Abstract

Many previous works on photometric stereo have shown how to recover the shape and reflectance properties of an ob ject using multi- ple images taken under a fixed viewpoint and variable lighting conditions. However, most of them only dealt with a single point light source in each image. In this paper, we show how to perform photometric stereo with four images which are taken under distant but general lighting condi- tions. Our method is based on the representation that uses low-order spherical harmonics for Lambertian ob jects. Attached shadows are con- sidered in this representation. We show that the lighting conditions can be estimated regardless of ob ject shape and reflectance properties. The estimated illumination conditions can then help to recover the shape and reflectance properties.