基于法矢调整的浮雕曲面粘贴算法

浮雕是一类将细节附着在平面或曲面背景上的复杂曲面,设计时其背景大多为平面,应用时根据需要将其粘贴在不同的三维产品表面上,这就是浮雕曲面的粘贴问题。将浮雕和目标物体均用三角网格模型表示,提取粘贴的区域作为目标曲面并将其参数化到一个平面上,建立浮雕附着的平面与目标曲面之间的关系,然后设计一种法矢调整算法使得浮雕在目标曲面上变形较小,最后将浮雕和目标曲面合成为一个完整的三角网格。所提算法不仅适合形状变化平缓、曲率小的目标曲面,对于曲率大的目标曲面也有较好的粘贴效果。     

细节保持的曲面浅浮雕算法

为保持曲面浮雕的细节特征,改善浮雕与背景曲面的过渡效果,提出一种细节保持的曲面浮雕算法.首先采用Canny算子在梯度域定位内外轮廓,获得连续的梯度域;其次提出非线性函数,并用其压缩梯度幅值实现形状压缩;再通过双边滤波算子来保持和增强浮雕细节;最终通过求解积分方程重建曲面浮雕.该算法将背景曲面作为积分方程的优化条件,使浮雕在轮廓处向曲面光滑过渡;在重建过程中利用Fourier变换的微分性质在频域实现方程的精确求解,无需设置迭代收敛条件;通过调整参数可方便地控制浮雕整体变化范围、细节锐化程度以及浮雕与背景曲面的过渡效果.实验结果表明,文中算法参数的几何意义直观,所得曲面浮雕细节清晰,边界过渡自然.     

结合深度图像和强度图像的人脸浅浮雕生成算法

针对单纯基于深度图像压缩方法生成的三维浮雕模型容易存在大量噪声,并且易丢失细节的问题,为了生成特征表达准确且具有艺术美感的人脸浅浮雕,提出一种基于三维深度图像和与之对应的二维强度图像的混合人脸浅浮雕的生成算法.首先对三维深度图像的高度场进行压缩生成浮雕基网格;然后提取二维强度图像的灰度信息、梯度信息和显著度信息,并基于显著度信息对基网格的高度场相应地叠加灰度和梯度信息,以保持脸部五官的细节;最后根据显著度信息使用Laplace算子对网格进行光顺处理,使脸部光滑.实验结果表明,与单纯使用基于深度图像压缩方法相比,文中算法生成的浅浮雕模型可以更好地保持五官的细节特征;与基于图像的浮雕生成方法相比,该算法避免了复杂交互操作,可以更好地保持人脸的整体轮廓和形状.     

基于laplacian坐标修正的(√3)细分法

根据原始网格对细分极限曲面的影响分析,提出了基于laplacian坐标修正的(√3)插值网格细分方法.通过插值出面片中心点的laplacian坐标,来对动态生成的中心点进行修正,达到保持原始网格细节的目的.在非封闭网格的边界面片细分方面,指出了原始(√3)细分法的不足,提出了一种新的边界统一细分模式,它可以很好地控制边界面片的增长,而且具有稳定性和易于操作性.实验结果表明,该方法不仅能够让原始网格的细节在极限曲面上得到表达,而且可以得到一个连续光滑的曲面网格.     

网格模型离散微分几何量估算及应用

为了更好地估算网格模型离散微分几何属性,构造出一个新的三阶局部拟合算子.将Razdan 和Bae的网格模型二阶局部拟合曲面进行推广至三阶拟合曲面,更加准确地估算网格顶点法向量和曲率值;接着定义网格顶点的测地主挠率,使用该三阶拟合曲面对其估算;将估算出的曲率和挠率值作为几何特征属性,构造三维网格模型灰度图,并应用在非真实感绘制中,获得较好的渲染效果.     

STL三角形网格模型曲面特征边的提取

针对STL网格模型曲面特征边识别困难的问题,提出一种基于边和面的特征边提取方法。首先遍历网格模型,自适应地获取二面角阈值并根据该阈值识别显性特征边;然后利用最小二乘法估算曲面上顶点的平均曲率,由此计算出三角形面片的近似曲率,并利用相邻三角形的曲率差值来判别其公共的隐性特征边是否为特征边,最后采用改进的断点处特征边提取算法形成完整的特征边界。实验结果表明该方法能够有效地提取STL网格模型曲面网格的特征边,具有很好的鲁棒性。     

采用贝塞尔曲面纹理合成模拟三维真实感鱼体

针对三维真实感鱼体模拟的必要性及其纹理细节表现困难的问题,提出一种简单高效的真实感鱼体模拟方法.首先,通过调整双三次贝塞尔曲面的控制顶点完成鱼体左侧的各部分建模,根据鱼体的对称特性,实现整个鱼体的快速准确建模;其次,为真实模拟鱼体纹理细节及消除纹理合成中容易出现的接缝现象,对鱼体纹理合成单元做无缝预处理并将其转换成法向图,保证合成后的鱼体纹理光滑连续且细节表示真实自然.最后,利用Bezier曲面的u、v参数进行网格划分,u、v方向和跨度取值决定网格的方向和大小,体现出网格上鱼体纹理合成的方向和渐变细节.实验结果表明,该方法能够生成逼真的鱼体,且可任意改变鱼体的色泽和特征.     

三维重建网格模型的缺陷孔洞识别与修复方法

针对三维重建网格模型经常出现异常缺失孔洞的问题,提出一种缺陷孔洞自动识别与孔洞区域细节特征保持的曲面修复方法。首先对缺失区域的上下文及轮廓曲线进行异常检测以判断是否为缺陷孔洞, 确认为缺陷孔洞后对孔洞周边的特征线进行检测与匹配构造孔洞区域的基曲面;之后引进一个无约束的三角剖分对基曲面进行三角化;最后利用网格的各向异性进行细化及形态调整,改善网格的拓扑结构和几何性质。实验结果表明,该方法能够有效地识别三角网格模型的缺陷孔洞区域并还原其细节特征。     

一种基于物理的实时细节保持变形算法

实时变形是计算机图形学研究的热点问题之一,复杂物体的实时变形至今仍未得到很好的解决.从物理变形方法和多分辨率网格编辑技术的优点出发,提出了一种适合于复杂弹性物体的实时变形算法.在预处理阶段,将原始精细网格模型进行简化以建立其基网格表示,基于基网格对模型的局部细节特征进行编码;在实时绘制阶段,在基网格上进行物理变形操作,并通过变形后的基网格和细节编码重构出变形后的精细网格.以上过程充分利用图形硬件的并行处理能力,利用像素处理器进行大部分计算操作.实验结果表明,该算法在变形过程中较好地保持了物体的局部特征,适合于表面细节复杂物体的实时变形应用.     

基于laplacian坐标修正的sqrt(3)细分法

根据原始网格对细分极限曲面的影响分析,提出了基于laplacian坐标修正的sqrt(3)插值网格细分方法。通过插值出面片中心点的laplacian坐标,来对动态生成的中心点进行修正,达到保持原始网格细节的目的。在非封闭网格的边界面片细分方面,指出了原始3细分法的不足,提出了一种新的边界统一细分模式,它可以很好地控制边界面片的增长,而且具有稳定性和易于操作性。实验结果表明,该方法不仅能够让原始网格的细节在极限曲面上得到表达,而且可以得到一个连续光滑的曲面网格。     

Real‐time Bas‐Relief Generation from Depth‐and‐Normal Maps on GPU

To design a bas‐relief from a 3D scene is an inherently interactive task in many scenarios. The user normally needs to get instant feedback to select a proper viewpoint. However, current methods are too slow to facilitate this interaction. This paper proposes a two‐scale bas‐relief modeling method, which is computationally efficient and easy to produce different styles of bas‐reliefs. The input 3D scene is first rendered into two textures, one recording the depth information and the other recording the normal information. The depth map is then compressed to produce a base surface with level‐of‐depth, and the normal map is used to extract local details with two different schemes. One scheme provides certain freedom to design bas‐reliefs with different visual appearances, and the other provides a control over the level of detail. Finally, the local feature details are added into the base surface to produce the final result. Our approach allows for real‐time computation due to its implementation on graphics hardware. Experiments with a wide range of 3D models and scenes show that our approach can effectively generate digital bas‐reliefs in real time.     

Preserving detailed features in digital bas-relief making

This paper presents a novel algorithm for digitally making bas-reliefs. The problem requires visibly retaining fine details present in original 3D objects while greatly compressing their depths to produce an almost planar result. Our approach performs compression on the gradient domain; gradients are first estimated from a height field representing the input scene. A new compression function based on arctangent is introduced to preserve desired details of reliefs, allowing accurate height adjustment via a data-dependent threshold. We explicitly consider how to preserve fine details present in the original objects, which is crucial for producing high-quality bas-reliefs. Laplacian coordinates are used to store detailed features before depth compression and then restore them afterwards. Laplacian sharpening is also used to emphasize detailed features in the relief itself. Prior to depth compression, we process the input height field to reduce gaps in height, and detect the outer silhouette which allows to compute the output relief relative to a planar background or other surface, by solving a Poisson equation. This combination of techniques allows our method to produce bas-reliefs with well-preserved details.     

High Reliefs from 3D Scenes

We present a method for synthesizing high reliefs, a sculpting technique that attaches 3D objects onto a 2D surface within a limited depth range. The main challenges are the preservation of distinct scene parts by preserving depth discontinuities, the fine details of the shape, and the overall continuity of the scene. Bas relief depth compression methods such as gradient compression and depth range compression are not applicable for high relief production. Instead, our method is based on differential coordinates to bring scene elements to the relief plane while preserving depth discontinuities and surface details of the scene. We select a user‐defined number of attenuation points within the scene, attenuate these points towards the relief plane and recompute the positions of all scene elements by preserving the differential coordinates. Finally, if the desired depth range is not achieved we apply a range compression. High relief synthesis is semi‐automatic and can be controlled by user‐defined parameters to adjust the depth range, as well as the placement of the scene elements with respect to the relief plane.     

基于3维模型的数字浮雕生成技术

目的 浮雕是雕塑艺术的一种,根据其空间结构和用途的不同分为高浮雕、浅浮雕和凹浮雕3类。随着数字化技术和3D打印技术的发展,数字化浮雕的生成技术已经成为近年来计算机图形学领域的研究热点之一,从3维模型生成浮雕以其真实自然的效果成为浮雕生成的主要方法之一。为了使即将进入该领域的学者尽快了解该方法的现状和发展趋势,本文对3种类型的浮雕生成技术进行了系统的综述。方法 介绍了3种类型的浮雕生成技术,着重比较分析了基于3维网格模型的数字浅浮雕生成过程中的关键技术,存在问题及解决方案。针对复杂3维网格模型在生成数字凹浮雕过程中存在的部分细节信息丢失、特征线类型体现形式不完善、线条与形体间的过渡尚未解决、生成浮雕效果不自然等具体问题,提出了适用于3维复杂网格模型生成数字凹浮雕的研究方案。同时,从角色动画序列出发,对最优浮雕的生成技术进行了探讨,探讨结合信息熵理论计算选择最佳动作及观察视角的场景,还原艺术家的创作过程,为适用于面向3维打印的用户浮雕产品定制服务提供了可行的解决方案。结果 基于3维模型的浮雕生成方法是生成数字浮雕的一种重要方法,如何通过压缩和细节保持相关算法得到效果自然的浮雕模型一直是研究者们研究的热点问题。结论 虽然由3维模型生成数字浮雕是一种行之有效的方法,但是仍存在细节信息丢失、线条过渡不自然、特征线类型不完善等几个值得继续研究的问题,另外一个值得研究的问题就是如何智能地从3维动画序列生成浮雕。     

Adaptive Bas‐relief Generation from 3D Object under Illumination

Bas‐relief is designed to provide 3D perception for the viewers under illumination. For the problem of bas‐relief generation from 3D object, most existing methods ignore the influence of illumination on bas‐relief appearance. In this paper, we propose a novel method that adaptively generate bas‐reliefs with respect to illumination conditions. Given a 3D object and its target appearance, our method finds an adaptive surface that preserves the appearance of the input. We validate our approach through a variety of applications. Experimental results indicate that the proposed approach is effective in producing bas‐reliefs with desired appearance under illumination.     

Relief extraction and editing

Bas-reliefs are widely used in the world around us, for example, on coinage, for branding products, and for sculptural decoration. Reverse engineering of reliefs–extracting existing reliefs from input surfaces–makes it possible to apply them to new items; relief editing tools allow modification of reverse-engineered reliefs. This paper presents a novel approach to relief extraction based on differential coordinates, which offers advantages of speed and precise extraction. It also gives the first method in the literature specifically designed for relief editing. The base surface is estimated using normal smoothing and Poisson reconstruction, allowing a relief (which may lie on a smooth or textured input surface) to be automatically extracted by height thresholding. We also provide a range of relief editing tools, also using differential coordinates, permitting both global transformations (translation, rotation, and scaling) of the whole relief, as well as local modifications to the relief. Our relief editing algorithm, unlike generic mesh editing algorithms, is specifically designed to preserve the geometric detail of the relief over the base surface. The effectiveness of our methods is demonstrated on various examples of real industrial interest.     

Region-based bas-relief generation from a single image

Bas-relief is an art form part way between sculpture and drawing. In this paper, we present an algorithm for generating a bas-relief from a single image, inspired by the process that artists use to create reliefs. We do not aim to recover exact depth values for objects in the image, which is a tricky computer vision problem, requiring assumptions that are rarely satisfied. Instead, we determine layers based on relative depth ordering of objects (and their parts) in the image, and use this information to construct surfaces in the 3D relief model. Feature lines are extracted and used to build a new region-based representation of the input image. During surface construction, a base surface is first generated; it is then augmented using both intensity and gradient information from the original image. To prevent depth errors arising due to augmentation, a feedback process is used to refine the output. Our experimental results show the generated bas-reliefs have smooth boundaries with appropriate height relationships, a key property of bas-reliefs created by artists. We demonstrate that our algorithm works well for a range of input images, including human faces, flowers and animals.     

A framework for digital sunken relief generation based on 3D geometric models

Sunken relief is a special art form of sculpture whereby the depicted shapes are sunk into a given surface. This is traditionally created by laboriously carving materials such as stone. Sunken reliefs often utilize the engraved lines or strokes to strengthen the impressions of a 3D presence and to highlight the features which otherwise are unrevealed. In other types of relief, smooth surfaces and their shadows convey such information in a coherent manner. Existing methods for relief generation are focused on forming a smooth surface with a shallow depth which provides the presence of 3D figures. Such methods unfortunately do not help the art form of sunken reliefs as they omit the presence of feature lines. We propose a framework to produce sunken reliefs from a known 3D geometry, which transforms the 3D objects into three layers of input to incorporate the contour lines seamlessly with the smooth surfaces. The three input layers take the advantages of the geometric information and the visual cues to assist the relief generation. We have modified the existing techniques of line drawings and relief generation, and then combine them organically for this particular purpose.     

实时交互的带浮雕纹理的三维模型构建方法

为了快速生成带浮雕纹理的三维模型,提出一种实时交互的浮雕纹理模型构建方法。方法分两步：第一步,将生成浮雕的源模型或图像转换为初始深度图,并进一步转换为梯度图,再通过梯度域的压缩、过滤,求解线性方程重建出整体连续的浮雕深度图;第二步,借助基于网格求交的浮雕纹理映射算法将浮雕深度图贴在目标模型表面,并通过移动、旋转、缩放等操作实时在目标模型三维空间上修改浮雕效果,最终重建目标模型网格,生成浮雕纹理模型。实验表明,所提方法可快速实现在一个目标模型上生成凹浮雕、凸浮雕、多浮雕等效果,所得模型无需经过其他处理,可直接应用于3D打印,打印效果较好。