3D衍射光场的点云计算方法与加速

发布时间：2018-02-26 20:17

本文关键词： 衍射场点云全息图采样查找表对称性　出处：《安徽大学》2017年硕士论文　论文类型：学位论文

【摘要】：全息显示能够提供几乎等同于真实世界的三维图像,能充分地传递人类感知三维物体的所有深度刺激,将是三维成像和显示的终极目标。一个视频成像系统包括若干功能性部分,包括获取、压缩、传输和显示等。其中,获取是非常重要的一步。与传统光全息术中采用光干涉方法相比,面向数字全息的计算产生全息图的方法显然具备对环境要求低、灵活性高、可以对物光波的数学描述进行直接编码等优点。但是,三维衍射场的计算涉及信号处理和光学理论等基础性问题,仍然面临诸多挑战,探寻降低三维衍射场计算复杂度的方法以及探讨相应的离散化准则仍是目前的研究热点。计算全息涵盖极其丰富的信号处理问题,例如,Fresnel核既不是带限也不是空间有限的,但它仍然能从它们有限的采样中恢复完整的Fresnel衍射场。根据Wigner分布分析,信号的相干编码比非相干编码情况下包含更多重构所需的主要信息。因此,一方面为了产生生动真实的三维图像,应该计算标量衍射形式二项级数展开的Fresnel(而不是远场Fraunhofer)全息图,导致产生的高空间带宽积和二项级数的复波衍射场给计算全息造成巨大的挑战,另一方面相干的Fresnel衍射场具有一些性质可以用作加速计算方法的基础。计算三维衍射场的方法有很多,本文以点云方法为基础,对Fresnel衍射场的加速计算方法进行进一步探究。首先,通过探究衍射场的采样问题并结合菲涅耳衍射传播在传播方向的可逆性给出一种间接计算方法;其次,通过对查找表方法的研究并结合Gabor波带片或Gabor透镜的条纹图案具有的空间对称性,对原有查找表方法进行改进进而提高计算效率。论文的主要研究内容与创新情况如下:(1)根据点云算法的采样标准并结合菲涅尔传播的可逆性给出双步计算方法,使用该方法可以独立设定源场景与全息面的采样间距。在实际计算过程中根据需要对全息面与源场景设定不同的采样间距,从而在保证人眼观察效果的前提下,有效增大源场景采样间距,减少点云数量,提高计算效率。(2)在新型查找表方法的基础上进行改进,提出一种计算主要条纹图案的新方法,新型查找表方法计算主要条纹图案的过程中,一般设定为同轴全息计算,且样本点与全息面的中心位置都在z轴,通过与全息图的对称性结合,则每次计算时只需计算一个对称区域的全息图,其它位置可以根据对称性直接获取。此方法可大大减少主要条纹图案计算过程中的重复计算,从而进一步提高效率。
[Abstract]:Holographic displays can provide three-dimensional images that are almost identical to the real world, fully transmitting all the depth stimuli of human perception of three-dimensional objects. It will be the ultimate goal of 3D imaging and display. A video imaging system includes several functional components, including acquisition, compression, transmission and display. Acquisition is a very important step. Compared with the traditional optical interferometry in optical holography, the method of generating holograms based on digital holography obviously has the advantages of low environmental requirements and high flexibility. The mathematical description of object light wave can be directly coded. However, the calculation of three-dimensional diffraction field involves some fundamental problems, such as signal processing and optical theory, which still face many challenges. Exploring methods to reduce the computational complexity of three-dimensional diffraction field and discussing the corresponding discretization criteria are still the hot topics. CGH covers a wealth of signal processing problems, such as the Fresnel kernel is neither a band limit nor a limited space. But it can still recover the complete Fresnel diffraction field from their limited sampling. According to the Wigner distribution analysis, the coherent coding of the signal contains more main information needed for reconstruction than in the case of non-coherent coding. On the one hand, in order to produce vivid and real 3D images, we should calculate the Fresnel holograms (not far field Fraunhofer) holograms in the form of scalar diffraction binomial series. The resulting high spatial bandwidth product and complex wave diffraction field of binomial series pose a great challenge to CGH. On the other hand, the coherent Fresnel diffraction field has some properties which can be used as the basis of the accelerated calculation method. There are many methods to calculate the three-dimensional diffraction field, which is based on the point cloud method. The accelerated calculation method of Fresnel diffraction field is further explored. Firstly, an indirect calculation method is proposed by exploring the sampling problem of diffraction field and combining the reversibility of Fresnel diffraction propagation in the propagation direction. By studying the method of lookup table and combining the spatial symmetry of the stripe pattern of Gabor band plate or Gabor lens, The main contents and innovations of this paper are as follows: 1) according to the sampling standard of point cloud algorithm and the reversibility of Fresnel propagation, a two-step calculation method is presented. By using this method, the sampling distance between source scene and holographic plane can be set independently. In the actual calculation process, different sampling spacing between holographic surface and source scene can be set according to the need, so as to ensure the effect of human eye observation. Effectively increasing the sampling distance of source scenes, reducing the number of point clouds and improving the calculation efficiency. (2) based on the new lookup table method, a new method for calculating the main stripe patterns is proposed. In the process of calculating the main stripe patterns by the new lookup table method, the holographic calculation is generally set as coaxial holography, and the center position of the sample point and the holographic plane are both in the z axis, which combines with the symmetry of the hologram. Then only a hologram of a symmetric region is calculated for each calculation, and the other positions can be obtained directly according to symmetry. This method can greatly reduce the repeated calculation in the calculation of the main stripe patterns, thus further improving the efficiency.
【学位授予单位】：安徽大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O436.1;TN27

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