This paper presents a photometric stereo method that works with unknown natural illumination without any calibration objects or initial guess of the target shape. To solve this challenging problem, we propose the use of an equivalent directional lighting model for small surface patches consisting of slowly varying normals, and solve each patch up to an arbitrary orthogonal ambiguity. We further build the patch connections by extracting consistent surface normal pairs via spatial overlaps among patches and intensity profiles. Guided by these connections, the local ambiguities are unified to a global orthogonal one through Markov Random Field optimization and rotation averaging. After applying the integrability constraint, our solution contains only a binary ambiguity, which could be easily removed. Experiments using both synthetic and real-world datasets show our method provides even comparable results to calibrated methods.

中文翻译：

---

自然照明下基于补丁的未校准光度立体。

本文提出了一种光度立体方法，该方法适用于未知的自然光照，无需任何校准对象或目标形状的初始猜测。为了解决这个具有挑战性的问题，我们建议对由缓慢变化的法线组成的小表面块使用等效定向照明模型，并将每个块解决到任意正交模糊度。我们通过补丁和强度分布之间的空间重叠提取一致的表面法线对，进一步构建补丁连接。在这些连接的指导下，通过马尔可夫随机场优化和旋转平均，将局部模糊度统一为全局正交模糊度。应用可积性约束后，我们的解决方案只包含一个二元歧义，可以很容易地删除它。