In high-density stereo correspondence, matching cost aggregation is one of the key links, and the non-local cost aggregation algorithm based on tree structure has attracted people's attention in recent years. On this basis, the clustering algorithm based on non-local tree is studied, and a new cyclic tree structure is given. Each pixel in the image is rooted in eight adjacent tree structures, which we call the first level. We made up the second floor with eight adjacent first floors. Since the algorithm has a natural location in the image pixel structure, it does not need to perform any operations on it. The performance of Middlebury's data set is evaluated, and the results show the application effect of the algorithm proposed in this paper in the current most advanced clustering algorithm.
The dark spots in the speckle pattern are the phase singularities, which contain rich information regarding the phase of the speckle field and determine the distribution of the speckle field. The generation of optical vortices using speckle is a simple, effective, and easy to implement method. we designed an experimental scheme that can generate a optical vortex to explain the properties of phase singularities in a speckle field. Through numerical simulation, we obtained the distribution of the real part zero line and the imaginary part zero line in the speckle field, and drew the singular skeleton of the speckle field, indicating that there are phase singularities in the speckle field.The experimental results are in agreement with those obtained from numerical simulations, thus verifying that the generation of optical vortices can be produced using the scattering method. The experimental scheme is simple and easy to operate.
Diffraction efficiency is a key assessment criterion for the hybrid diffractive-refractive optical systems with a wide field of view. However, diffractive optical elements cannot obtain high diffraction efficiency simultaneously in the case of broad wavelength band and large incident angle range. This character limits the applications of DOEs in the optical systems with large field of view and wide working wavelength range. In this paper, we present a manufacturing method that glued two diffractive optical elements together to reduce the stray light scattered into unwanted diffraction orders. Firstly, the separated DOEs are fabricated with the ultra-precision turning method. Then, through chosen suitable optical adhesives to glue those separated DOEs. Based on the principle of maximum diffraction efficiency on the design waveband and incident angles, we optimized the parameters of the diffractive optical elements to achieve broadband high diffraction efficiency and modulation transfer function over a wide incident angle range. The DOEs enable the system to realize a diffraction efficiency over 90% when the incident angle is no more than 54°. This method is easy to realize and maintain high structural stability. We can give a more precious design than presented methods, such as substrate optical material section and optical adhesives section. The benefit of this design and manufacturing method is that the maximum integral diffraction efficiency overall the wide angles of incidence in the whole waveband can be achieved, thereby ensuring the high modulation transfer function of a hybrid imaging optical systems with diffractive elements.
Phase extraction and applications of the speckle vortex field with spiral wavefront and stable core structures of phase singularities has become an important research content in the field of optical measurement. Phase singularities in the speckle field constitute singular skeleton. We use an experimental system to measure the deformation displacement based on the singular skeleton. In the experiment, a liquid crystal spatial light modulator (LC–SLM) is used to generate speckle field, and the output speckle image is captured by the CCD camera. By processing the speckle pattern, the singular skeleton of the speckle field is depicted. Based on the singular skeleton, the deformation translational displacement of the test sample is obtained. The experimental results show that high-resolution optical measurement methods can be developed based on the singular skeleton of the speckle field.
Linear gratings and circular gratings are most commonly used in the applications of Talbot effect, due to their simple patterns and ease of analysis of Moiré fringes. In the present paper, we demonstrate a scheme to measure the displacement of a deformed object which based on the Talbot effect. We designed a hologram of a two-dimensional square-hole grating. For the test, we used a computer-controlled liquid crystal spatial light modulator (LC–SLM) and the computer-generated Talbot array hologram. The Talbot array hologram is displayed on the LC–SLM screen. The beam diffracted by the grating is transmitted to the surface of an object. By adjusting the distance between the LC-SLM and the object, a clear image is formed on the surface of the object. A speckled pattern of the object surface is captured by a CCD camera. Two speckle patterns before and after the deformation is recorded. The information about the displacement is codified in the intensity pattern. The displacement can be obtained by digital image correlation (DIC). The DIC obtains the displacement components by comparing the gray intensity changes between the digital images of an object surface before and after the deformation. This method is simple and easy, and can be used as an alternative method to measure in-plane and out-of-plane displacements. Theoretical and experimental results are presented.
We investigate effect of atomic densities (N) on propagation and spectral property of large area femtosecond Gaussian pulse (the pulse area is larger than 2π) in a three-level Λ-type atomic medium by using the numerical solution of the full Maxwell-Bloch equations without the slowly varying envelope and the rotating-wave approximations, and the solution is obtained by PC-FDTD method. It is shown that, variation of value of the atomic density has considerable effect on propagation and spectral property and the effect is closely relative to size of the pulse area. For the pulse with area 4π, propagate in the dilute medium with smaller atomic density, clear pulse splitting doesn’t occur, slight pulse spectrum broadening appears, the strength of the spectral component with higher frequency increases with the distance increasing; when the pulse propagates in the dilute medium with larger atomic density and in the dense medium, the main pulse splits into two sub-pulses, and the spectrum broadening in the dilute medium with larger atomic density is much larger than that in the dense medium. For the pulse with larger area 8π, the case of the pulse propagates in the dilute medium with smaller atomic density is similar to that of the 4π pulse; but when the pulse propagates in the dilute medium with larger atomic density and in the dense medium, the case is considerably different from that for 4π pulse, the main pulse splits into three sub-pulses, and the spectrum broadening in the dilute medium with larger atomic density is much smaller than that in the dense medium.
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