增强现实系统中，解决虚拟物体表面光照情况与真实环境匹配问题关键的一步是进行光源追踪。基于标志点注册及具有漫反射特性的探测球提出一种光源追踪算法〖JP3〗。该算法仅对一幅被单一光源照射的标志立方体和探测球图像进行分析，利用图中标志点确定探测球相对照相机的位置、姿态关系，利用探测球表面的亮度信息推算光源向量。该探测球图像要进行一系列图像处理程序，其中等亮度线的提取及拟合是关键步骤。实验结果表明，本文算法能够达到预期效果，较好地实现了光源追踪，适用于各种位置的单一光源照射情况及基于标志点注册的增强现实系统。

In order to integrate a virtual object in a real scene seamlessly in augmented reality(AR）system,we need to simulate the interactions of the virtual object with the illumination of the scene.Acquiring the knowledge of illuminant direction is crucial in this work.We present a novel approach for estimating the direction from a single image of a scene that is illuminated by a light source regardless it is point light source or directional one.We propose to employ a maker cube,which is used to register to determine the rigid transformation relating 2D images to known 3D geometry,and a lambertian probe sphere,which is used to estimate the light source direction by image processing.The key process is to find and extract the intensity occluding curve on the sphere.Experimental results show that our approach is computationally efficient and the light source direction can be accurately obtained by it.