Dividing Cubes算法生成的物体表面的法向量方向的光顺操作

Smoothing Operation of Normal Directions on Object Surface Produced by Dividing Cubes

在用 Dividing Cubes算法提取的边界体素所构造的物体表面上 ,可能会存在法向量方向突变 ,使得物体表面光照图显示粗糙 .文中提出了一种改进的邻域加权平均法 ,对物体表面的法向量方向进行光顺处理 ,光顺操作只在相关边界体素间进行 ,并且对有多个等值面交汇的边界体素将不进行光顺操作 ,以避免模糊位于多个区域处的边界和保持物体表面光照图的细节 .为避免在屏幕上产生孔洞 ,用光线投射法显示物体表面 .文中所采用的光顺操作可以消除物体表面的法向量方向突变 ,使物体表面光照图光滑细腻 .最后 ,给出一个医学图像的测试实例 .

There might exist abrupt changes of the normal directions on a voxel object surface generated by Dividing Cubes, which would cause the shading image of the object look coarse and rough. A modified neighborhood weighted average approach was proposed in this paper for smoothing the normal directions on the voxel object surface. To avoid blurring the boundaries among several regions and preserve the details of the shading image of the object surface, the smoothing operation was only applied to those boundary voxels which were relevant, while the boundary voxels which had several isosurfaces were not smoothed. The algorithm of Ray Casting was used to display the object surface to avoid producing missing holes on the screen. The modified approach can eliminate those abrupt changes of the normal directions on the voxel object surface and improve the display quality. A verified example of a medical volume data is presented.