Photometric stereo for outdoor webcams

Abstract

We present a photometric stereo technique that operates on time-lapse sequences captured by static outdoor webcams over the course of several months. Outdoor webcams produce a large set of uncontrolled images subject to varying lighting and weather conditions. We first automatically select a suitable subset of the captured frames for further processing, reducing the dataset size by several orders of magnitude. A camera calibration step is applied to recover the camera response function, the absolute camera orientation, and to compute the light directions for each image. Finally, we describe a new photometric stereo technique for non-Lambertian scenes and unknown light source intensities to recover normal maps and spatially varying materials of the scene

One-day outdoor photometric stereo via skylight estimation

“…Ackermann et al [3] and Abrams et al [1] use time-lapse sequences captured by static outdoor webcams. Since both approaches model the illumination as a distant point light (the sun) with a constant ambient light, they require many months of images to avoid coplanar light directions in photometric stereo.…”

“…It is a huge optimization using 500 images of careful selection. Ackermann et al [3] present a process of image filtering and selection to find 50 proper images from 20k candidate images.…”

Photometric Stereo in the Wild

“…There are a few methods, such as the ones described in [20,21,1,27], that study PS for outdoor scenes. While these approaches address some specific problems, we propose a simple and general technique to allow data acquisition in an uncontrolled environment.…”

Photometric Ambient Occlusion

“…Some notable examples include recovering surface normals using photometric stereo [6,25,2], recovering diffuse reflectance and illumination as intrinsic images [27,15], and computing low-dimensional models of appearance of objects and scenes [26,9]. However, these methods typically disregard the effect of the local visibility of illumination in determining shading.…”