A divide-and-conquer strategy in shape from shading problem

A divide-and-conquer strategy in shape from shading problem under fully perspective conditions is proposed for the information recovery of book surfaces. The whole recovery process is composed of three sequential steps: preprocessing, apparent shape recovery, and ortho-image generation. Pure shade images are extracted in the preprocessing step by introducing a phenomenological model of interreflection and by removing pigment parts from observed images. A recurrence relation is derived from the definition of mean slope in the discrete image. Theoretically, it becomes possible to recover unique shape without iteration using the derived equations in the case of a Lambertian cylinder. However, a feedback shape recovery process is implemented as a practical algorithm in order to overcome self-shadows. Results of simulations and real experiments show the properness and acceptability of the proposed strategy and implemented algorithms.