Received October 20, 1997; revised manuscript received August 10, 1998; accepted August 11, 1998 We introduce a new process of shape estimation through the matching of photometric-stereo images, which are monocular images obtained under different illuminations. If the illumination directions are not far apart, and if the imaged surface is smooth, so that a linear approximation to the reflectance map is applicable, the disparities produced by the matching process can be related to the depth function of the imaged surface through a differential equation whose approximate solution is easily found. We thus obtain a closed-form expression for surface depth, depending only on the coefficients of the linear-reflectance-map function. If those coefficients are not available, a simple iterative scheme still allows the recovery of depth, up to an overall scale factor. # 1998 Optical Society of America [S0740-3232(98)01211-3] OCIS codes: 150.0150, 150.4620, 330.1400.
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