在建筑规划和历史遗迹重建等领域，需要在重建的场景中添加、删除虚拟物体。能否获得图像拍摄时刻的光照信息，是决定最终合成图像的照片级真实感程度的重要因素之一，本文对基于单幅建筑物图像的光源方向检测技术进行了研究。把户外的太阳光看作为平行光，在建筑物坐标系中其方向可以用方位角和仰角表示。利用图像中建筑物表面阳光强度值的变化来确定方位角。在此基础上，可以利用建筑物表面突出部分与其阴影之间的关系来确定仰角。这项技术可以应用于大多数建筑物的重建系统中。

When users want to plan the reconstructed virtual scenes, if we obtained the information of the lighting at the time when the images were taken, we can use the rendering technologies from computer graphics to obtain new synthesized photorealistic imageries. This paper presents techniques for recovering the tilt angle of solar illuminant from a single outdoor building image, which can be integrated to most current image-base architectural rebuilding systems. Solar illumination can be treated as parallel light. Its direction can be measured by tilt and slant angle in architectural coordinate system. To calculate the tilt angle, we utilize the changes of intensities from different wall surfaces. This idea comes from SFS (Shape from Shading) technique. On the basis of the calculated tilt angle, we can easily calculate the slant angle from images by using the bulges of the wall surface and their shadows.