Surface Topography of Cuneiform Tablets

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Surface Topography of Cuneiform Tablets

• Monica Barbu and Robert H. Johnston, and
  Jonathan S. Arney
• Chester F. Carlson Center for Imaging Science
• Rochester Institute of Technology

2
Overview

• Background
• Theory
• Accomplishments
• Summary

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Cuneiform Tablet

• First form of writing.
• 5cm.length 4cm.wide 1cm.high.
• Evolved from pictographs.
• Used as documents about property, inventory and
  taxes.
• Consist of wedge marks and cylinder seal
  impressions.

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The Challenges of Photographing Cuneiform Tablets

• Transfer 3-dimensional characteristics to a
  2-dimensional plane.
• In the past
• Artists hired to draw the features - time
  consuming and subjective.
• Nearfield microscopy - expensive.
• Proposed technique
• Surface Topography - simple equipment and
  inexpensive.

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Surface Topography
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Surface Topography

• Calculating the topography of an object from
  digital images is a distinct way of extracting
  contour measurements.
• Described as variation in height across a
  horizontal dimension.
• Results in the quantitative relationship between
  surface angle and the observed irradiance in the
  camera.

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Surface Topography

• Provides relationship between topography and
  irradiance.
• The surface of the object is a Lambertian
  reflector.

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Schematic representation between topographic
height, h and the surface angle, ?
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Surface Topography
Characteristics of the two images in one
dimension is
I1(x) IoR sin ?01 ?(x)
I2(x) IoR sin ?02 ?(x)
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Capturing images with novel device

• One light source attached to a graded arc.
• The arc has the ability to be positioned at any
  degree from the base.
• The arc is attached to a ring which is free to
  move 360º around the object.
• The object is stable in the center of this ring.

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Capturing the Images
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Flat Fielding

• Calibrate the camera, in order to use the digital
  camera as a primary instrument for measuring
  light.
• Flat fielding the images.
• Removes the side to side variation in brightness
  which is caused by non-uniform illumination.
• The result consists only the random variations
  caused by the surface of the object.

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Surface Topography of the Sphere
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Results

• Matrix of alpha values
• Scaled to 256 gray levels.
• 1-dimensional array across the center of the
  sphere extracted for analysis.

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Trace of Tan(alpha) Values Calculated Across the
Row of Pixel Values in the Scan Line
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Topographic Height Across the Scan Line
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Surface Topography of Cuneiform Tablet
Before
After
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Topographic Height Across the Scan Line from
the Cylinder Seal Impression
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Unfolded Tablet
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Conclusion

• Cuneiform Tablets are remains of historic
  cultural values.
• Surface topography would be beneficial in
  characterizing the evolution of these artifacts.
• Make these documents more accessible.
• Offer a clue to the specific tools used to make
  the impressions.