CC BY
9The 30th International Conference on Advanced Laser Technologies
N-I-7
ALT'23
Terahertz imaging and spectroscopy for heritage science
Olga A. Smolyanskaya
Heritage Science lab, ITMO University, Saint-Petersburg, 197101 Russia
Heritage science is a field of complex research, located at the junction of the humanities and the fine sciences: history, art history, archeology, sociology and urban studies, and at the same time - chemistry, physics and biology. In our country, a unique school of art history and restoration has been formed, combining the accuracy of the humanistic approach with the careful methods of preserving cultural heritage monuments. This was largely due to the emergence of technical and technological research laboratories at museums and restoration centers.
One of the most difficult problems for museum restorers and technologists is non-destructive studies of multilayer coatings. Traditional museum methods, such as x-ray radiography, infrared reflectography, give an integrated picture of all layers and it is almost impossible to determine the sequence of layers and highlight the layer of interest. For this purpose, the terahertz time-domain spectroscopy (THz-TDS-based) object visualization system can be useful. Due to non-invasive properties of THz radiation, such a system allows to be applied for investigation of an object of art.
The main goal of this study was to test the detecting capacity of such a system to identify layers of paint below the surface. We have used a unique test-object, mimicking the most common tasks for painting investigation. The image of paints on canvas was recorded using the TeraPulse LX (TeraView, UK) system with a spectral range 0.06 THz - 6.00 THz. Due to the high sensitivity of THz radiation to the distinction between the optical properties of painting materials, this experiment allowed us to obtain detailed information about the structure and spectroscopic data of layers of objects and pigments, and determine the shape of invisible elements without damaging the canvas. Thus, the THz imaging method can be very useful in restoration work designing, determining defects in the structure of paintings materials, as well as when searching for hidden objects under layers of paint.
Our research is dedicated as well to the investigation of image processing methods applied to THz images of painting. To our best knowledge, there is no comprehensive research on enhancement of THz images of art objects. Previous research in THz imaging concerned different image processing methods but were not applied to the objects of art. However, artworks appeared to be more complicated to reconstruct and process by means of THz imaging, which might be related to the specific structural data, unique for every object. Algorithms of enhancement were created and applied to the images of painting's inner layer. The details on these images became sharper and more distinguishable. The results were quantified by PSNR value, which increased in every case. The intensity histograms and the intensity spectra before and after processing were compared. The obtained results can be regarded as positive and, therefore, these image processing methods can be interesting for the purposes of artworks investigation before restoration.
