Pentland (1987) proposed an algorithm for sensing scene depth by measuring the amount of defocus of an image. The algorithm is interesting in the sense that no correspondence problems are involved. The authors discuss the difference between shape from defocus and shape from focus and then present a two-phase algorithm where the defocus process is modeled as a two-dimensional Gaussian point-spread function. During the first phase (calibration phase), a camera system parameter is determined off-line. In the next phase (depth-recovery phase), this parameter is used to recover on-line the scene depth by taking two images of the same scene, but with a different amount of defocus. Some implementation issues are addressed, and test results on real images are provided.
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