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Title
New perspectives to save cultural heritage
Author
Altan, M. Orhan

55
med media:
99. pp. 17-
ie National
a profound
Information
mal Library
I discussion
RE-SEQUENCING A HISTORICAL PALM LEAF MANUSCRIPT WITH
BOUNDARY-BASED SHAPE DESCRIPTORS
D. Akca , A. Gruen
Institute of Geodesy and Photogrammetry, Swiss Federal Institute of Technology (ETH) Zuerich
ETH Hoenggerberg, CH-8093 Zuerich, Switzerland. E-mail: (akca, agruen)@geod.baug.ethz.ch
KEY WORDS: Cultural Heritage, Image Analysis, Boundary-tracing, Fourier descriptors, shape similarity measures, Tree-Search,
Visualization
ABSTRACT:
A stack of 66 historical Indian palm leaves, which were produced in the 8 th Century AD, is kept in the Museum Rietberg, Zuerich.
On the leaves, there are figures and a long poem, inscribed in ancient Sanskrit language and narrating a love story. The original
sequence of the leaves was lost long time ago. At one point in history, the stack of the leaves was damaged by a mouse biting pieces
off. Only the first 18 leaves have their pages numbered in Sanskrit language, but the rest of them got out of order. If it is assumed
that the mouse chewed at the leaves in a regular manner, the geometry of the leaf perimeter, as left over after eating, should bear
useful information to find the original sequence. After acquiring digital images of the leaves and a pre-processing phase, an inner
boundary-tracing algorithm was applied to all leaves in order to segment them. The fundamental data used in this work are boundary
coordinates of the leaves. In order to obtain quantitative shape similarity measures, two different Boundary Based Shape Descriptor
algorithms were applied to the boundary data: Fourier descriptors and a rotation-translation invariant boundary intersection-based
shape descriptor. Shape descriptors indicate the similarity of different leaves. These similarity measures among all of the leaf pairs
were arranged in form of a symmetric square matrix. With this matrix and a threshold similarity value one can determine the most
probable ancestor and successor leaves for a pointed leaf. In the final step, a Tree Search scheme that starts from the 18 th (fixed) leaf
and ends at the 66 th (relaxed) leaf was established to generate the most probable sequence. Every node in the tree was defined as a
leaf and branched to the most probable neighbor leaves. The similarity measures were expressed as costs of the arcs, which connect
two nodes in the tree. The sequence which has minimum total path cost was proposed as the most probable original sequence.
1. INTRODUCTION
In the collection of Museum Rietberg Zuerich is an old palm
leave manuscript from India, consisting of 66 folios, inscribed
on both sides. Originally, they had all the same dimensions and
were once tightly bundled. On them are 100 erotic poems by a
8 th century AD Sanskrit poet (by the name of Amaru) inscribed,
many of which are illustrated with one or more pictures. The
manuscript was prepared about 200 years ago to be kept as a
bundle. All folios have a hole in the center through which a
string was drawn to tie all leaves tightly between two wooden
boards (Figure 1). However, the sequence of these poems is
unknown (Fischer, 2002). The manuscript was kept for two
centuries in an Indian library. Some time ago, a mouse did start
to eat part of these folios. It is likely that at that time, the right
sequence was still established, which was later lost, except at
the beginning: Folios 1-18 are paginated and therefore their
sequence is known. The mouse did not destroy the entire
manuscript. She nibbled only about 5-10 % away from each
leaf, mostly at the left side (Figure 2). If it is assumed that the
mouse ate the leaves in a regular manner, the geometry of the
leaf perimeter, as left over after eating, should bear useful
information to find the original sequence.
Since the rest of the leaves does not give any information about
the sequence, we must focus only the geometry of the harmed
part in order to avoid irrelevant data. The holes in the center of
the leaves constitute a base point that is approximately at the
same position on the all leaves. After the pre-processing phase
i.e. rectification, the harmed left parts were cropped from the
full images, and saved as different image files. All processes
were performed based on these cropped images.
After acquiring digital images of the leaves and a pre
processing phase, an inner boundary-tracing algorithm was
applied to all leaves in order to segment them. The fundamental
data used in this work are boundary coordinates of the leaves.
In order to obtain quantitative shape similarity measures, two
different Boundary Based Shape Descriptor algorithms were
applied to the boundary data: Fourier descriptors and a
rotation-translation invariant boundary intersection-based
shape descriptor. Shape descriptors indicate the similarity of
different leaves. These similarity measures among all of the leaf
pairs were arranged in form of a symmetric square matrix. With
this matrix and a threshold similarity value one can determine
the most probable ancestor and successor leaves for a pointed
leaf.
Figure 1: Front face of a leaf with hole for bundling up. Left perimeter side is damaged by the mouse.