Photometric stereo 3D visualizations of rock-art panels, bas-reliefs, and graffiti

For small-scale cultural subjects, such as rock engravings, graffiti and bas-reliefs, 3D rendering may be realized by applying the photometric stereo consolidate method, instead of complex and expensive laser-scanning equipments. It is a cheap, portable, and easily implementable technique generally used in quality controls within manufacturing industrial environments or in robotic vision. Its main advantage is the use of common digital photography with portable flash lighting and dedicated software for data elaboration. Furthermore, it provides as output data, in addition to the morphological information of the objects, the map of brightness and surface colours (albedo), which allows the user correctly to identify the frescoes and paintings without distortions caused by shadows or other morphological detail. This paper deals with the theoretical fundamentals of the photometric stereo method for 3D rendering of surfaces, its practical implementation, and the mathematical strategies to obtain both the morphological data and the albedo functions. Some examples of applications on rock-art and other artefacts are presented and discussed.