SHAPE FROM SHADING USING WAVELET TRANSFORM
利用小波变换由明暗度恢复表面形状

In shape from shading, iterative algorithms are often used to compute the surface derivatives. These algoritghms are, however, very time-consuming when the iterations are performed on the original image. In this paper the authors propose a multiresolution method which makes use of the orthonormal wavelet transform to construct a multiresolution pyramid and let most iterations be performed on the low resolution images to give good predictions of the initial values of the surface derivatives of higher resolution images and thus save many computations. On the other hand, the nonlinearity of imaging makes the direct reduction of the image resolution not an optimal way of utilizing the multiresolution method. Instead, they construct the pyramid of the norm of the surface direction. They prove that this strategy gives out excellent results when the surface is smooth and the support length of the wavelet is small. Factors that may affect the selection of the wavelet in the multiresolution shape form shading are also studied. Experiments show the superiority of this strategy to other methods.