中是实时有效的。     

真实感3D重建中的纹理映射技术

精确的纹理映射是体现模型视觉真实感的关键因素。本文在阐述纹理映射技术原理的基础上,探讨了基于3维激光扫描设备进行3D重建过程中,实现具有高度真实感的纹理映射所遇到的实际问题,提出了基于纹理的模型重构和纹理光照连续性重建算法,解决了纹理图像空间不连续、光照不连续等因素对模型真实感的影响,并通过真实数据的实验对算法有效性进行了验证,为大型户外实体的真实感3D重建奠定了技术基础。