X-RAY PHASE-CONTRAST TOMOGRAPHY APPLIED TO VIRTUAL UNFOLDING OF HERCULANEUM PAPYRI
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Stabile, Sara
Cipparrone, Gabriella
Cedola, Alessia
Bukreeva, Inna
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UNIVERSITA’ DELLA CALABRIA
Dipartimento di Fisica
Dottorato di Ricerca in
Scienze e Tecnologie Fisiche, Chimiche e dei Materiali in convenzione con il CNR
CICLO
XXXII; In 1750 a large villa on a hill overlooking Herculaneum and the Bay of Naples was discovered.
This villa probably once belonged to the wealthy Roman aristocrat Lucius Calpurnius Piso
Caesoninus, a well-known Roman politician, who was a patron of Epicurean philosophers.
The villa was lost from history in A.D. 79 in the catastrophic eruption of Mount Vesuvius
when it was buried by tons of thick volcanic mud which gradually hardened to a concrete-like
consistency.
During villa excavations, workers discovered many important works of art and an impressive
library of some 1800 papyri rolls - thus the name Villa of the Papyri. The library consists
of a remarkable collection of Epicurean philosophical texts written in Greek, and a lesser
number of Latin texts.
Due to the intense heat of the volcanic flow and the pressure exerted by the weight of mud,
lava, pumice, and rubble, these rolls are extremely fragile, lost more or less the original
cylindrical shape, and the individual sheets stuck together tenaciously.
Since their discovery, numerous efforts have been made to open the carbonized-Herculaneumpapyri
and read the priceless information contained in them employing several manual and
destructive techniques.
My Ph.D. research work concerns the study of Herculaneum papyri using a non-destructive
X-ray technique and a new set of numerical algorithms for ‘virtual-unrolling’.
In particular, I used X-ray-micro-computed tomography (μX-CT) and X-ray Phase Contrast
Tomography (XPCT) as powerful non-destructive testing techniques for the full-volume
inspection of the papyri, able to give morphological and physical information on the inner
structure of the investigated sample. I analyzed three Herculaneum papyri fragments:
PHerc.1103 and PHerc.1105 belonged to the scroll exterior part, scorza, and PHerc.110
belonged to a papyrus partially unrolled in 1867.
The main purpose of my research work was building a computational platform for the
virtual 3D investigation of the Herculaneum papyri fragments. Due to the poor conditions
of the fragments, virtual operations on the 3D tomographic images, such as segmentation
and flattening of the papyrus sheets, result complicated and require an approach developed
specifically for this particular task.
In this thesis, I describe in detail this computational platform, which is the composite result
of 3D data digitisation, segmentation, modelling, flattening and texture mapping of papyrus
sheets. Following 3D data digitisation, the segmentation step is presented, thanks to which I
can digitally identify the single papyrus sheet within the volume. After the sheet surface is
modeled using triangular meshing, preferred to other kinds of mesh because it simplifies the
math and allows for faster operations. Finally, I focus on the parameterization methods for
unfolding sheet with minimum distortion. Once the good parametrization method has been
identified, the next step is texturing, i.e., assignment of 3D color information to each point
on a 2D mesh. The resulting texture reveals the features of the flattened sheet.
Besides, investigations on different phase retrieval approaches have been performed.
I implemented and tested three of the widespread methods to find the best one. Another
challenging problem, due to the ring artifacts present in the reconstruction that disturbs the
image impression, was resolved through algorithms adapted to this particular case. The
artifacts removal process allowed the visualization of clean slices and helped to reveal traces
compatible with writing. It has so been demonstrated the benefit of applying the XPCT
technique to trace handwriting.
Some of the results of this research are reported in the following paper has been accepted
for publication: Stabile S., et al., Computational Platform for the virtual unfolding of
Herculaneum Papyri, Sci. Reports.Soggetto
Applied physics; X-ray imaging techniques; Apllied mathematics; Virtual unfolding
Relazione
FIS/07;