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面向双眼皮虚拟手术的三维网格编辑技术研究
管桐
学位类型工学硕士
导师叶军涛
2017-11
学位授予单位中国科学院研究生院
学位授予地点北京
关键词虚拟手术 几何特征 手术轨迹预测 网格编辑 光照效果
摘要双眼皮手术是整形美容手术中出现频率最高的一类手术,尤其在亚洲人群中广受欢迎。由于手术的不可逆性,如果能预先看到术后效果,无论对客户还是对医生都是福音。因此手术模拟系统以及虚拟手术系统是虚拟现实领域的一个研究热点。双眼皮手术模拟的技术难点主要集中在以下几个方面:如何用快速、简单、有效的手术轨迹预测取代繁琐的人机交互操作;如何在三角网格上进行细节信息不变的网格编辑;如何利用网格凹陷、褶皱程度去逼真地模拟手术区域的光照效果。本论文针对上述问题进行了探讨和研究,主要内容如下:
• 基于眼部几何特征的手术轨迹半自动生成。对于单眼皮的人眼来说,上眼睑轮廓线的形状和走向是双眼皮手术轨迹线的重要参考。为了自动提取上眼睑轮廓线,我们借助谷脊线等几何特征信息形成一条连续的曲线,然后根据这条曲线对网格曲面做相应变形,再针对变形后的曲面计算源点和目标点间的测地线,将曲面形状恢复后该测地线就是预测的手术轨迹线。有时受三维采集设备精度所限,网格的几何特征信息可能会有较大误差,为此我们还提出了一种基于人脸二维图像特征点预测手术轨迹的方法。在二维图像上提取关键特征点被投影到三维模型后,将相应的三维坐标点串联生成手术轨迹。
• 提出了一种自动生成术后疤痕效果的网格编辑方案。该方案对手术轨迹线穿过的三角面片进行自适应细分,从而保证凹陷网格曲面的平滑性。此外还提出了模拟手术疤痕宽度的近似等距线的计算方案。借助于近似等距线,可以扩宽双眼皮的宽度,同时保证临近顶点和面片的几何信息不受手术区域网格编辑操作的影响。
• 提出了一种模拟双眼皮光照效果的方法。在光照条件与模型材质不变的情况下,亮度值是只与光线入射角有关的函数,因此可以根据凹陷操作前后法向量夹角余弦值来计算某点的光亮度值,并据此对变形曲面网格进行明暗处理。此外,通过光强度线性插值法来绘制模型表面,从而保证了在曲面绘制中光强度的连续性。
 
相比于目前的虚拟手术模拟系统,本文提出的方案具有以下优势:(1)实现了手术轨迹预测流程的半自动化,消除了对繁琐人机交互的依赖;(2)对网格进行编辑时保持了局部细节特征不变;(3)逼真地模拟了双眼皮的光照效果。
其他摘要Double-eyelid surgery is one of the most popular plastic and cosmetic surgeries, especially among Asians. Due to the irreversibility of surgery, a preview of the post-surgery effect is instructive for both the customer and surgeon. Therefore, surgical simulation and virtual surgery system have attracted much interests in the virtual reality and computer graphics communities. The main technical difficulties of double-eyelid surgery simulation lie in the following aspects: how to replace the tedious human-machine interactions with fast, simple and effective surgery trajectory prediction; how to achieve detail-preserving mesh editing; how to simulate the illumination effects of the surgical area according to the remeshed surface and the wrinkle of the eyelid fold? This thesis has the following main contributions:
Semi - automatic generation of surgical trajectory based on eye geometry. For an eye with single-layered eyelid, the shape and direction of the upper eyelid contour line is an important reference for double-eyelid surgical trajectory. To extract the upper eyelid contour line automatically, we form a continuous curve based on the valley and ridge line as well as other geometric characteristics. Then we conduct mesh deformation according to this curve and calculate the geodesic line connecting the source point and the target point on the deformed surface. Once the surface shape restored, the geodesic is the predicted surgical trajectory. When a face mesh suffers from noises due to the limited accuracy of the 3D acquisition equipment, geometric feature extracted could be inaccurate. We propose another surgical trajectory prediction method using feature points of 2D face images. Specifically, we firstly extract feature points on a 2D face image, then project them onto the 3D face mesh. Connecting the corresponding 3D coordinate points, we can obtain a surgical trajectory prediction.
A mesh editing scheme for automatic generation of surgical scar effect. This scheme adaptively subdivides triangular faces through which the surgical trajectory passes. In addition, we propose a method for calculating approximately equidistant lines which can simulate the surgical scar width. Based on the approximately equidistant lines, we can widen the double-eyelid and ensure that the regions outside of the scar are not affected during the editing.
  Illumination effects simulation of double-eyelid. Under the same illumination condition and with the same material, the brightness is only a function of the incident angle of light. Therefore, we can calculate the brightness of a point according to the cosine value of the normal vector angle between the original grid and the new mesh, and mesh shading on the deformed mesh surface can be re-calculated. Additionally, we use linear interpolation to achieve smooth surface rendering.
  Compared with existing virtual surgery simulation systems, the proposed scheme has the following advantages: (1) semi-automatic prediction of the surgical trajectory, thus tedious human-computer interactions are avoided; (2) when editing a meh, the local detail features are preserved; (3) realistic illumination effects of double-eyelid.
学科领域计算机应用技术
文献类型学位论文
条目标识符http://ir.ia.ac.cn/handle/173211/15660
专题毕业生_硕士学位论文
作者单位中国科学院自动化研究所
推荐引用方式
GB/T 7714
管桐. 面向双眼皮虚拟手术的三维网格编辑技术研究[D]. 北京. 中国科学院研究生院,2017.
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