Abstract

Recovery of the shape of objects from their image shading has been addressed extensively for land environments. However, these techniques cannot be applied directly when the attenuation of light is significant and artificial lighting is the sole source of illumination, as in deep-ocean environments. To do this, we must take into account effects due to lighting and attenuation in addition to other factors corresponding to surface shape and reflectance properties. We present simplified equations for scene radiance and image irradiance that incorporate the effects of attenuation in the medium. Based on these, we derive the reflectance map for a Lambertian surface illuminated by a point source. We then show how the orientation of a Lambertian planar patch can be recovered from its image shading in closed form. More robust solutions are obtained when the distance to the surface is known. Some simplifications arise in the cases of illumination from a collimated light source and point-source illumination in a nonattenuating medium. Computer simulations and results of experiments with real images are presented to show the accuracy of these solutions.

© 1991 Optical Society of America

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