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Image-based relighting methods require multiple images of a static object under varying, known lighting directions. A simple way of collecting these images and light directions is to place a shiny black or red sphere in the scene before capturing a number of images illuminated by an external light source (such as photographic flash) from various directions. A simple approach is to set a digital camera on a tripod and set a handheld flash to trigger the camera. Move the handheld flash to various positions, keeping it a fixed distance to the object being photographed. If these images are placed in a directory, and that directory specified in the PTMbuilder application, highlights appearing in the ball will be automatically found for each image. The software will then compute light directions from these highlights and construct a PTM from the images automatically.  

This PTMbuilder software can be freely downloaded (URL for PTM Builder Software License) and was jointly developed by teams at HP Labs and at University of Minho, Portugal (Joao Barbosa, Joao Sobral and Alberto Proenca). At present, the software runs on Windows or Linux, but Apple systems are currently not supported. Once downloaded and unzipped, the process is started by double-clicking on the LPtracker.jar file. The program starts by prompting you to specify a directory containing images with varying lighting directions, each containing a shiny red or black ball.  

Suitable reflective spheres are available from various suppliers, two sources are here and here. An example of highlight based captured is discussed in the VAST 2006 paper available from  Tom Malzbender’s home page.

 *image credit: Cultural Heritage Imaging, 2007.

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