基于实时主方向估计的素描渲染  

Advanced Real-Time Principal Direction Estimation and Sketch Rendering Based on It

作　　者：张严辞 龚昱宁[1] ZHANG Yanci;GONG Yuning(College of Software,Sichuan University,Chengdu 610207,China;National Key Laboratory of Fundamental Science on Synthetic Vision,Sichuan University,Chengdu 610065,China)

机构地区：[1]四川大学软件学院,成都610207 [2]四川大学视觉合成图形图像技术国家重点学科实验室,成都610065

出　　处：《重庆理工大学学报（自然科学）》2020年第9期217-229,共13页Journal of Chongqing University of Technology：Natural Science

基　　金：国家自然科学基金项目(61472261)。

摘　　要：提出了一种更具鲁棒性的实时主方向估计算法与一种高效率且透视正确的线卷积积分算法,并在此基础上提出了一种素描渲染算法,以解决现有素描渲染算法中渲染结果不够贴近手绘效果以及绘制出的线条的透视错误问题。该算法的核心是首先利用了几何缓冲构建焦平面来获取每个像素点的主方向,并通过对多组焦平面采样的结果进行回归来获得更具鲁棒性的结果,解决了传统主方向实时估计中的黑块问题。相比于需要大量时间且不能改变顶点间关系的预计算算法,能适用于顶点动画以及蒙皮网络。其次,提出了一种新的线卷积算法,使其能在连续的二维及三维空间进行卷积,解决了传统的线卷积中透视出错的问题,并利用有序抖动减少线卷积积分所需的步数,提高了性能。最后结合手绘素描绘制的方式及其在效果表现上的侧重点,通过使用两个主方向夹角的角平分线作为线卷积积分的方向减少了画面的处理复杂度,并对渲染结果的一些细节进行调整,让渲染出的效果更加接近素描应有的效果。实验结果表明:所提出算法的实时主方向估计更具鲁棒性且能适用于复杂模型,且用于素描渲染的线卷积积分的效果以及性能均有提升。This paper proposes a more robust real-time principal direction estimation algorithm and also a highly efficient and projection-correct Line Integral Convolution(LIC)algorithm.Based on these two new algorithms,a new sketch rendering algorithm is proposed to solve the problems that the rendering result of traditional sketch rendering algorithm is not close enough to the hand-drawn results and the projection of the lines drawn by the algorithm is wrong.The core of the algorithm is,firstly using the G-Buffer to construct the focal plane to obtain the principal direction of each pixel,and then regressing the results of multiple sets of focal plane samplings to obtain more robust results.As a result,it solves the problem of"black blocks"of the traditional principal direction estimation algorithm.This algorithm is also more suitable for principal direction estimation of the vertex animation and skinning mesh which require a lot of time of pre-calculation and changing the relationship between vertices on the fly.Secondly,a new Line Integral Convolution algorithm is proposed,which makes the Line Integral Convolution not only projection-correct but also able to convolute in continuous two-dimensional and three-dimensional vector fields.Besides,via adapting ordered dithering,the number of steps required for convolution integration is reduced,which improves the performance of rendering.Finally,by analyzing the steps and points of focus of hand-drawn sketch,it is found that via using the angle bisector of the two principal directions as the direction of the Line Integral Convolution instead of directly using one of the principal directions,the processing complexity of the rendering results is reduced.Finally,we apply some adjustments to some details by post-processing,making the rendered result closer to the hand-drawn sketch.The experiments show that the real-time principal direction estimation algorithm in this paper is more robust and can be applied to complex models,and both the effect and performance of Line Integral Co

关 键 词：素描渲染 实时渲染 非真实感渲染 结构缓冲 有序抖动 

分 类 号：TP391.4[自动化与计算机技术—计算机应用技术]