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Focus measure operator using 3D gradient

The shape from focus (SFF) is used to reconstruct a three-dimensional (3D) structure of objects from a sequence of two-dimensional (2D) images. The basic idea of image focus is that objects at different distances from a lens are focused at different distances. In SFF, focus measure operator is applied on the sequence of images. From the analysis of defocused image, it is observed that the focus measure operator should respond to high frequency variations of image intensity and produce maximum values when the image is perfectly focused. Therefore, an effective focus measure operator should be a high-pass filter (HPF). In literature, 2D gradient and other HPF operators are used as focus measure operator. As the sequence of images can be represented as 3D image volume, and the step size in the sequence of input images is very small, we, therefore, present the idea of using 3D gradient filter as focus measure operator for SFF. The better depth map results obtained using 3D focus measure operators as compared to using 2D focus measure operators are shown in the simulation results.