摘要
目的基于双向反射分布函数的重要性采样方法在渲染物体材质表面时有极佳的拟真度,但采样方式存在复杂和高硬件存储开销的问题。针对上述问题,提出了一种基于权重生成和向量线性插值的采样方法用于解决该问题。方法在对出射光线方向进行计算时,通过给定的入射光方向、法线方向与物体表面材质光滑度参数,首先计算镜面反射光线方向,再结合余弦与指数函数二者的函数特性生成具有一定分布特征的权重值,并将镜面反射方向与随机生成的漫反射方向进行线性插值,其插值权重即为上述生成的权重值,最后规范化得到具有一定分布特征的新的出射方向。结果本文基于该快速采样方法,给出了路径追踪渲染算法的一套完整实现,并利用本文算法,从常见各类物体表面中抽取9种进行渲染,将所得实验结果与通过原始双向反射分布函数采样算法所渲染得到的实际结果进行比较,发现利用快速采样算法后渲染速度可提升1. 52 1. 99倍,且由于近似所造成的相对误差可控制在8%以内,并将原本用于描述物体表面的34 MB数据量降为仅几个浮点数的数据量,可知上述采样方法既具有极低硬件存储开销的特点,其渲染的图片又能保有较高的拟真度。随着光滑度参数的连续变化,可使得被渲染的物体表面由理想漫反射到理想镜面反射之间均匀过渡,从而统一了漫反射、高光反射与镜面反射三者的采样形式。结论本文使用简化的出射光方向采样算法替代传统BRDF重要性采样算法,并配套给出基于新采样算法实现的一套完整的路径追踪渲染方法,使得在不失真实度的情况下使得计算机在模拟漫反射、高光反射与镜面反射的形式得以简化与统一。本文方法亦可作为现有诸多采样方法的替代方案,其极低的存储开销优势可用于渲染含有大量不同材质的复杂场景;在渲染一般的粗糙�
Objective An importance sampling method based on bidirectional reflectance distribution function （BRDF） has excellent fidelity when rendering the surface of an object. However, this sampling method has a complicated form and can lead to heavy hardware storage cost, which can cause many problems when applied to practical use. These problems include high implementation complexity, low execution efficiency, and high debugging difficulty. Owing to these problems, this study provides a new method for computing the reflection direction of a light path. The new method uses weight generation technique and vector linear interpolation. This method not only reduces the complexity of the algorithm but also reduces the computational complexity of many previous sampling algorithms. The new method is also easy to implement. Method Thealgorithm initially calculates the direction of reflected light and subsequently combines the features of cosine and exponential functions given the direction of incident light and surface normal. This algorithm generates a weight value that has a certain distribution characteristic. The algorithm defines a parameter called ~ to enable the distribution characteristic to be control- lable. The surface tends to exhibit a diffuse reflection for each incoming light ray when s is relatively small. Otherwise, the surface tends to exhibit an ideal mirror reflection. The new algorithm performs a linear interpolation between a mirror and diffuse reflection directions to obtain a new vector after the weight generation process, and the weight that was generated previously was used in this process. Finally, the algorithm obtains the desired reflection direction of a light ray by normali- zing the new vector. This method efficiently simulates glossy surfaces, which exist vastly in real life. Result This study conducts a full implementation of the path tracing algorithm. The new algorithm is based on the new sampling method de- scribed previously. Nine kinds of common surface materials are selected for the r
作者
刘成浩
Liu Chenghao(Beijing Institute of Technology-School of Information and Electronics,Beijing 100081,China)
出处
《中国图象图形学报》
CSCD
北大核心
2018年第11期1707-1719,共13页
Journal of Image and Graphics
