基于纹理映射与Phong光照模型的体绘制加速算法

Accelerated Volume Rendering Using Texture Mapping with Phong Shading

为了提高体绘制速度,提出了一种基于纹理映射、具有Phong光照效果的体绘制加速算法.该算法是根据Phong光照模型,利用一单位球面体来仿真相同光照绘制条件下的每一个体素的反射光强,首先形成一个以法线矢量为索引值的反射光强查寻表,再应用窗值变换的加速算法来计算体素的不透明度;然后采用纹理映射的方法将体素光强值与由不透明度组成的3D数据集从物体空间投射到观察空间,再沿视方向融合为3D图象.实验表明,这种3D旋转的明暗修正保证了体绘制中3D旋转几何变换的多视角观察的交互速度.由于该算法综合了体绘制软件算法数据处理与纹理映射硬件加速的优点,并用2D纹理映射与融合的方法实现了体数据的3D重建,因而不仅降低了对计算机硬件与软件环境的要求,而且在目前通用个人计算机上即可获得近似实时的交互绘制速度和良好的3D图象品质.据研究,该算法同样适用于3D纹理映射的体绘制方法.

An accelerated algorithm of volume rendering with Phong shading based on textures mapping and blending is presented. In the light of Phong illumination model, an unit spherical surface under the same shading environment as the actual volume rendering is employed to emulate the real reflectional light of per-voxel, and a look-up table of voxels' reflectional lights indexed in their normal N is made, on which the illumination of per-voxel may be quickly ascertained. Volumetric Data window transform modulated by voxel's gradients is used to compute per-voxel opacitya. The data set composed of all voxels' illuminations (RGB) and opacitiesαis projected from object space into view space by textures mapping, and is blended from back to front along view direction into 2D image with 3D vision effect. Matrix transform of degree rotation of 3D object is used in observing in different viewing directions, and a fast equivalent method of shading correction about it is brought forward to improve its interaction speed in volume rendering process. The excellence of data processing software and texture mapping hardware of volume rendering is colligated in the algorithm. It is experimented by using 2D textures mapping and blending in general personal computers. High-quality images may be produced at nearly interactive speeds. The algorithm may be also applicable for volume rendering based on 3D texture mapping.