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Images and Artefacts of the Ancient World$
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Alan K. Bowman and Michael Brady

Print publication date: 2005

Print ISBN-13: 9780197262962

Published to British Academy Scholarship Online: January 2012

DOI: 10.5871/bacad/9780197262962.001.0001

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Shadow Stereo, Image Filtering, and Constraint Propagation

Shadow Stereo, Image Filtering, and Constraint Propagation

(p.15) Chapter 2 Shadow Stereo, Image Filtering, and Constraint Propagation
Images and Artefacts of the Ancient World

Michael Brady

Xiao-Bo Pan

Veit Schenk

Melissa Terras

Paul Robertson

Nicholas Molton

British Academy

It is agreed that stilus tablets are very important documentary sources, however they are the most difficult to decipher. The difficulties in deciphering them is due to the rough surface of the tablets, the low brightness contrast of the incisions, the dense wood-grain lines, and the badly stained and pitted nature of the tablets. All of these posit a challenge for conventional two-dimensional (2D) image analysis. This chapter aims to provide a system that would aid the historian in interpreting stilus tablets by improving the legibility of the tablets. It provides novel ways of determining the texts incised on the tablets. One of these is the use of three-dimensional (3D) image analysis techniques. Such a technique is capable of detecting incisions, compared to the 2D image analysis, and is portable and inexpensive. Another method that can be used is the use of shadow stereo. This method employs low raking angle light close to the plane of the tablet at different elevations. The chapter also discusses the image formation process and the process of choosing elevations for each azimuth direction. The chapter also includes a discussion on realizing the shadow stereo algorithm.

Keywords:   stilus tablets, 2D image analysis, 3D image analysis, incisions, shadow stereo, low raking angle light, elevations, image formation process, azimuth direction, shadow stereo algorithm

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