We suggest an active method for overcoming a discontinuous problem of shape from shading. In general the characreteristics of discontinuity doesn''t well come out in scene. Hence we use a camera with the small depth of field so that the attribute of discontinuity is exposed appropriately. In this case 3D information is represented by the degree of defocusing in 2D image plane. And objects in scene can be segmented according to the degree of defocusing. We simulate four algorithms - Brooks Horn''s algorithm the revised its algorithm the resistive net without line processor and the up and low threshold resistive net with respect to the synthetic image. We can see that the success of algorithm depends on the precision of detecting the degree of defocus.