Photometric Stereo
Encyclopedia
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. 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.
, known point-like distant light sources, and uniform albedo
— the problem can be solved by inverting the linear equation
, where 
is a (known) vector of 
observed intensities, 
is the (unknown) surface normal, and 
is a (known) 
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. Current research aims to make the method work in the presence of projected shadows, highlights, and non-uniform lighting.
Computer vision
Computer vision is a field that includes methods for acquiring, processing, analysing, and understanding images and, in general, high-dimensional data from the real world in order to produce numerical or symbolic information, e.g., in the forms of decisions...
for estimating the surface normals of objects by observing that object under different lighting conditions.
The technique was originally introduced by Woodham in 1980. 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.
Methods
Under Woodham's original assumptions — Lambertian reflectanceLambertian reflectance
If a surface exhibits Lambertian reflectance, light falling on it is scattered such that the apparent brightness of the surface to an observer is the same regardless of the observer's angle of view. More technically, the surface luminance is isotropic...
, known point-like distant light sources, and uniform albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
— the problem can be solved by inverting the linear equation
, where is a (known) vector of observed intensities, is the (unknown) surface normal, and is a (known) 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. Current research aims to make the method work in the presence of projected shadows, highlights, and non-uniform lighting.