Polynomial Texture Mapping

[View interactive examples]

Polynomial Texture Mapping was invented by Tom Malzbender and colleagues at Hewlett Packard Labs. A Polynomial Texture Map (PTM) is like a photograph where the subject's lighting can be changed by the viewer.

Other non-naturalistic visualisation techniques can also be used, such as viewing just the specular highlights (which makes the object 'shiny') or surface normals (false colour, based on angles/direction of surface features). Light is extemely important in showing the detail of an object, and PTM can help to enhance those details to help us better understand and interpret an artefact.

This technology presents many important possibilities to archaeologists and museums. PTM allows us to study the surfaces of objects more closely, and share more detailed information about an object than has previously been possible at an affordable level.

PTM at Wessex Archaeology

After being introduced to the technology, a team at Wessex Archaeology began to experiment with Polynomial Texture Mapping. A PTM is made from many photos (48+, ideally), each lit from a different direction forming a 'dome' of lighting positions.

After testing manual processes, we decided to build a prototype system which would automate the capture process.

Illumination dome for the capture of Polynomial Texture MapsIllumination dome for the capture of Polynomial Texture Maps

An Arduino microcontroller is connected to 48 ultra bright LEDs in a 600mm acrylic dome, and a camera remote. Many hours were spent glueing, cutting wires, and soldering the LEDs into the circuit.

At the press of a button the capture sequence begins, and the lights turn on and off in sequence, synchronised with the camera shutter. The object inside the dome is in a controlled lighting environment, shielded from ambient light. The inside of the dome is matt black to minimise reflections. This allows us to capture high quality photographs to process into a Polynomial Texture Map.

Photographs are then processed into a PTM using software from HP Labs.