Ellipsometry techniques allow to measure polarization information of materials, requiring precise rotations of optical components with different configurations of lights and sensors. This results in cumbersome capture devices, carefully calibrated in lab conditions, and in very long acquisition times, usually in the order of a few days per object. Recent techniques allow to capture polarimetric spatially-varying reflectance information, but limited to a single view, or to cover all view directions, but limited to spherical objects made of a single homogeneous material. We present sparse ellipsometry, a portable polarimetric acquisition method that captures both polarimetric SVBRDF and 3D shape simultaneously. Our handheld device consists of off-the-shelf, fixed optical components. Instead of days, the total acquisition time varies between twenty and thirty minutes per object. We develop a complete polarimetric SVBRDF model that includes diffuse and specular components, as well as single scattering, and devise a novel polarimetric inverse rendering algorithm with data augmentation of specular reflection samples via generative modeling. Our results show a strong agreement with a recent ground-truth dataset of captured polarimetric BRDFs of real-world objects.

翻译：椭偏技术能够测量材料的偏振信息，但需要精确旋转不同光路与传感器配置下的光学元件。这导致采集设备笨重，需在实验室条件下精细标定，且单次物体采集时间通常长达数天。现有技术虽可获取偏振空间变化反射信息，但仅限于单一视角；或能覆盖全视角方向，却仅适用于单一均匀材料的球体物体。我们提出稀疏椭偏法——一种便携式偏振采集方法，可同步捕获偏振SVBRDF与三维形状。手持设备由现成固定光学组件构成，单物体采集总时长从数天缩短至二十分钟至三十分钟。我们建立了包含漫反射、镜面反射及单次散射分量的完整偏振SVBRDF模型，并设计了新型偏振逆渲染算法，通过生成式建模对镜面反射样本进行数据增强。实验结果表明，该方法与近期采集的真实物体偏振BRDF基准数据集高度吻合。