应用薄膜干涉模型进行蝴蝶彩色效果物理绘制

针对当前蝴蝶彩色效果绘制方法的真实感问题,提出一种应用薄膜干涉模型的真实感绘制方法.首先根据蝴蝶表面脊突结构构造多层薄膜模型;然后利用多层薄膜干涉原理模拟光在薄膜内部的多次反射、透射形成的混合散射特性,其中,菲涅尔公式被引入以解释反射或透射波的幅值变化,微表面散射因子被创造性地引入来模拟蝴蝶粗糙表面的各向异性特性;最后通过全波长光谱建模增强干涉效果,在此基础上还将该算法与光线追踪渲染框架相结合,构建了可应用于光线追踪器的波动双向散射分布函数干涉模型,以精确地模拟光的幅值和相位变动.实验结果表明,该模型能够有效地绘制出较为逼真的蝴蝶彩色效果.     

散景效果的真实感绘制

针对现有方法绘制的散景效果真实感较差的问题,提出一种基于几何光学理论的散景效果真实感绘制方法.该方法以光线传播的折射定律为基础,利用序列光线追踪方法对相机镜头的光学成像特性进行精确建模;对相机镜头的内部结构进行精确模拟,包括孔径光阑和渐晕光阑,以绘制出由孔径形状和渐晕共同作用的散景效果;利用几何光学理论和序列光线追踪方法精确计算出出射光瞳的位置和大小,以辅助光线采样,提高光线追踪效率.绘制结果表明,利用该方法能够绘制出较为逼真的散景效果,正确模拟了孔径形状和渐晕对散景效果的影响,并具有较高的光线追踪效率.     

非真实感绘制技术研究现状与展望

非真实感绘制技术（non-photorealistic rendering, NPR）主要用于模拟艺术风格、表现艺术特质和传达用户情感等,是计算机图形学的重要组成部分,其研究对象逐渐丰富,研究方法不断创新。本文从基于图像建模的绘制方法、基于深度学习的绘制方法、中国特有艺术作品的数字化模拟、非真实感情感特征识别以及非真实感视频场景绘制等5个方面概述目前研究进展,然后从扩展非真实感研究对象、增强视频绘制帧间连贯性、提取艺术风格情感特征以及评价非真实感绘制结果等4个角度讨论需要进一步研究的问题。针对需要深入研究的问题,指出提高算法的通用性和绘制效率,以及提高深度学习网络的泛化性,有助于扩展研究对象,模拟艺术风格的多样性,同时减小视频场景的帧间跳变;对艺术风格作品具有的情感特征、内在机理特征进行模拟,有助于提高绘制结果与艺术风格图像的相似度;结合主观和客观评价模型,可以更准确地对绘制结果进行评价,同时有利于优化网络模型参数,提高绘制效率。非真实感绘制在计算机视觉、文化遗产保护等领域具有重要的应用前景,但其研究对象、绘制算法、绘制效率仍然存在很多亟待解决的问题,随着硬件设备的不断改进,综合运用学科交叉知识、扩展应用领域将进一步推动非真实感绘制技术的发展。     

镜头重影效果的真实感绘制

针对现有镜头重影效果绘制方法存在的光线追踪效率低和绘制效果差的问题,提出一种基于物理的真实感镜头重影效果绘制方法.该方法以精确的相机镜头模型为基础,首先计算镜头入射光瞳的位置和孔径,并利用入射光瞳进行初始光线采样来减少无效光线数量,提高光线追踪效率;其次采用确定序列光谱光线追踪方法绘制重影的色差,并考虑了孔径光阑形状、镜头镀膜以及镜头遮挡对镜头重影的影响;最后将镜头重影绘制与光线追踪绘制框架融合,构成镜头重影场景绘制的统一框架,并在三维场景中实现了镜头重影效果的绘制.实验结果表明,文中方法能够有效地模拟具有较强真实感的镜头重影效果.     

基于模拟退火算法的水彩画仿真

为了快速有效地进行水彩非真实感绘制,综合考虑了工具材质的物理特性和视觉特征,提出一种基于模拟退火算法的水彩画计算机仿真方法.通过定义颜料颗粒解、产生函数和冷却进度表,并且利用解空间的迭代计算模拟水彩动静态属性.为了增加绘制效果真实感,利用Ashikhmin纹理映射算法合成水彩纸的自然背景纹理,并修正和迁移了光学库伯卡-芒克模型以融合纹理基质和颜料涂层,仿真了水彩肌理性特征.实验结果表明了该方法的有效性.     

一种基于人眼视觉特性的视频质量评价算法

为了更好地提高视频编码效率与视频处理的性能,考虑人眼对不同内容的感知特性和掩蔽效应,以及时域人眼视觉特性,提出一种基于人眼视觉特性的视频客观质量评价算法.首先利用三维Sobel矩阵提取时空特性划分区域,并结合恰可察觉失真视觉阈值与绝对差值图来提取感兴趣区域;然后对感兴趣区域进行感知加权,并利用线性加权进行空间域融合;最后结合时域人眼视觉特性,利用低通函数模拟人眼的不对称感知,并通过最差情况加权策略得到视频序列客观质量评价值.在LIVE视频质量数据库上的实验结果表明,该质量评价算法具有较好的评价性能,更接近于主观测试结果.     

基于可控金字塔的立体图像质量评价方法

在分析和模拟人眼感知立体图像方式的基础上,提出了一种评价立体图像质量的方法。该方法结合人眼视觉特征和结构相似度算法对立体图像质量进行评价,利用可控金字塔模拟人眼视觉特性中的多通道效应,同时采用立体图像左右视图的特征点的匹配算法对立体图像的立体感进行评价。实验结果表明,该方法与主观评价结果基本一致,能够更好地反映立体图像质量及立体感。     

基于GPU实时的大范围海水模拟

为了模拟出具有实时性和真实感的大范围海水场景,提出了一种绘制的方法,该方法使用了存在于投影空间的海面网格模型。同时,为了使海浪模拟的真实感更强,也未采用以往基于Perlin噪音的产生海浪高度图的方法,而是采用了更复杂的基于统计模型与快速傅立叶变换(FFT)的波浪生成方法。其次通过立方体纹理实现了海水对天空盒的反射效果,并运用Phone光照模型实现了海浪的反射。此外充分地利用了GPU硬件的特性和ping pong绘制技巧。实验证明该方法能快速模拟出实时、逼真的海水的场景。     

真实感雨线绘制

雨线的真实感绘制极具挑战性.雨滴在下落过程中会发生快速的震荡,由于光线在其中的反射和折射而具有复杂的光学效果,在人眼和摄像机观察时会产生运动模糊形成雨线.提出一种基于Monte Carlo光线跟踪的方法用于绘制真实感雨线.通过预先对雨滴震荡周期内每个离散时间点的雨滴三角形网格建立加速结构,并利用雨滴运动包围盒与采样光线的相交计算,大大加速了光线与雨滴的相交测试;使用自适应采样技术避免了对图像中每个像素点都使用大的采样数,提高了采样效率,加速了图像的绘制.将本文方法集成于离线绘制器(PBRT)中,生成了具有真实感的雨线图像和雨景动画.实验结果表明,本文方法能真实地模拟雨滴的震荡和光线在雨滴中的多次反射和折射,并能在包含任意类型光源的场景中有效地绘制真实感雨线.     

基于物理的浑浊水体的光照模拟

水体的真实感光照模拟是计算机图形学中的重要研究内容.现有的研究偏重于清澈水体的光照模拟,无法直接用于浑浊水体,为此提出一种基于物理的浑浊水体的真实感光照模拟方法.首先基于物质对水体光学特性的影响对浑浊水体进行建模,并分别建立每一类物质的吸收和散射模型;然后根据光线在浑浊水体中的传播及其与不同物质颗粒的交互作用计算光能的衰减变化,并将其转换为RGB颜色系统进行真实感绘制.借助GPU强大的并行处理能力,该方法可以实现对不同浑浊水体的光照效果的实时绘制.     

Rendering realistic spectral bokeh due to lens stops and aberrations

Creating bokeh effect in synthesized images can improve photorealism and emphasize interesting subjects. Therefore, we present a novel method for rendering realistic bokeh effects, especially chromatic effects, which are absent for existing methods. This new method refers to two key techniques: an accurate dispersive lens model and an efficient spectral rendering scheme. This lens model is implemented based on optical data of real lenses and considers wavelength dependency of physical lenses by introducing a sequential dispersive ray tracing algorithm inside this model. This spectral rendering scheme is proposed to support rendering of lens dispersion and integration between this new model and bidirectional ray tracing. The rendering experiments demonstrate that our method is able to simulate realistic spectral bokeh effects caused by lens stops and aberrations, especially chromatic aberration, and feature high rendering efficiency.     

A new Maxwellian view display for trouble‐free accommodation

We studied a new display system that realizes a Maxwellian view. The system is composed of a base display and a fly‐eye lens with micro‐pinholes. This forms ray intersecting points of diameter of 0.8 mm at a viewing distance of 280 mm. It was confirmed that the new display system can extend the depth of field of the human eye system, where the observer sets the ray intersecting point at his pupil.     

Interactive Simulation of the Human Eye Depth of Field and Its Correction by Spectacle Lenses

This paper describes a fast rendering algorithm for verification of spectacle lens design. Our method simulates refraction corrections of astigmatism as well as myopia or presbyopia. Refraction and defocus are the main issues in the simulation. For refraction, our proposed method uses per-vertex basis ray tracing which warps the environment map and produces a real-time refracted image which is subjectively as good as ray tracing. Conventional defocus simulation was previously done by distribution ray tracing and a real-time solution was impossible. We introduce the concept of a blur field, which we use to displace every vertex according to its position. The blurring information is precomputed as a set of field values distributed to voxels which are formed by evenly subdividing the perspective projected space. The field values can be determined by tracing a wavefront from each voxel through the lens and the eye, and by evaluating the spread of light at the retina considering the best human accommodation effort. The blur field is stored as texture data and referred to by the vertex shader that displaces each vertex. With an interactive frame rate, blending the multiple rendering results produces a blurred image comparable to distribution ray tracing output.     

基于最优采样模式的自适应光线投射法

三维直接体显示算法是显示三维数据体的一种重要显示方法,已广泛应用在医学图象生成和科学可视化领域之中。光线投射法又是三维直接体显示算法中最基本的一种方法。然而由于光线投射法需要大量的计算而受到限制。该文从减少光线投射数目的角度出发,提出了一种基于最优采样模式的频率投射算法。它的优点是不仅可以利用人的简单的视觉模型和强大的傅立叶分析工具,而且在采样模式上也更能符合人类视觉特点,减少了假模式,从而使更多     

Using Wavefront Tracing for the Visualization and Optimization of Progressive Lenses

Progressive addition lenses are a relatively new approach to compensate for defects of the human visual system. While traditional spectacles use rotationally symmetric lenses, progressive lenses require the specification of free-form surfaces. This poses difficult problems for the optimal design and its visual evaluation.
This paper presents two new techniques for the visualization of optical systems and the optimization of progressive lenses. Both are based on the same wavefront tracing approach to accurately evaluate the refraction properties of complex optical systems.
We use the results of wavefront tracing for continuously re-focusing the eye during rendering. Together with distribution ray tracing, this yields high-quality images that accurately simulate the visual quality of an optical system. The design of progressive lenses is difficult due to the trade-off between the desired properties of the lens and unavoidable optical errors, such as astigmatism and distortions. We use wavefront tracing to derive an accurate error functional describing the desired properties and the optical error across a lens. Minimizing this error yields optimal free-form lens surfaces.
While the basic approach is much more general, in this paper, we describe its application to the particular problem of designing and evaluating progressive lenses and demonstrate the benefits of the new approach with several example images.     

Research of the human eye model with variable-focus liquid lens

The human eye optical model with variable-focus liquid lens based on Chinese human eye model is presented for the first time. The Varioptic Arctic 316 liquid lens is used as a substitute for the crystalline lens in the model. The dioptric power and the MTF of the human eye model with variable-focus liquid lens are analyzed theoretically. The result shows that the human eye model with the liquid lens under applied voltage of about 53 V can be used as an emmetropia model. This research work can provide a novel idea for suitable model for clinical regulation and control with Chinese eye.     

基于人眼状态的瞌睡识别算法

已有瞌睡识别算法多数基于机器学习或深度学习,没有考虑到人眼闭合状态序列与瞌睡之间的关系。针对上述问题,提出了一种基于人眼状态的瞌睡识别算法。首先,提出了人眼分割和面积计算模型,基于人脸68个特征点,根据人眼特征点构成的极大多边形分割出眼睛区域,并利用眼睛像素点的总数代表眼睛面积大小;其次,计算极大状态下的人眼面积,并利用关键帧挑选算法挑选出最能代表睁眼程度的4帧,根据这4帧的人眼面积与极大状态下的人眼面积计算睁眼阈值,从而构建眼睛闭合度得分模型来确定人眼闭合状态;最后,根据输入视频的人眼闭合得分序列,构建了基于连续多帧序列分析的瞌睡识别模型。在两个国际常用的打哈欠检测数据集（YawDD）和NTHU-DDD数据集上进行瞌睡状态识别,实验结果表明,所提算法在两个数据集上的识别准确率均在80%以上,尤其是在YawDD数据集上,识别准确率达到94%以上。该算法可应用于驾驶员驾驶状态检测、学习者课中状态分析等。