Photomacrography and RTI
ICACH lab has been using experimental methods in order to trace deposits from plants on stone grinders used in
More specifically the techniques and the equipments employed are:
Reflectance Transformation Imaging (RTI)
Custom domical structure with 36 Halogen Emmiters(12v)
Canon Mark II 5D – Full sensor – 24 Megapixels
Canon EF 50mm f/1.4 USM Lens – fixed lens (distortion free)
TCL microcontroller for automatic acquisition of imagery
Photomacrography – Large Format Scanning
Sinar F monorail system
Better Light 4×5 Digital trilinear RGB scanning back
Super 6k-HS -108 MP
6000 x 8000 pixels – Native CCD resolution
137 MB max. file 24-bit RGB (274 MB in 48-bit RGB)
Cobalt #0 – Rodenstock Apo Macro Sinorar Lens – 120mm (equivalent 35mm)
1:1 reproduction ratio.
Reflectance Transformation Imaging (RTI) has been performed on three stones at various angles. RTI consists of 36 images taken from predetermined angles from a stationary camera in order to map luminance data on to surface. The rendered digital image can then be examined virtually by manipulating the light angle along the surface thus enhancing surface texture. This operation has been done in the visible spectrum.
A custom-build RTI dome that produces PTM files consists of a hemispherical domical device with a hole at the apex, and thirty-six halogen lights embedded at randomly fixed intervals around the dome and controlled by a by using a pre-scripted programmable microcontroller. The stone is placed at the base of the dome, while a camera is positioned looking downward focusing, through the hole at the top, on the aforementioned object. Thirty-six photographic images are sequentially taken, each with a single light shining on the artefact, thus creating thirty six images with different light angles. Then, the PTM algorithm synthesizes the data from these images to create a single high resolution image that can be examined on a PTM viewer with a “virtual torch”. The viewer allows the user to move the light angle intuitively in real time, so that the combination of light and shadow representing the relief features of the object’s surface can be freely altered. RTI also permits the enhancement of the subject’s surface shape, color and luminance attributes, which extracts detail out of the surface that cannot be otherwise derived.
Photomacrography or close-up photographic scanning or Large Format Scanning is done at approximately 5 to 15 cm distance lens to surface and by using the large format camera with a distortion free lens at 1:1 reproduction ratio. The dynamic range and the interplay of light and colors along the high fidelity morphological texture can be extracted and rendered in a single digital file that encapsulates a huge amount of chromaticity, texture and luminosity values.
This technique involves the photography of small objects or details of larger objects thus creating highly magnified images of the fibers, particles or microstructures that make up an object. Photomacrography can be elaborated for a wide range of materials and sizes.
The LF system at The Cyprus Institute is appropriately customized to meet the challenges of archaeological material from Cyprus and the region.
Photomacrography and RTI by ICACH is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.