  Light interreflections occurring in a concave object generate a color
gradient which is characteristic of the object's spectral reflectance. In this
paper, we use this property in order to estimate the spectral reflectance of
matte, uniformly colored, V-shaped surfaces from a single RGB image taken under
directional lighting. First, simulations show that using one image of the
concave object is equivalent to, and can even outperform, the state of the art
approaches based on three images taken under three lightings with different
colors. Experiments on real images of folded papers were performed under
unmeasured direct sunlight. The results show that our interreflection-based
approach outperforms existing approaches even when the latter are improved by a
calibration step. The mathematical solution for the interreflection equation
and the effect of surface parameters on the performance of the method are also
discussed in this paper.
