Tuesday, January 01, 2013

Heliometric Stereo: Shape from Sun Position - implementation -

Let's start the year by finding where the sun is and an impementation on how to do that automatically with uncalibrated images. 

Heliometric Stereo: Shape from Sun Position by Austin Abrams, Christopher Hawley, and Robert Pless. The abstract reads:
In this work, we present a method to uncover shape from webcams "in the wild." We present a variant of photometric stereo which uses the sun as a distant light source, so that lighting direction can be computed from known GPS and timestamps. We propose an iterative, non-linear optimization process that optimizes the error in reproducing all images from an extended time-lapse with an image formation model that accounts for ambient lighting, shadows, changing light color, dense surface normal maps, radiometric calibration, and exposure. Unlike many approaches to uncalibrated outdoor image analysis, this procedure is automatic, and we report quantitative results by comparing extracted surface normals to Google Earth 3D models. We evaluate this procedure on data from a varied set of scenes and emphasize the advantages of including imagery from many months.
The project page and attendant code is here.

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