PTM Dome Construction

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PTM Dome Construction
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Minimum Requirements

• Repeatable Lighting locations
• Recommend at least 50 positions
• Light position file
• Computer and PTM software
• Digital camera

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Lighting Locations

• Positions should be evenly distributed around
  hemisphere
• 50 positions will evenly cover hemisphere
• Additional positions give smoother transitions
• Lighting sequence must be consistent

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Creating a Light Position File

• Lighting positions measured in X, Y, Z coordinate
  system
• Measurements converted to normalized vector values

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Conversion to Vector Value

• Square root X2Y2Z2
• Divide X, Y, Z coordinates by this value to
  normalize
• Calculate for each light position

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Light Position File

• .txt file in column format
• Image number and then normalized vector values
• Image number must correspond the light position
  used to capture the image

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Computer

• Modern computers are adequate
• Recommend a minimum of 1GB RAM and 60GB storage
  space
• Increased memory and graphics processing improves
  performance
• Large image files require additional computing
  power and storage

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Software

• PTM software runs through DOS
• Two separate components to software
• PTM Fitter
• Fitter program is run separately after image
  capture
• Creates .ptm file from images and LP file
• Recognizes .jpg image format
• PTM Viewer
• Opens .ptm files for viewing

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Digital Camera

• Position and settings must not be altered during
  image capture
• SLR Style Camera
• Sufficient resolution for application
• Software development kit (SDK)
• USB or IEEE connection if automating

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Automation

• Camera shutter must be synchronized with lights.
• Controller box built to fire and sequence
  flashes.
• Modified camera SDK controls timing of lights and
  camera shutter
• Images downloaded to designated folder

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Automation (cont.)

• Simple .bat files created to number LP file and
  run PTM fitter program.
• Image files could also be renamed to use with a
  static LP file.
• Adobe Photoshop program allows batch processing
  of captured images.
• Rename, Change file format, Crop, Resize, etc.

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Design Considerations

• Light output determines radius of hemisphere
• Brighter flashes need more distance (radius) from
  object
• Radius of hemisphere determines overall size
• Camera positioning
• Distance/focal length combination

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Design Considerations (cont.)

• Crime Scene use
• Mobility
• Contact area
• Weather
• Power
• Clean up

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Additional Information

• http//www.hpl.hp.com/research/ptm/ri.html
• Reflectance Imaging
• http//www.hpl.hp.com/research/ptm/se.html
• Reflectance Transformation
• http//palaeo-electronica.org/2002_1/fossils/issue
  1_02.htm
• Paper on Fossil imaging using PTM technique
• http//www.hpl.hp.com/personal/Tom_Malzbender/pape
  rs/egrw2006.pdf
• Paper on surface enhancement with PTM technique.