A Study For Dense Full-field Measurement Of Active Depth From Defocus

The depth from defocus uses the direct relationship among the depth of the scene, camera parameters and the degree of blurring in two images to recover the 3D information of the scene. Because the depth from defocus has many advantages over the other range techniques, it has attracted a great amount interest. Between the passive depth from defocus and active depth from defocus, only the latter can obtains the depth of the scene accurately and rapidly. Due to unreliable principle for local filtering, the spatial resolving power and the precision of the depth is limited in traditional active depth from defocus for texture object.In this dissertation, we chiefly research the theory, method andtechnique on the full-field measurement of active depth from defocus toobtain dense depth information about the scene. This dissertation iscomposed of three important parts: the first part includes chapter 1 tochapter 2, in which the traditional method and technique on depth fromdefocus are discussed. The second part is chapter 3, in which themeasurement method and technique for the object with great texturevariance are researched. The last part is chapter 4 to chapter 6, in whichthe theory is setup and the method and techniques are researched on thefull-field measurement of active depth defocus, also the traditional activedepth from defocus is extended to change the illuminate optical system.The main results obtained can be summarized as follows:1. Methods of the active depth from defocus to measure the depth of theobject with great texture variance are proposed. A matrix dot pattern isprojected onto the object and the convolution / deconvolution inspatial domain is used to calculate the degree of the burr of the subimages. With the method, the accurate corresponding pixel betweenthe sub images of the two blurred images can be obtained and theoverlap of image in defocus measurement can be eliminated. To anobject with great texture variance, it may make the measure moreeasily and accurately than traditional active depth from defocus. The principle of full-field dense active depth from defocus is proposed. When an object is projected with sinusoidal grating, the light intensity of the object at the projected frequency on the measured point is equal to the modulation of the same point. By using the ratio of the modulation distributions of the two defocus images, the depth of the object can be calculated. The method not only eliminated limited between the spatial resolving power and depth precision but also may be calculated with simply and apace. A dense depth measurement can be obtained easily and efficiently with the method. The principle and equation of active projecting depth from defocus is proposed, in which, the projecting system parameters rather than image formation system parameters is changed. The full-field method is combined with the new active depth from defocus. A dense depth measurement can be obtained easily and efficiently with the method and more option is supplied to realize active depth from defocus. The precisions of full-field measurement of active depth from defocus under cross-sinusoidal grating projection and sinusoidal grating projection are investigated with a computer simulation and experiment. The precision dependence on the relationship between the direction of texture and the grating is found and the superior illumination pattern is obtained.The setup of calibration and research table are proposed for active full-field dense depth from defocus. It is necessary to obtained the depth measurement accurately and efficiently with the method. The setup of calibration and research table are proposed for active projecting full-field dense depth from defocus with changing projecting parameter. It is necessary to obtained the depth measurement accurately and efficiently with the method.