# Photometric stereo

(Redirected from Photometric Stereo)

Photometric stereo is a technique in computer vision for estimating the surface normals of objects by observing that object under different lighting conditions.

The technique was originally introduced by Woodham in 1980.[1] The special case where the data is a single image is known as shape from shading, and was analyzed by B. K. P. Horn in 1989.[2]

## Methods

Under Woodham's original assumptions — Lambertian reflectance, known point-like distant light sources, and uniform albedo — the problem can be solved by inverting the linear equation $I = n \cdot L$, where $I$ is a (known) vector of $m$ observed intensities, $n$ is the (unknown) surface normal, and $L$ is a (known) $3 \times m$ matrix of normalized light directions.

Photometric stereo has since been generalized to many other situations, including non-uniform albedo, extended light sources, and non-Lambertian surface finishes.[3] Current research aims to make the method work in the presence of projected shadows, highlights, and non-uniform lighting.