12 February 2008 Deep shadows in a shallow box
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Abstract
We present a fast, low-cost technique to gather high-contrast 'relightable' photographs of desktop-sized objects. Instead of an elaborate light stage, we follow Mohan et al.; we place the object and a digitally steered spotlight inside a white cardboard box, aim the spotlight at the box interior, and move the spot to light the object from N repeatable lighting directions. However, strong ambient lighting from box interreflections causes 'shallow' shadows and reduces contrasts in all basis images. We show how to remove this ambient lighting computationally from the N images, by measuring an N ×N matrix of coupling factors between lighting directions using a mirrorsphere light probe. This linear method, suitable for any light stage, creates physically accurate 'deep shadow' basis images, yet imposes only a modest noise penalty, and does not require external light metering or illumination angle measurements. Results from our demonstration system support these claims.
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Xiang Huang, Xiang Huang, Ankit Mohan, Ankit Mohan, Jack Tumblin, Jack Tumblin, } "Deep shadows in a shallow box", Proc. SPIE 6810, Computer Image Analysis in the Study of Art, 681003 (12 February 2008); doi: 10.1117/12.766949; https://doi.org/10.1117/12.766949
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