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PTM Dome Construction

PTM Dome Construction. Minimum Requirements. Repeatable Lighting locations Recommend at least 50 positions Light position file Computer and PTM software Digital camera. Lighting Locations. Positions should be evenly distributed around hemisphere 50 positions will evenly cover hemisphere

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PTM Dome Construction

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  1. PTM Dome Construction

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

  3. 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

  4. Creating a Light Position File • Lighting positions measured in X, Y, Z coordinate system • Measurements converted to normalized vector values

  5. Conversion to Vector Value • Square root X2+Y2+Z2 • Divide X, Y, Z coordinates by this value to normalize • Calculate for each light position

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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

  13. Design Considerations (cont.) • Crime Scene use • Mobility • Contact area • Weather • Power • Clean up

  14. 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/issue1_02.htm • Paper on Fossil imaging using PTM technique • http://www.hpl.hp.com/personal/Tom_Malzbender/papers/egrw2006.pdf • Paper on surface enhancement with PTM technique.

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